# Submarine class XXI

XXI class

Construction drawing
Overview
Type Two-hull ocean-going submarine
units officially in service in total: 118

User: Kriegsmarine

Client, not all built boats put into service
U 2502
U 2506
U 2511
U 2513 passed on to USA
U 2518 passed on to France
U 2529 (N 28), passed on to USSR
U 3008 passed on to USA
U 3017 (N 41)
U 3035 (N 29), passed on to USSR
U 3041 (N 30), passed on to USSR
U 3514
U 3515 (N 27), passed on to USSR
U 2518 (Roland Morillot)
U 2529 (B 28) from UK
U 3035 (B 29) from UK
U 3041 (B 30) from UK
U 3515 (B 27) from UK
U 3535 to U 3542 as TS 5 to TS 12 (1947 as R-1 to R-8)
U 2540 as Wilhelm Bauer
Shipyard

Blohm & Voss , Hamburg
AG Weser , Bremen
Schichau-Werke , Danzig

Order November 6, 1943
period of service

1944-1982

Whereabouts Except for Wilhelm Bauer, all boats were sunk or scrapped
Technical specifications
The data relate to standard values ​​and can vary for each unit
displacement

1,621  tn.l. empty
1,819 tn.l. submerged,
total displacement 2,114 m³

length

76.7 m

width

6.6 m

height

7.7 m + 3.6 m (tower height)

Draft

Construction: 5.77 m
maximum: 6.86 m

Diving depth 133 meters (working depth)

220 meters (battle diving depth)
330 meters (destruction depth)

crew

57 or 58

drive
• 2 × MAN M6V40 / 46KBB, highly charged 6-cylinder diesel with a total of 4,000  PS (2,900  kW )
• 2 × double electric motors SSW GU365 / 30 with 5,000 PS (3,700 kW)
• 2 × SSW GV232 / 28 electric motors for crawl speed , 226 PS (166 kW)
speed

Popped up:

15.37  kn (28.5 km / h) (diesel)
17.94 kn (33.2 km / h) (electric motor)
18.08 kn (33.5 km / h) (electric motor + diesel)

Submerged:

16.5 kn (30.6 km / h) (electric motor)
6.1 kn (11.3 km / h) (crawl speed electric motor)
10.42 kn (19.3 km / h) (when snorkeling)

(max. speeds achieved on U 3503, U 3506 or U 3507)

Range

Popped up:

15,500  nm (28,700 km) at 10 kn (19 km / h) calculated after towing tests, after measurements on U 3507 : 14,100 nm at 10 kn, 15,700 nm at 9 kn.

Submerged:

340 nm (630 km) at 5 kn (9.3 km / h) or 487 nm at 3 kn with creep motors. 120 nm at 8 kn with electric motors.

15,100 nm at 10 kn while snorkeling.

Armament

6
bow torpedo tubes with 20 to a maximum of 23 torpedoes or 14 torpedoes and 12 TMC or 18 TMB mines
2 × 3 cm twin flak M44 (960 rounds / min)
or 2 × 2 cm twin flak C / 38 (450 rounds / min)

The U-Boot-Klasse XXI , officially called Type XXI , was a German U-Boot-Klasse that was built from 1944 to 1945.

These boats were the most modern of their time and were known as electric submarines or electric boats because of their large accumulator system , which allowed them to operate underwater for much longer than other contemporary types . Due to their large battery capacity, powerful electric motors and a shape that is more favorable for underwater travel, they reached a higher speed with their electric motors underwater than with their diesel motors on the surface. They were equipped with a snorkel and designed to be underwater almost constantly. This made them the first “real” submarines, unlike all previous submarines, which were basically only submersible torpedo boats .

The type XXI was assembled in section construction from nine sections; the sections were built on the "assembly line". He was no longer used in combat against enemy surface ships in World War II . Because of its revolutionary properties, the Type  XXI introduced a paradigm shift in the submarine weapons of all countries, although only very few electric boats were still in use, e.g. B. U 2511 under Adalbert Schnee .

The American author Howard Grier described the Type XXI as Dönitz's miracle weapon and, in view of the hope that was placed in these new boats and thus the "final victory", laconically stated that the steel for these 170 new boats would have needed 5100 at that time more urgently Can build tanks.

## history

The international legal doctrines of the cruiser war required submarines to de facto surface warfare against merchant ships in the First World War . All merchant ships showed up to stop and search. After a check, enemy ships could be sunk or taken as a prize , neutral ships without banned goods were allowed to continue voyage. The underwater properties therefore receded, so that a submersible was established that could overtake most merchant ships with diesel engines over water and only dive away to safety when stronger and faster surface warships appeared.

Therefore, the typical submarine had a more powerful propulsion system for over- than for underwater travel, an open bridge for observing the sea area and, in addition to torpedoes , was armed with cannons . These specifications determined the constructions of the submarine types of all countries up to the time of the Second World War . After the introduction of the convoy system and sonar direction finding ( ASDIC ), only a few military personnel were convinced of the success of using submarines ( Nimitz , Dönitz). Indeed, World War II was a testament to the effectiveness of the submarine weapon and brought about fundamental changes in military doctrines .

### prehistory

In the first years of the war the few conventional submersibles of the Kriegsmarine achieved great success. That is why the Main Office of Warship Construction (K-Office) of the Navy High Command (OKM) did not want to provide shipyard capacities for new developments such as the project by the engineer Hellmuth Walter for a powerful submarine propulsion system that is independent of the outside air. The successful test run of the test boat V 80 , which with its new Walter drive in the loop - mouth of an underwater speed of 27 knots reached, little change in this attitude.

The head of the K-Office, Admiral Werner Fuchs , only gave  the Germania shipyard a construction order for the V-300 project - a larger test submarine with Walter propulsion . Walter wanted to build at Blohm & Voss because of the higher capacities , but was passed over. After almost two years of construction work , during which Walter repeatedly had to make concessions, he and Waas from the K-Office arranged for a demonstration of the V 80 in the bay off Hela on November 14, 1941 . The observers should be Grand Admiral Raeder , the commander of the submarines Karl Dönitz and Fuchs. However, Dönitz was not invited by the OKM. Raeder showed great interest; However, Fuchs saw no need for a new type of boat, which, in his experience, would require years of planning and development work and would therefore not be decisive for the war. As a result, on February 18, 1942, a construction contract was placed with the Germania shipyard ( U 791 ), but it was never carried out.

In January 1942, Walter contacted Dönitz directly, who had been interested in Walter developments from the start and recognized their potential. Dönitz emphasized the necessity of high underwater speed in front of the surface properties despite the great success of his submarines at the time and expressed his regret that he had not been invited to the demonstration in Hela. Due to intensive discussions between Walter, Waas and Dönitz, the Walter project was given more weight to the Naval War Command (SKL). After an order to the Lübeck Flender-Werke that could not be fulfilled , Blohm & Voss and the Germania shipyard produced only two small Walter boats with 220 tons (Wa201, later type XVII B) and two small ones from mid-1942 instead of the required pilot series of six Walter boats (WK 202, later Type XVII G) commissioned and built. Illies took up development at Blohm & Voss. For the design , suggestions from aviation and wind tunnels were taken up, so that a usable basic design came about about three months later.

Dönitz also insisted on the redesign of a fast Atlantic-capable submarine (later Type  XVIII ), which was to be built in Kiel after an application from Deutsche Werke AG . It should have about 800 tons of displacement, about 15 knots above water and about 26 knots underwater. The boat shape should correspond to the hydrodynamically well-formed, small Walter type Wa 201. The fish profile with an oval cross-section for accommodating the Mipolam bags with hydrogen peroxide (H 2 O 2 ) under the pressure hull , stabilizing fins for the higher underwater speed and the streamlined closed bridge represented a radical departure from previous designs.

The far-reaching constructive tasks of the new developments presented the Walter company with serious personnel problems. A delegation of experienced front-line officers, suggested by Waas, to act as permanent advisors to the designers and to supervise the trial operation was repeatedly rejected by the OKM. In June 1942 there were again talks between Walter, Waas, Dönitz, Admiral Kleikamp (K-Office) and Gutjahr (Head of Torpedo Office). Dönitz immediately put the chief engineers Heep and Gabler off for the duration of the war. Both then played a major role in the development and improvement of all new submarine types.

Despite the discussions that drove the Walter project forward, the OKM and especially the K-Office were not ready to get the broad-based development ready for series production. Thereupon Dönitz turned directly to Hitler's naval adjutant Karl-Jesko von Puttkamer in autumn 1942 . On September 28, 1942, Hitler ordered a lecture in the Reich Chancellery in which Keitel , Raeder, Dönitz, Fuchs and Waas took part. As a result of the statements by Dönitz and Waas, the OKM's view of the development of submarines has actually changed.

### planning

The new Walter drive did not reach series production quickly enough, and the hydrogen peroxide required as an oxygen carrier was not available in sufficient quantities (the requirements of the entire submarine fleet would have been around 300 tons per day). That is why naval construction director Oelfken (adviser von Bröking) presented the head of the K-Office in April or May 1943 in the presence of the “conventional” submarine designers Schürer and Bröking with a rough draft of Type  XXI with conventional diesel-electric propulsion based on Type XVIII in front. He added: “If we want to build such a large boat and have so much space available, we can achieve a lot more with conventional machinery than before. If, in addition, much more emphasis is placed on the underwater properties, we can of course design a conventional drive differently than in the past. "

An underwater speed of over 18 knots was required because it was assumed that enemy security vehicles could still perform sound location up to this speed. It was assumed for the normal Allied convoys that they would not be able to increase their speed above 10 knots in the foreseeable future. The outer boat shape of the Type  XXI was essentially taken over from the already towed hull shape of the planned large ocean-going submarine Type  XVIII with Walter drive. To accommodate the considerably enlarged accumulator system, an 8-shaped cross-section of the pressure hull was provided in the middle third of the boat. This design promised an underwater speed of 18 knots for 1.5 hours or 12 to 14 knots for 10 hours with 4000  HP = 2942  kW . A speed of 5 knots for 60 hours was expected at creeping speed. In the course of the planning, the boat finally grew to a size of 1,600 tons.

Despite his concerns about this size, Dönitz accepted the design as a replacement for the Type  IX on June 13, 1943. In his opinion, due to the lack of clarification by the Luftwaffe, closer search posts were possible with smaller boats. The critical situation in the submarine war , which the previous types were hardly able to cope with, and the uncertain readiness for series production and the fuel supply for the planned new submarine class XVIII with Walter propulsion ultimately tipped the scales in favor of the immediate solution type  XXI . It was assumed that the lead layer would allow the construction of 250 Type XXI electric submarines by the summer of 1945 and that the Walter drive would then have to be used.

The originally planned Walter boats had a circular pressure hull cross-section that was ideal in terms of printing technology. The 0-shaped cross-section of its outer shell was due to the fact that the fuel for the Walter drive could be stored between the pressure hull and the outer shell exposed to the water pressure. The enlarged type XXI battery system  , on the other hand, could only be arranged within a pressure hull. A somewhat larger, but still circular pressure hull cross-section would have been more favorable. That would have required additional development time for new towing tests and the redesign of the outer shell and thus resulted in a loss of time of around six months. The combination of the 0-shaped outer hull shape of Type XVIII with an 8-shaped pressure hull built into it has a number of disadvantages compared with the circular cross-sections of both hulls:

It was known that a circular shape would have been considerably cheaper for the pressure hull cross-section. Calculations showed that the surface displacement with a circular cross-section would have been 1200–1400 m³ and the mean draft 5.5 m. The 8-shaped pressure hull, however, allowed the use of a battery type that was common at the time. In Germany, an increase in the pressure hull diameter was not desired during the war. It would have required greater sheet metal thicknesses and thus lead to manufacturing difficulties. As a result, the concept of the 8-shaped pressure hull was retained in some subsequent drafts. Post-war buildings derived from Type  XXI again had circular pressure hull cross-sections.

The diverging drive shafts have the advantage that the rudder position hardly needs to be changed in the event of a main engine failure in order to be able to maintain the course . In addition, despite the narrow ship's width, large propellers with good efficiency and low propeller noise could be used. A disadvantage is that the price at the failure of steering gear by different propeller speeds port / starboard can be changed little. In order to obtain the most possible detachment-free tail shape, there was only a single enlarged rudder that was outside the propeller streams . This generates correspondingly low rudder forces at low speeds. The old types, on the other hand, had a rudder behind each of the two propellers in the interests of greater maneuverability . These can generate strong rudder forces even at low speeds as soon as the propellers are running at a higher speed .

The copper shortage in Germany had some consequences for the construction. Many indispensable auxiliary drives (rudder, hydroplane , periscopes , flak towers, torpedo doors of the torpedo tubes ) worked with pressurized oil and a central electric drive instead distributed to the individual systems decentralized electric motors . Since part of the pressure oil system ran on the outside of the pressure hull (depth rudder, flak towers), seawater could penetrate this system in the event of damage . The pressure oil system was then changed. The old boats and post-war buildings usually have electrical auxiliary drives due to their better efficiency, higher reliability and the independent drive power.

Since the detailed designers could not coordinate with each other for reasons of confidentiality, the internal arrangement of some systems was not easy to maintain and repair . On the other hand, the strict secrecy protected the entire project well against targeted air attacks on critical production facilities.

The construction time has been reduced from seven to three months. As early as December 8, 1943, the central design office " Ingenieurbüro Glückauf " (IBG) in Blankenburg (Harz) reported the completion of the design and manufacturing drawings . In order to save time, a prototype was not built, which would not have been expected to be completed until October 1944. Admiral Werner Fuchs' suggestion to have the finished construction checked by the K office was also rejected because of the time required for this, which took three to four weeks. Instead, series production began immediately . Occurring problems should be resolved after the delivery of the first submarines, which were intended for testing and training. Two months instead of the previous five months were planned for the steel construction, and four instead of ten months for the section construction. The planned total construction time was nine months instead of the previous at least 22 months.

For this purpose, the working hours have been increased to 72 hours per week and more. The improper execution of work orders and the non-fulfillment of quotas by factory managers, field officials and skilled workers of all kinds became punishable by swearing in them under martial law. Even in the case of negligence, harsh measures threatened by involving the Gestapo .

### construction

After the completion of the plans, the order for the first 170 boats was placed on November 6, 1943, for which other projects of the Kriegsmarine had to be restricted or abandoned. In the meantime, all the important shipyards in Bremen ( DeSchiMAG / AG Weser , Bremer Vulkan ), Hamburg (Blohm & Voss), Kiel ( Germania shipyard ) and Danzig ( Schichau-Werke ) had become targets of the Allied air offensive and could not guarantee either construction capacities or production reliability.

After the naval armaments were handed over to Armaments Minister Albert Speer , the Main Committee on Shipbuilding (HAS), which had existed since 1942, was redesigned. Speer appointed the general director of the Magirus works , Otto Merker as head. Merker suggested the construction of sections , based on the model of the assembly line production used in motor vehicle construction , according to which the boat should be prefabricated inland in eight individual raw sections, then provided with machines and fixtures in a cyclical process in equipment yards and finally welded together at assembly yards. Construction took about a month with a monthly output of 30 boats. Compared to the old submarine types, the number of construction hours decreased from 280 hours / t for the Type  VII C / 42 in autumn 1943 to 205 hours / t for the Type  XXI in December 1944 with a planned 164 hours / t.

After a transition period, only the Type XXI and the smaller Type XXIII derived from it  were manufactured from 1944  onwards. The production of submarine tonnage rose to around 175,000 t in 1944, despite increased Allied air strikes. However, the first “Führer birthday boatU 3501 launched on April 19, 1944 at the Schichau shipyard in Gdansk was provisionally floatable only with wooden wedges due to the appointment. It had to be dragged into a dock immediately. Instead of functioning fittings, the sections supplied often contained dummies . Nevertheless, congratulatory telegrams arrived from Adolf Hitler, among others, and medals were awarded to those responsible for the launch. The directors of the other shipyards had refused to launch unfinished boats. The result of the hasty launch was rework that delayed the commissioning of U 3501 (without flak towers, later use as a school boat and, after a bomb hit, electricity supplier) until July 29, 1944.

The alignment of the sections at the assembly yards was carried out using two main axes:

• the main axis of shipbuilding and weapons technology, passing through section five (control center and tower),
• the main drive axis, which were defined by section two (electric motor compartment).

For precise alignment of the sections, small holes were drilled in the bulkheads, through which a light in the control center had to be visible from the bow and stern. After precise alignment, the pressure hulls of the sections were welded diametrically by four workers with seven seams in one operation without interruption in eight hours.

One of the basis of the construction of the section was an exact fit of the hull. Very optimistic information from the shipbuilders about the accuracy that can be achieved during construction was not confirmed. The head of the Office for Warship Building, Vice Admiral Friedrich Ruge , noted in his diary with the date August 9, 1944: “The question of responsibility for section building has still not been clarified, deadline pressure too strong. Sections never finished, fittings sometimes only 45%. This largely overcomes the advantages of section construction ”. The first sections of the suppliers had to be improved by the assembly yards, so that the first six boats in each yard were initially intended as school boats due to the lack of a type boat. Further delays occurred due to bad planning, as the construction was created in the greatest secrecy and therefore lacking practical coordination. The constant bombing raids by the Allies also brought delays with them, as production facilities and transport routes were temporarily out of order and had to be replaced or repaired.

The high time pressure, strict secrecy, bottlenecks in the available raw materials and the too late allocation of front-experienced engineers to the central design office "Ingenieur-Büro Glückauf" (IBG) in Blankenburg (Harz) had led to numerous defects in the submarines delivered which came to light in the subsequent tests and required extensive changes and rework. Many designs had to be changed as inexpedient or unusable. The steering gear turned out to be a complete mistake, the first completed boats could not be steered. The IBG's catalog of changes up to September 1944 totaled 150 construction changes. In addition, due to delivery problems, not all of the planned equipment and devices could be installed in every submarine. One part could only be used as a school or test boat. When General Director Franz Stapelfeldt from Deutsche Schiff- und Maschinenbau Aktiengesellschaft repeatedly pointed out the unrealistic deadline requirements, he was relieved of his post at a meeting with General Director Merker at the end of 1944.

The number of boats delivered monthly peaked at 28 in December 1944. By the end of 1944, a total of 61 Type XXI boats  had been delivered, all with defects and not ready for action. In January 1945, the Navy had a total of 418 submarines of various types, the largest number at all, of which 65% were used for training, mostly due to technical defects or combat damage.

In 1945 the production of the sections ceased because important suppliers were occupied and the transport system was largely interrupted or destroyed. The naval armament was switched to an emergency program from January 1945. In March 1945 - two months before the end of the war - almost 40 submarines were launched, the highest number in the entire war. However, the increasing air raids in March and early April 1945 practically led to the cessation of new production. The last boat to be launched was U 3051 on April 20, 1945 at AG Weser , 7 days before the British occupation. At the end of the war, the British troops found 28 more or less finished boats on the slipways , plus a large number of individual sections.

In the end, 118 Type XXI boats were delivered to  the shipyards

• Blohm & Voss, Hamburg, (construction lots U 2501 - U 2762),
• DeSchiMAG / AG Weser, Bremen, (construction lots U 3001 - U 3295),
• Schichau shipyard, Danzig, (construction lots U 3501 - U 3695)

put into service, including 62 boats by the end of 1944.

Only a few boats were ready for the front before the end of the war due to the long training period, which had been estimated for around twelve weeks, and many technical problems. Admiral Werner Fuchs initially rejected their acceptance as being unusable from the front. They first had to be made suitable for this through lengthy modifications. According to his later assessment, the first type XXI submarine was  ready for use at the front from May 1945.

## Technical innovations

The Type  XXI was designed for quick and enduring submarine ride and standard equipped with a snorkel, minimize the residence time on the surface and face down in front of the radar equipped surveillance aircraft and anti-submarine ships to operate. The boat could change its location quickly with the main electric motors or slowly and quietly with the crawler motors, thereby avoiding most of the submarine hunting groups or sitting in front of convoy groups undetected. It was designed for frequent stays underwater and had appropriate supply systems as well as a floating system and automatic depth control.

Camouflage and repellants such as bolts , location-repellent rubber covers on the snorkel head, planned decoy targets , destroyer missiles and listening torpedoes should make it much more difficult to discover and track the boat. New FuMB and FuMO systems (radio measurement observation and radio measurement location systems) promised an early detection of the enemy radar or enemy ships and aircraft, so that an attack could be avoided early and quickly. New sonar technology (S system) made it possible to actively locate the enemy and should later allow torpedoes to be fired from a depth of 50 to 60 meters depending on the location. With the torpedo fast-loading system, all torpedoes on a convoy could be fired with a high probability of being hit.

### Underwater operation

The air volume of the boat was about 900 m³. Without air renewal, with a crew of 60 and less, mainly sedentary work, the CO 2 content of the breathed air increases within 11.3 hours from an initial 0.03% to 1.5%. The oxygen content of the air drops from an initial 21% to 17% after 27 hours.

A CO 2 concentration of 4% can only be tolerated for a short time, 5% is poisonous. To limit them, there were two air renewal systems. They were used from 1.5% CO 2 content and essentially contained loose soda lime to bind the CO 2 . The soda lime supply was sufficient for 112 fillings, one filling under normal conditions for four to five hours (a total of 19 to 23 days).

The oxygen content should not fall below about 17% and was supplemented from this limit from 30 oxygen bottles , each with a volume of 50 liters and 150  atmospheric pressure. For U 2513 and U 3008 , 24 bottles are specified , for U 2540 23 bottles. From 25 cartridges “IG briquettes” , in which oxygen was firmly bound chemically, further oxygen could be released with the wet drawing device in the control center. Each cartridge delivered 1.5 m³ of oxygen within 50 minutes. The entire oxygen supply in the boat was sufficient for a dive time of 150 hours (about 6 days).

With an air drying system from the manufacturer BBC , separated water could be fed into the wash water cells via a heat exchanger and a cooling system. For the first time on German submarines, a wet room was installed in section 6 (front living room), which contained three wash basins, a hot water shower and two toilets. The waste water was disposed of in holding tanks so that the system could also be used when it was submerged. Another toilet was located in section 1.

The galley , located amidships in section 5, was equipped with a three-burner electric stove, built-in kettle, two sinks with a hot water generator, refrigerator and storage cupboards. Under the galley, storage and cooling rooms, including a deep-freeze room, were installed, which could be reached via a companionway .

Whereas in previous boat types only one berth for two men was provided, most of the 57 (regular) crew members now had their own of the total of 47 berths, with UV lamps to replace sunlight. 24 crew berths were located above battery room I in section 4. The chambers of the commander, the chief engineer, four officers 'berths, five sergeants and twelve non-commissioned officers' berths were located in section 6 above battery room II.

### Positioning and messaging systems

Tower of a Type XXI boat with a Hohentwiel antenna, periscopes and a snorkel mast

The equipment of the radio room essentially corresponded to the equipment of the Type IX-C from 1944, but without a long-wave transmitter:

The power supply was provided by the radio switchboard with alternating and direct current as well as a transmitter of 1.5 kW in the auxiliary machine room.

On the used rod antenna lower performance was considered by the long net guard - antennas of previous submarines expected. It could be extended to a periscope depth of up to 6.2 meters above the water surface. There were also two manually extendable VHF rod antennas for overwater travel. There were also two long wire antennas from the tower cladding to the bow and the aft area of ​​the boat.

Fu-MB-26 antenna on U 889 ( type IXC / 40)

Initially, the aircraft of the British Coastal Command were equipped with the "ASV Mark II" on-board radar, which operated on a frequency of 200 ± 15  MHz = 1.5 meters wavelength . In February 1942, the American centimeter wave radar "AS-G" was requested for mass production of aircraft. It was able to locate convoys at a distance of almost 160 km and surfaced submarines over 17 km away. The "SG" variant for ships followed a short time later. The British "ASV Mark II" on-board radar was introduced in spring 1943 and worked with a frequency of 3  GHz = 10 cm wavelength.

This made the first German radio monitoring device "Fu MB 1" Metox and the improved "Fu MB 9" ineffective , working in a frequency range of 113–484 MHz = 2.65–0.62 meter wavelength . The German leadership only received reliable information about this in 1943, after a British Short Stirling bomber had been shot down near Rotterdam ( Rotterdam device ), and the losses of conventional German submarines reached dramatic proportions in May 1943.

For radio measurement monitoring and warning of enemy radar radiation served in the new type  XXI of the pulse amplifier "Fu MZ 6 Naxos  " 1 Fu MZ "Ia" or "Fu MZ 7 Nela II" with sight radio for optical observation. The detector receiver "Fu MB 10 Borkum" from NVK / Telefunken (NVK: intelligence test command in Pelzerhaken ) used for this purpose had a very large frequency range that was practically only limited by the antenna .

When traveling above water, it was possible to receive radar radiation in the 9 cm range = 3.3 GHz with the simple λ / 4 rod radiator "Finger" and "Cuba Ia Fliege". The frequency of the latest Allied radar device developed without the knowledge of the Germans, which worked with a wavelength of 3 cm = 10 GHz, was no longer recorded by the Naxos radar detector.

From October 1944, the large-diameter DF system "Fu MB 26 Tunis" from NVK / Telefunken with the receivers "Cuba Ia Fliege" (15–8 cm = 2.0–3.7 GHz) and “Mücke”, which can only be used for overwater travel, was planned (4.5-2 cm = 6.7-15 GHz). All the antennas mentioned so far were non-pressure-resistant makeshift solutions, as the cables had to be led through the open tower hatch.

Antenna "BALI" for radar detector Naxos on board U 505 (Type IX C)

The pressure-resistant decimeter wave antenna "Bali 1" on the snorkel head had a frequency range of only 100–400 MHz = 300–75 cm wavelength. An observation option for higher-frequency centimeter radar radiation when snorkeling was only planned for follow-up projects.

The type XXI 1945 was to receive corresponding systems  . The Bali system should be expanded to a frequency range of 100 MHz to 1.5 GHz = 300–20 cm wavelength. The “Fu MB 35 Athos” sector direction finder from NVK / Funkstrahl for 1.5–15 GHz = 20–2 cm wavelength was being tested on the U 249 ( Type VII C ). It consisted of the “Athos” receiving head, the “Westerland V Fu MZ 13” isolating amplifier, the “Westerland Fu MZ 12” pulse amplifier and the “Norderney Fu MZ 8” alarm device. The receiving head was on its own extension mast and had pressure-resistant centimeter antennas with a bearing facility for 9 cm = 3.3 GHz and 3 cm = 10 GHz. The telescopic mast should be installed in place of the intended but not implemented panoramic viewing tube. - on the receiving head was for locating (aircraft) headlights an infrared -Rundwarnsichtgerät "Flammingo II" of NPC / Zeiss provided.

The radio measuring device Hohentwiel (radar) U or U1 (Fu Mo 61 or 65) from C. Lorenz AG enabled the active location of air and sea targets during surface travel. It could not be used when underwater. The pulse transmission power was 40  kW , the frequency 556  MHz = 54  cm wavelength . The distance measurement accuracy was 10% of the measured value, the bearing accuracy ± 1.5 to 2 ° . Because of the low installation height, the average detection ranges were relatively small: destroyer 4 to 5  km , 1500 GRT - merchant ship 6 km, 6000 GRT merchant ship 10 km, aerial targets 9 to 40 km. The device was also shaded by the later support of the night air target scope in the range from 18 ° to 50 °.

#### Listening system "balcony"

Compensator of the group listening device in the Wilhelm Bauer museum boat: filter amplifier at the top, display scale in the middle, volume control, filter selector switch, handwheel, delay chains at the bottom

The passive acoustic group listening device ("balcony") installed under the bow worked with 2 × 24 membrane - crystal - hydrophones arranged in a horseshoe shape . The sensitivity of a crystal was about 0.1  mV / µBar . The selection of the boresight done purely electronically via a signal propagation time - compensator of Atlas works . The listening system had an average accuracy of ± 1 ° with a maximum deviation of ± 1.5 °. Under favorable conditions, the group listening device already available on earlier boats could detect single ships up to 20 km away and convoys up to 100 km away. The passive German listening systems were thus superior to the American and British. The ranges that could be achieved in practice were lower and heavily dependent on the so-called "sound weather" in the water. They could fluctuate between 30 and 300% of the guide value within a day.

When planning Type  XXI , it was completely overlooked that its higher underwater speed would also place higher demands on the acoustic design of the listening system and the hull. It was not until February 1944 that the BdU made demands for listening possibilities even at the planned maximum speed of 18 knots.

Tests with the U 2511 resulted in a listening speed limit of 9 kn. A version of the listening system that did not detach at higher speeds was installed from the fifth XXI boat. U 2506 reached a listening range of 8000 m at 11 kn, 80 m water depth and sea state 4 off Pillau against the target ship Danube, which was running at 10  kn . During these tests, crackling glitches were observed. Under unfavorable listening conditions at 11 kn, 80 m water depth and sea state 2 off Hela, U 3504 achieved a listening range of 4000 m against the target ship Danube, which was running at 10 kn . At the end of February 1945, tests were carried out on U 3003 with a better disguised listening system, which allowed a listening range of 3000 to 4000 m at least in advance without spikes at 15.5 kn. Due to the end of the war, it was no longer installed in other Type XXI boats.

#### SU system "Nibelung"

The active acoustic horizontal plumb line "Nibelung", which could determine the direction, distance and approximate speed of the enemy with just a few impulses, enabled "program shooting" without periscope control. The sound waves were transmitted with 4.4 kW at around 15  kHz with a pulse length of 20 ms via magnetostrictive oscillators and the echo was processed by a special analog computer (torpedo computer ). The single pulses was attentive enemies with the ASDIC Plant indeed seen, but with the time used amplitudes - bearing not einpeilen.

The calculated settings were continuously transferred electromechanically to the torpedoes, whereby position-independent torpedoes (LuTs) could be fired from a maximum depth of 20 m (work was still being carried out on the shot from 50 m or 100 m). The transmitter and receiver were housed in the foremost part of the tower without hydrodynamic separation. The transducer base could be rotated ± 150 ° to either side from the fore-alignment. The plumb range was approximately ± 110 ° on both sides, ± 140 ° at low speed levels, the maximum bearing error 1.5 °. Depending on the water conditions, the bearing range was 5 to 10 km for slow diving and larger ships. A distance measurement accuracy of ± 2% of the measured value was expected. A bearing was also possible during a snorkel trip.

The recipient worked according to the phase method with sum and difference procedures. The output voltages of the receiver were fed via transformers to the deflection plates of the cathode ray tube DG-9 (Braun's tube), on which an oblique line now appeared, which could be set vertically by turning the base. This “zero” bearing provided the direction and distance of the target with a minimum of three pulses. With a hearing aid, the relative speed of the target could be measured via the Doppler effect . The first systems were installed from winter 1944/1945, but only on a small part of the completed XXI boats until the end of the war . There were only a few technical defects that were fixed from January 1945.

#### Periscopes

The periscopes of all German submarines were manufactured by Carl Zeiss and were one of their particular strengths. The relatively elaborate construction of the standard periscope used in World War II is described as the dream of every submarine commander.

The type  XXI was originally to have an extended attack and night air target sight tube with an optical length of 9 m and a free length of 6.3 m. This was considered necessary to be able to snorkel and attack safely with the increased underwater speeds.

The tests showed, however, that the extended periscopes only remained vibration-free up to 5 kn, from 6–7 kn there was no longer any possibility of aiming. For this reason, the previous standard periscope of the StaSR C / 2 type with an optical length of 7.5 m, which was vibration-free up to 8.5 kn, was installed in most boats. The night air target sight tube of the type NLSR C / 8, which is important for snorkeling, was made vibration-free up to 8 kn by a 1.4 m long guide tube that was firmly connected to the periscope block. The associated shadowing of the own radio measuring device from 18 ° to 50 ° was ultimately accepted, since the surface use of the Type  XXI had meanwhile lost its importance.

The extension speed at full oil pressure was 0.54 m / s for the attack scope and 1.04 m / s for the night air target scope. The panning took 5 seconds without a panoramic view and 34 seconds per revolution with a panoramic view.

#### Defense and camouflage means

British Boldschleuse in the museum
boat Wilhelm Bauer (not original condition)

During a snorkel trip, only the snorkel and the periscope are possible radar targets . The large snorkel head was therefore given a reflection-reducing rubber cover with the cover name "chimney sweep", which reduced its radar cross-section to around 30%.

During the Second World War, active sonar was only effective to a depth of 400  ft = 122 meters. Due to its streamlined smooth surface of the type offered XXI a weaker target for active sonar when the older and much smaller type VII C . Most of the sonar echo came from the tower and other irregularly shaped surfaces.

A Bold sluice for decoys was provided against enemy sonar detection , through which cans filled with calcium hydride were ejected. The so-called Bolde float in the water and generate bubbles of hydrogen that were supposed to simulate other location targets and interfere with the location. Since these decoy targets lacked the Doppler effect of a moving submarine, they could be recognized as such. The Boldschleuse installed in the Wilhelm Bauer museum boat is a British product that was only developed after the end of the war.

In addition, there was “Sieglinde”, a noise body initially manufactured by the Elac company , which was supposed to simulate an older type of submarine with electric motors at four to six knots for up to 30 minutes. This was carried by U 2511 on its patrol.

The “Sigmund” noise disturbance buoy, which is not part of the standard equipment, was intended to clog enemy listening devices with a 10-minute series of bangs 10 seconds apart. The boat should be able to go at maximum speed without its bearing being possible. It should not have been installed until the end of the war.

The following were also planned:

• The noise body "Brunhilde", which, with the same dimensions as "Sieglinde", was supposed to simulate the loud sound radiation of a snorkeling submarine. At the end of the war, the development was not yet completed.
• The decoy “Thetis US”, a gas-filled rubber bag with a reflective body inside, which should generate the same radar echo on the water surface as an undisguised snorkel head.
• "Ursel", a missile system for active defense against enemy destroyers . A solid rocket torpedo with a length of 1.8 meters and a mass of 80 kilograms was planned, which should carry 15 kilograms of explosives. It was expected that at a speed of 60 knots and 300 meters away, a leak about five square meters could be made. Since the "Ursel" project was not ready for series production , the boats were given a workshop with a lathe instead .

### Armament

#### Torpedo facility

The remaining four torpedo tubes of the
Wilhelm Bauer museum boat

Six torpedo tubes , three on top of each other, with a larger diameter than the torpedo caliber of 53.3 centimeters (21 inches ) were arranged in the bow. In contrast to the piston ejection of earlier German submarine types, the type  XXI 's torpedoes were on guide rails in the tubes and were ejected with compressed air. To prevent the air from escaping to the surface of the water after the shot, the pipes were inclined downwards by 2 °. The muzzle flaps were operated hydraulically, if necessary by hand. After the shot, the water penetrating from the outside pushed the air back and through a compensating valve into the torpedo drive cells. With the counterbalance, the muzzle flaps closed automatically. The reserve torpedoes rested on six pairs of bearing arms. The four upper pairs each had three, the two lower pairs each two torpedo bearings. A torpedo store was also located under the floor slabs.

During longer patrols, however, three storage areas had to be kept free so that the torpedoes could be pulled out of the tubes and serviced. As a result, only 20 torpedoes could then be carried. The transverse transport of the torpedoes on a bearing arm was done by sliding cheeks that could be moved by long electrically operated screw spindles. The reloading of torpedoes from the bearing arms was also carried out by e-capstan motors. Reloading six torpedoes from the quick-charge position took 5 (or 15) minutes, the next charge took about another 15 (or 19) minutes. The reloading system also met requirements for low noise development.

A single Type XXI boat could have shot 18 torpedoes at a convoy within a relatively short time, for which a theoretical hit rate of 95% with position-independent torpedoes (LUTs) was determined for ships over 60 m in length. A special adjustment device for the LUTs was housed in the bow space in order to be able to shoot from a maximum depth of 20 m according to the information provided by the SU system (not possible deeper due to the existing torpedo tubes and ejection devices). However, intensive work was carried out on a so-called OT-I shot (shooting depths from up to 50 m). The OT-II shot was planned with a depth of up to 100 m.

The active fight against destroyers was possible with acoustically self-guided torpedoes . Their use was, however, impaired by defensive measures such as towed noise buoys or the speed reduction of the ships. The hit rate was significantly overestimated during the war, especially because numerous terminal and wake detonators were mistaken for torpedo hits. According to a post-war investigation by Jürgen Rohwer, the actual hit rate was 15%.

For electric motor pedos (ETo) there were three converters for recharging the accumulators . About the torpedo tubes, two shot recipients were mounted over which certain of Torpedo computer Derivative readings were electro-mechanically fed into the torpedoes.

It should also be possible to carry 18 TMB or 12 TMC mines in the torpedo tubes , with 14 torpedoes left on the camps. By the end of the war, however, no mine ejection device was ready, so the mines could only have been ejected with compressed air, i.e. with a strong surge of air. In fact, no XXI ever ran out of mines.

#### Flak towers

Flak tower aft, streamlined integrated into the tower

Due to the demands of the BdU for anti-aircraft armament , the Type  XXI had two rotatable anti-aircraft towers protected with 17 mm armored steel on the main tower in front of and behind the bridge. The bridge was also protected with 17 mm armored steel. The pressure-resistant part of the main tower was made of 40 mm armored steel. The value of the flak towers was controversial as they caused a substantial increase in the tonnage and water resistance of the boat. Even Hitler thought they made little sense. Their accessibility later turned out to be poor, their occupation delayed a later alarm dive considerably.

Originally, two 3-cm M 44 anti-aircraft guns from the Brünn arms factory of the Skoda-Werke were planned, which were to hydraulically follow the target device and, according to an American test report, were also available on the U 2513 and U 3008 . The ready-to-use ammunition in two watertight tanks per tower contained 2 × 250 rounds each, the total ammunition supply 3800 rounds. Due to problems with the compressive strength, only a few test samples of the 3 cm flak could be delivered. Therefore, conventional two 2-cm Flak 38  M II with 800 rounds of ready-to-use ammunition each were installed in two ammunition containers and a total of 3450 rounds of ammunition. Their rate of fire was 450 rounds / minute, the firepower was relatively low. The directional range of the flak towers was ± 120 ° (± 170 °), the elevation range −10 ° to + 90 °. The turning speed at full oil pressure was 43 ° / s, the elevation speed 50 ° / s.

In contrast to the 3.7 cm flak that was later installed on conventional German submarines, the 2 cm anti-aircraft gun was considered to be relatively reliable, but not sufficiently effective against lightly armored Allied anti-submarine aircraft. Some of the aircraft had a 5.7 cm on-board cannon ( Ordnance QF-6-pounder-7-cwt , called "Tsetse") in order to be able to attack outside the range of the anti-submarine anti-aircraft guns. Nevertheless, some kills were achieved with the flak towers towards the end of the war.

### Propulsion system

Part of the central control station of the Wilhelm Bauer museum
boat (not original)

The propulsion system consisted of a snorkel for diesel underwater travel to periscope depth , two marine diesel engines , six partial batteries with 62 battery cells each for an external air-independent power supply, two combined main electric motors and generators, two low-speed electric motors, shafts , gears and couplings for power transmission , Auxiliary machinery and two propellers .

#### Snorkel facility

The Dutch lieutenant captain JJ Wichers had already applied for a patent for an extendable air mast after the First World War. In 1939 the Dutch Navy had successfully experimented with snorkeling (snuiver) on the boats O 19 and O 20 .

During the occupation of the Netherlands in 1940, the completed or under construction snuiver boats O 25 , O 26 and O 27 were taken over by the Navy. O 26 was renamed UD 4 and used for snorkeling tests in the Atlantic. Shortly afterwards, the air masts were removed, as was the case with the Dutch submarines that had arrived in England . The German authorities had come to the conclusion that this technology was superfluous ballast that could not be used in the rough Atlantic.

In a letter to Dönitz on May 19, 1943, Walter again suggested a snorkel. The decisive factor for the practical feasibility was his new idea of ​​sucking the air for operating the diesel engines from the inside of the boat for up to 60 seconds when the snorkel was cut under the snorkel.

Depending on the sea state, engine power, boat size and pressure drop until the diesel is switched off, this leads to additional stress on the crew due to air pressure fluctuations of up to 200  mbar inside the boat. If the exhaust gas back pressure is too high due to too deep undercutting (e.g. due to depth control errors), the diesel engines can stop and their exhaust gas can escape backwards from the intake ducts inside the boat. This can lead to gasification of the boat and endangerment of its crew. Type XXI snorkeling is described as a nightmarish experience that had to be kept to the bare minimum. This was accepted because of the danger posed by radar- equipped aircraft and surface units. It was now possible to drive the diesel engines at a depth of about 16 meters (lower edge of the keel), to charge the batteries, to supply the boat with fresh air and yet remain largely undiscovered. U 977 and U 978 , two type VII C boats with snorkel masts that can be laid down on deck, were under water for 66 and 69 days respectively. Initially, it was expected that periscopes and snorkels could be camouflaged against radar location without great effort.

From the autumn of 1944, the Allied radar could also locate a snorkel head or periscope. The then best aircraft radar "APS-20" (Cadillac project, frequency 2.88 GHz = 10.5 cm wave length, impulse ), introduced in March 1945, was able to operate in swell up to strength 2 (weakly moved, wave height 0.1 to 0.5 meters) -Transmission power 1 megawatt) locate a snorkel up to 13 miles (approx. 20 km) away. In swell from strength 3 (foam heads, wave height 0.5 to 1.25 meters) it was no longer usable. In addition, it was not easily possible to distinguish the snorkel heads of the submarines from other objects floating on the water with radar alone.

The “chimney sweep” absorption layer was developed as a countermeasure . With the Jaumann absorber named after physicist Johannes Jaumann , it had a residual reflection of less than 10% in the range of 30 to 3 cm = 1–10  GHz . It was expected that a snorkel camouflaged with this would be able to be located with a centimeter wave radar with a residual reflection between 0.25 and 8% and a detection range reduced by at least 65% at a maximum distance of 5 km.

The maximum diving depth that the absorption layer should withstand without permanent loss of its effectiveness was specified as 150 meters and around 200 meters expected. About 60 submarines of different types were equipped with it. However, the Jaumann absorber was 68 mm thick and unsuitable for mounting on multiple curved surfaces. It required a modified snorkel head valve with a ring float instead of the previous ball float. In tests, the ring float valve showed a slower closing behavior than the ball float valve.

As a result, most of the XXI boats were given a 4–8 mm thick corrugated rubber cover, which was referred to as Wesch absorber or Wesch mat after Ludwig Wesch , the head of the Heidelberg Institute for World Post and World News , founded in 1941 . It was less effective in terms of radar absorption , but it could also be attached to the ball float valves. The radar echo was reduced with the Wesch mats in the range of 20 to 3 cm wavelength = 1.5–10 GHz to an average residual reflection of 10%. The maximum of the residual reflection in this area was approx. 30% (at a wavelength of 5 cm = 6 GHz). The minima of the reflection curve were below 5% at 9 cm = 3.3 GHz (British Rotterdam device ) and below 10% at 3 cm = 10 GHz (American MEDDO device). For the British Rotterdam device, this was expected to reduce its detection range by 50%.

A pressure-resistant decimeter wave antenna "Bali 1" with a frequency range of 100–400  MHz  = 300–75 cm wavelength was located on the snorkel head as a warning of enemy radar location. This limited the area of ​​application of the “Borkum” warning receiver , which had a very large frequency range. In 1945 the Type XXI was also to receive a further developed Bali system with a frequency range of 100 MHz to 1.5 GHz = 300–20 cm wavelength. Pressure-resistant centimeter antennas with a direction finding facility for 1.5–15 GHz = 20–2 cm wavelength and an infrared all-round warning device for locating (aircraft) headlights were also provided on a separate extension mast .

The snorkel could be extended in 2.7 minutes with an air motor and retracted in 1.5 minutes. The compressed air motor was extremely loud when it was used; 95–116 Phon were measured in the control center . A manual drive was available for emergencies. The snorkel head had a float-operated snorkel head valve for the supply air, which should close automatically when it was flooded. The float-operated valves were not free from faults. Their function was dependent on the course of the boat in the direction of the sea, and there was no remedy for icing. In the winter of 1944/45, tests were carried out on some submarine class II boats with compressed air-actuated head valves, which worked properly and quickly.

The cross-sections of the snorkel facility, which was only planned after the completion of the boat construction, were too small for the installed engine power. For supply air they were 43% and for exhaust gas 55% of the values ​​for overwater travel. During the tests, this resulted in considerable problems with the performance and exhaust gas temperature (maximum permissible 600 ° C) of the diesel engines due to excessive intake negative pressure and excessive exhaust back pressure. During normal snorkeling, the negative pressure in the boat was 64 mbar and the exhaust back pressure was 0.35  atmospheres .

The snorkel facility had a relatively large water resistance due to its two circular pipes. Since strong vibrations occurred in the range from 6.5 to 8.5  kn , only speed levels between 0 and 5.5 kn (battery charge) and 9 to 10.5 kn ( cruising ) were permitted for their operation .

#### Diesel engines

Diesel generator in the Wilhelm Bauer museum
boat (not an original engine )

The two MAN M6V 40/46 are based on the 8-cylinder M8V 40/46 engine, which was proposed for the so-called Spanish boat E1 in 1926 by the Ingenieurskantoor voor Scheepsbouw (IvS). The 6-cylinder type 40/46 were already installed on the U 27 (type VII A). The USS Cachalot was equipped with 9-cylinder engines of the revised 40/46 series in 1933. The M6V was a single-acting, non-reversible 6-cylinder four-stroke engine with a cylinder diameter of 400 mm and a piston stroke of 460 mm. The power-to-weight ratio was 14.4 kg / hp.

The gears of the diesel engines reduced their speed in a ratio of 1.65: 1 and were coupled to the engines by a hydraulic Vulcan coupling with a slip of 2%. When the AK was moving, the propellers turned at 315 min −1 . In diesel operation, the electric machines and gearboxes with attached pumps were constantly turned, as it was assumed that the batteries were always charged with diesel operation. Therefore the mechanical efficiency of the diesel at the drive shafts was only 88%.

With the Buchi turbocharger Vta 450 of the BBC Mannheim should by 40% at a high charging supercharger rotational speed of 12,240 min -1 at 522 min a maximum power of 2 × 2000 PS = 2 x 1471 kW -1 are achieved. With charging, a diesel output of 15.4 kn could be achieved over water at 2 × 2000 HP = 2 × 1471 kW. With the full addition of electric motors with 2 × 1347 A = 6 hours of electricity, the U 3507 achieved a speed of 18.08 kn with 2 × 2,380 hp = 2 × 1750 kW and 544 min −1 . Without charging and the addition of an electric motor, a diesel output of 2 × 1400 HP = 2 × 1030 kW at 470 min −1 was achieved over water of 14.6 kn.

The high turbocharging made a very large valve overlap of 150 ° necessary, which resulted in increased sensitivity to back pressure. As a result, when snorkeling, the boost pressure could drop so far that the engine output dropped sharply or, in the worst cases, the engine stopped. A second valve cam set (snorkel setting) was therefore attached to the control shaft , which reduced the valve overlap. This reduced the diesel output to 2 × 1400 HP = 2 × 1030 kW at 470 min −1 , and the charger only ran at 10,000 min −1 . U 3503 achieved a speed of 10.4 kn while snorkeling with both diesel engines, 395 min −1 engine speed and 7500 min −1 supercharger speed.

The decrease in diesel performance when snorkeling was a significant problem, because it took a relatively long time to charge the battery from 10 to 90% charge level at 6.2 hours. The “excessive” battery charging time required to fully charge was assessed by American experts after the war as a major disadvantage of the Type  XXI , which reduced the advantage of the high underwater speed. Since the speed when snorkeling with the batteries charged by both diesels (drive with crawling motors) was a maximum of 6 kn, it should not have been possible to catch up with a convoy when the battery was used up. According to American test reports (U 2513 and U 3008 ), the diesels also had exhaust gas temperatures that were too high when snorkeling. These were well above the safety tolerance of the metal in the exhaust valves of the engines and forced a reduction in output to 2 × 850  HP = 2 × 634 kW (at 12 kn).

The on-board practice showed that the previous snorkeling performance could also be achieved without charging. Since the surface properties were of secondary importance, the installation of the turbocharger was dispensed with in later versions. The maximum diesel output with snorkel was then 2 × 1200 HP = 2 × 883 kW at 10.9 kn. In practice, however, 6 kn could hardly be exceeded because of the periscope and snorkel vibrations.

On December 15, 1944, it was found that there had already been severe engine damage on three Type XXI boats due to water hammer in the cylinders following operating errors. The reason was always the suction of water through the exhaust system by turning the diesel engine when reversing with electric motors.

#### Battery system

The battery system consisted of 2 × (3 × 62) = 372  Bleiakkumulatorzellen type AFA 44 MAL 740W, each with 620  kg mass and a total mass of 236 tonnes . The capacity of each cell was at 30  ° C , 5530  A discharge current and 1 hour 8 minutes discharge time 6267  Ah , at 4560 A and 1.5 hour discharge time 6840 Ah, at 1834 A and five hour discharge time 9170 Ah, at 565 A and 20- hourly discharge time 11,300 Ah and at 243 A and 50-hour discharge time 12,150 Ah. The final discharge voltage was between 1.60 volts per single cell at 5530 A discharge current and 1.80 volts per single cell at 565 A discharge current. The manufacturer was Akkumulatoren-Fabrik AG ( AFA ).

With an average discharge voltage of 2.0 volts per cell, the arithmetical total storage capacity is 8.4 megawatt hours . The energy density is 35.6 Wh / kg for other German submarines and lead accumulators usual range. The main difference is the absolute size of the battery system. The battery cells were distributed over two decks in 2 × 3 = 6 sub-batteries of equal size. The division into three port and three starboard partial batteries allowed the loss-free reduction of the supply voltages of the crawl speed electric motors from 360 to 120 volts. The anchors of the main electric motors, on the other hand, were only supplied with 360 volts from all port and starboard partial batteries. Their excitation windings , which consume up to 2 × 15 = 30 A per motor, were fed from the middle sub-batteries via regulators. The excitation windings of the crawl speed motors were also supplied from these partial batteries. The electrical auxiliary machines worked with 120 volts from different partial batteries.

Significant voltage drops occurred in the cables between the battery and the electric motor. The battery voltage collapsed at high discharge currents of 2 × 5540 A for maximum travel below the intended 2 × 360 volts (= 1.94 volts / cell) to 2 × 336-305 volts (= 1.81-1.64 volts / cell) . The battery system was already discharged after a maximum travel of one hour and 20 minutes instead of the planned maximum travel of one hour and 40 minutes. With a lower current load due to medium and low speed levels, however, the discharge time corresponded to the expectations.

The port and starboard partial batteries could only be recharged in series . Separate recharging of individual partial batteries was not possible. Therefore, the power requirements of the auxiliary machines had to be distributed to the partial batteries during operation. Normal recharging began in the first charging stage with a current of 2040 A each up to a charging voltage of 2 × 446 volts = 2.40 volts per cell. In the second charging stage, the current was reduced to 510 A while the voltage remained the same. In the third charging stage, a constant 510 A current was charged up to a voltage of 2.7 volts per cell.

It was calculated that with a 5 kts submerged cruise with crawler motors every 24 hours, 3 hours of battery charge with snorkel were sufficient to keep the charge level between 60 and 90%. Since the diesel output was only 2 × 1050 HP = 2 × 772 kW when snorkeling with the battery charged, it took a battery that was down to 10% discharged to recharge at about 6 knots (drive with crawling motors) until the second charge level was completed (90% state of charge) 6.2 hours. In tests at the pier (shore power supply was possible), however, charging times of 2.5 hours were achieved for the first two charging stages. For the third charging stage (up to 100%), which was necessary to maintain the capacity at certain time intervals, a further 2.4 hours of charging time was calculated, which results in a full charging time of 8.6 hours for a snorkeling trip.

The battery cells separate out oxyhydrogen , an explosive mixture of hydrogen and oxygen, when they are charged, when they are heavily discharged and in small quantities even when the vehicle is stationary . The overcharge of each Ah decomposes water through electrolysis into 0.42 liters of hydrogen and 0.21 liters of oxygen per cell. With 372 cells and the constant current charge of 510 A used for the third charging stage, up to 119 m³ of oxyhydrogen (79.3 m³ hydrogen and 39.6 m³ oxygen) per hour are released in the ideal mixing ratio for an explosion. In air, hydrogen becomes explosive from a content of four percent by volume.

The battery ventilator used to dilute the hydrogen during overwater and snorkeling trips had a throughput of 4200 m³ / hour. During the snorkeling trip, its exhaust air was sucked off by the diesel engines. The low-noise battery circulation fan used for the individual extraction of the battery cells during diving trips had a throughput of 200 m³ / hour. The hydrogen was catalytically burned by a hydrogen filter upstream of the fan . This allowed the immediate transition from battery charge to diving trip despite the possibility of post-gassing of the battery cells.

Nevertheless, battery explosions occurred in four boats before the end of the war and in U 3017 after the end of the war (under British command). In two cases the cause was an excessively high acid level in the battery cells, which later blocked their ventilation. In the case of the U 2507, it was a spark on the battery exhaust fan and in the case of the U 3002, the hydrogen filter of the battery circulation fan, which did not function in the presence of moisture, and leaks in the drive motor of the fan. The hydrogen filter was therefore rarely used and later not installed.

When questioned, an experienced German officer told the British Navy that the main battery cables ran into the bilges under the battery rooms. The poor insulation of the cables and the presence of bilge water cause electric arcs . With poor ventilation of the battery, which releases large amounts of hydrogen when charging, the probability of an explosion is relatively high.

The average life of the battery cells was 18 to 21 months. Towards the end of the war, attempts were made to increase the capacity with a larger number of thinner lead plates, at the expense of a shorter service life. For the test type 70 MAL 760 with 9600 Ah at 6000 A discharge current, the service life was a maximum of 12 months, for the test type 60 MAL 760 with a slightly lower capacity, 15 months were estimated.

#### Main electric motors

View into the electric engine room of the
Wilhelm Bauer museum boat
Starboard main electric motor of the museum boat Wilhelm Bauer

The two completely new electric machines developed by SSW with the type designation 2 GU 365/30 “Hertha” were ten-pole separately excited shunt machines with reversing poles, auxiliary series and compensation windings. The traditional tandem arrangement of two rotors on one shaft in one housing was retained. As a result, two "motors" each worked on one shaft, which could be connected both in parallel and in series. This enabled lossless control for two speed levels. Each double machine could also be used as a generator and had a mass of 10,330  kg .

On the test bench, the maximum output of a “Hertha” in parallel at 5500 A power consumption, 360 V voltage and a speed of 1675 min −1 was 1840 kW. In series, the machine was at 1230 min -1 from an output of 730 kW. In generator mode, a current of 4080 A or an output of 1840 kW was achieved on the test stand in parallel connection at 1550 min −1 and 450 V voltage,  and 1040 kW in series connection.

The gear reduction was 5.079: 1, which results in a theoretical maximum speed of 330 min −1 on the propellers. Practically only 316 min were in the original design of U 3506 -1 achieved. The numerous flood and vent openings in the outer shell of the boat caused an unexpectedly strong increase in its water resistance of around 28%. Flood flaps had been dispensed with, as the previous submarines always drove with open flood flaps for safety reasons. The battery voltage also collapsed at high discharge currents of 2 × 5540 A for maximum travel below the planned 2 × 360 V to 2 × 336–305 V. This reduced the output to 2 × 1650–1550 kW. Therefore, the underwater speed originally conceived of 18 kn was not reached at maximum speed.

During a mile journey at a depth of 20 meters, U 3506 reached a speed of 15.93 knots on November 8, 1944 ( Admiralty constant C = 149; definition with speed v in kn, displacement D in ts and power N in PS wave power ). After reducing the flood slots by two thirds and closing the openings in the bridge roof and upper deck, U 3507 was able to achieve 17.2 knots on November 21, 1944 with an output of 3,100 kW (Admiralty constant C = 197). With the initially planned output of 3500 kW and a propeller shape adapted to the lower water resistance, the targeted 18.5 kn would have been attainable. In the final version, the flood slots were reduced by a third to a share of 1.98% of the total surface. With this, U 3507 reached 16.8 knots for 20 minutes and 16.5 knots for 50 minutes on November 30, 1944 (Admiralty constant C = 175). The remaining 15% increase in resistance combined with a rapid dive time of 25 seconds was considered an acceptable compromise. ${\ displaystyle C = {\ frac {v ^ {3} \ cdot D ^ {\ frac {2} {3}}} {N}}}$

When listening to U 2513 at the end of 1946 in the USA, it was found that even at 3 knots of travel with main electric machines, the machine noise was above the flow noise and was around 72 dB. The American dB units, however, obviously do not agree with the German dB values. The noise level was only slightly above the noise level of the listening device used of 70 dB. At 5 kn, 86–86 dB were measured at periscope depth and 73 dB at 60–90 m diving depth. From 7 kn the sound pressure curve flattened to periscope depth, at greater depth it increased more. At 10 kn, 100 dB and 86 dB were measured, at 15 kn both periscope depth and 60 meters depth 104 dB. The values ​​fluctuated slightly by 2–4 dB, depending on the direction of the submarine towards the listening device.

Overall, the submarine was found to be significantly quieter than the quietest American fleet-class submarines. There was no vibration or noticeable increase in noise at high speeds, except when accelerating and braking . At 15 kn the volume corresponded to that of the US boat at 8 kn, at 10 kn that of the US boat at 6 kn.

#### Schleich electric motors

Belt drive of a creep motor

The two creep motors with the designation GV 323/28 also developed by SSW were eight-pole, separately excited shunt motors with auxiliary series winding and reversing poles. They could with 360 V at 140 to 256 A current consumption, 46-83 kW and 285-350 min -1 engine speed, or 120 V at from 74 to 245 A current consumption, from 7.6 to 22 kW and 91 to 190 min -1 engine speed operate. Due to the performance gap, speeds between 4.3 and 5 kn were difficult to achieve.

The creep motors were connected to the propeller shafts via a friction clutch and twelve V-belts with a reduction of 2.68: 1. The friction clutch was locked to the main clutch in such a way that only one clutch could be engaged at a time. The V-belts slipped partially. Nevertheless, the intended maximum speed was reached.

When traveling for miles, the U 3506 achieved 6.1 knots at a propeller speed of 123 min −1 and about 2 × 300 A power consumption at 2 × 360 V. At 82 min −1 propeller speed the speed was still 4.3 knots, at 39 min - 1 2.0 kn.

The U-boats U 2513 and U 3008 , which were taken over from the USA, were subjected to extensive tests. At the end of 1946, the US Navy was unable to locate U 2513 while crawling with listening devices at a distance of 220 m, while merchant ships could still be heard at a distance of 13 km. At 5.5 kn the volume corresponded to that of the quietest American submarine in the fleet class at slowest creep speed (2 kn). The signal mixed with the background noise in such a way that it could no longer be measured. At a depth of over 150 m, passive location was not possible even at maximum crawl speed.

#### propeller

The efficiency of the propellers was 52%. The two main shafts diverged aft at an angle of 3.12 ° from the center of the ship and dropped about 200 mm towards the stuffing boxes. With this, the two propellers with a diameter of 2150 mm turned noiselessly with enough free stroke up to 122 min −1 . Due to the diverging drive shafts, the course could hardly be corrected by different propeller speeds port / starboard when the speed was low or the rudder system failed. The inner propeller had to run faster than the outer one in order to obtain the smallest possible turning circle. A tug aid was useful for mooring and unloading.

### Steering gear

Rudder system of the
Wilhelm Bauer museum boat

Because of the single rudder outside of the propeller streams, the turning circle of 365 to 480 meters was almost twice as large as that of the old types ( Type VII C 230 to 286 meters) the pursuing destroyers . On the surface of the water, the new boats were also cumbersome, and it was unthinkable that escort guards would break through. Inexperienced officers on watch repeatedly caused collisions .

The DE-class escort destroyers, which were particularly suitable for submarine hunts and were delivered in large numbers in the USA from February 1943, were able to travel circles of under 400 yards = 366 meters. In general, however, the destroyers had significantly larger turning circles of 880 yards = 805 meters. The Type  XXI was also able to evade the attacks of submarine fighters when submerged due to its high underwater speed and speed when creeping. The diving depth could be changed relatively quickly due to the higher speed.

### Auxiliary drives (rudder, depth rudder, periscopes, flak towers, muzzle flaps of the torpedo tubes)

The entire hydraulic system, for which there was little experience in submarine use and trained personnel for production, turned out to be too complicated and sensitive. The components for extending and moving the forward depth rudder were located outside the pressure hull, where they were exposed to corrosion from the sea ​​water and could not be repaired during diving trips. In addition, the lines and pistons running there could not be completely sealed. During the tests, this led to the ingress of seawater up to a total failure due to the pumps eating up and a telltale oil trail. The flak towers, which are also located outside the pressure hull, therefore received their own pressure oil circuit at the end of 1944.

### Diving depth

Depth gauge ( Papenberg ) and depth rudder control in the
Wilhelm Bauer museum boat

The Type  XXI was designed for a diving depth of 220 meters and a calculated destructive diving depth of 337.5 meters. The five watertight inner bulkheads were designed to be pressure-resistant to a depth of 50 meters with 1.5 times the safety.

The sheet thickness of the outer, freely flooded outer nave was 5-8 mm. The inner pressure body consisted of aluminum -killed shipbuilding steel St  52 KM with 1.06% manganese  (Mn) - and 0.16% carbon  (C) content. The easily weldable carbon steel St 52 used in German submarine construction until the end of the war had a yield strength of 355  N / mm² and a tensile strength of 520 N / mm².

The upper part of the partially 8-shaped pressure hull had a maximum diameter of 5300 mm, the lower of 3536 mm. At the front end floor in the area of ​​the torpedo tubes, the thickness of the outer plates increased up to 50 mm, in areas with a small pressure body diameter it decreased to 12 mm. In the area of ​​the largest diameter, the thickness of the outer panels was 26 mm for the upper part and 18 mm for the lower part. The flat inner plates between the two printhead shells were 26 mm thick and 2400 mm wide. The flat 1000 mm wide floor of the lower part consisted of 40 mm thick panels. The upper half-shell was reinforced with external ribs, the lower half-shell and the panels in between with internal ribs. The flat rear end bottoms of the two pressure hull shells consisted of 20 mm thick plates, which were reinforced on the upper part with internal ribs and on the lower part with external ribs.

As with the small sister type XXIII, the calculation bases for this new two-circle form of the pressure hull were uncertain. Only the upper part could be interpreted and calculated as a circular pressure body with sufficient accuracy. This was not the case with the lower part because the ribs from the upper part overshot very far and the lower part had floor walls . This therefore had to be designed without a precise calculation basis and its strength tested subsequently.

The first shots were partly dirty rolled . The 32 manufacturers who prefabricated the sections under high time pressure had little or no experience in submarine construction apart from Hannemann & Co in Lübeck. The tolerance of ± 2 mm provided for the pressure hull diameter could not be adhered to and therefore had to be increased to ± 2.5 mm soon after production started. Inspections of the parts at the steel construction companies showed differences of up to 35 mm compared to the drawing dimensions. Additional temperature differences led to larger deviations during assembly despite compliance with the tolerances in the steel construction. In the case of non-matching sections, the pressure hull ends were cut in several places 20 to 30 cm and bent up to the required fit . Only then was it possible to weld them together.

From April 1944, an increase in the carbon and silicon content of steel St 52 was ordered in iron production in order to save manganese. When this arrangement became known in August 1944, cracks were expected to form during welding with a three-month delay . The order was therefore immediately lifted. Since the changeover required another three months, it could not take effect until spring 1945 at the earliest. Welding the new steel with too high a carbon and silicon content later caused difficulties. In this case it was suggested to roll narrower plates. There was a lack of high-quality welding electrodes and experienced welders. Not all welding work was properly completed. In mid-February 1945, welding cracks were found in Type  XXI . It could not be determined whether there was a connection with the material change.

The pressure tests carried out on January 4th to 6th and February 10th to 12th 1945 with models in the pressure tank of the Germania shipyard showed that the lower shell of the 8-shaped pressure hull could not withstand the calculated depth of destruction and was about 10% less firm than that upper. At a simulated depth of around 300 m, a dent began at the end bulkheads of the tub, which led to a break at 315 m. Accordingly, the actual compressive strength of Type  XXI was about 10% below the required value. The head of the Office for Warship Construction , Vice Admiral Friedrich Ruge , noted in his diary under the date March 9, 1945 that sheets were too thin as a result of a design error and “In any case, the diving depth is hardly better than with the Type VII C ”.

During a deep dive attempt by U 2511 on April 8, 1945, increasing crackling noises were perceived when the battery compartment below 160 m was exceeded, which, in the opinion of the experimenter, indicated an impending bulge formation. Later they were explained by harmless plastic deformations of steel parts outside the pressure hull. In addition, a cracked weld seam in the electrical machine room caused water to penetrate, which could be stopped after a short time. Therefore, the deep dive attempt was canceled after three attempts at 175 m. The pillarless torpedo hatch had been subjected to loads of 4000 kg / cm² = 395 N / mm², far beyond the calculation values ​​up to the flow limit . As a result, reinforcements were commissioned for all boats, which led to further delays.

In a subsequent deep dive attempt with U 2506 on April 20, 1945, with precision measuring instruments and technicians on board, the pressure hull noise, which became increasingly dubious with depth, reached 230 m. The measuring devices showed that the critical elastic limit had not yet been exceeded . In the following diving tests with U 2506 on April 26, 1945 and U 2529 on May 8, 1945, the required 220 m were achieved. In the case of U 2529 , slight frame deformations had previously been found on an inner frame under the tower at 140 m . The pressure-resistant inflatable boat containers on the upper deck imploded loudly on both boats at depths between 190 and 230 m.

After the war an American deep diving test with U 3008 reached 727 feet = 221.6 meters. The exhaust pipe of the Junkers compressor, which had no seawater inlet valve, broke. With an angle of attack of 20 ° and a speed of 21 knots, the boat took 30 minutes to come back to the surface.

According to an American report from July 1946, the pressure hull could not withstand the water pressure at great depths and depth charges in the vicinity. The Germans reported to the American experts after the war that the pressure hull failed at a depth of 270 meters simulated with a large model. The British reported pressure hull failure at 240 meters, less than the depth of destruction of conventional German Type VII C submarines . These were designed for a calculated destruction depth of 250 meters and, according to today's knowledge and calculation methods, had a destruction depth of more than 280 meters.

## Use in World War II

U 2511 (center) and other boats arehanded overto the Royal Navy after the surrender in the port of Bergen

Because of the delays in the training of the crews, the mining of the training rooms in the Baltic Sea , a lack of fuel and a multitude of technical problems , the first submarines were only used at the front in the last days of the war. Ground mines detonated next to and behind U 3509 and U 2510 at a distance of about 50 and 30 m respectively. In both cases the pressure hull remained intact, but the outer ship and auxiliary machinery and equipment that were not installed in a shock absorbing manner were severely damaged in some cases . Both boats remained maneuverable, but had to be in their shipyards for a long time. Many other boats were destroyed or sunk in air raids on ports or in the shallow waters of the Baltic Sea, where diving was sometimes not possible.

U 2510 and U 2518 are said to have sighted the Soviet submarine S-13 in the Baltic Sea on January 30, 1945 , which sank the Wilhelm Gustloff a few hours later , but did not attack when visibility was poor. U 2506 , U 2511 , U 2519 , U 3007 and U 3008 were later in the immediate vicinity of the sinking ship, but for reasons of confidentiality and because of the priority of their mission, they were ordered to continue the march westwards without providing assistance.

At the same time as the Hannibal company , several Type XXI submarines were used, contrary to orders, to transport refugees on the Baltic Sea when they were moved west. On April 14, 1945, the combat training of the submarines was finally stopped, with an order of April 26, 1945 the decommissioning and self-sinking of submarines that were not ready for use was prepared. On the other hand, the clear-fronted or conditionally ready-to-use submarines should sail to Norway as a bargaining chip or be used as reserve units.

U 2511 was the first type XXI submarine to sail from Kiel on March 16 or 18, 1945 to the UAK (U-Boot Abnahmekommando) branch in Horten (Norway) , where it arrived on March 23, 1945. His commandant Adalbert Schnee requested that the periscope be repaired because it vibrated heavily even at the slowest speed . In addition, two weakened inner frame webs had to be reinforced before a planned deep dive test. On April 8, it carried out the deep diving test off Kristiansand ( see diving depth ), where it was damaged by a quickly stopped water ingress due to a cracked weld in the electrical machine room, still well above the maximum safety diving depth .

The information and views of the literature sources differ on the further process. It should be noted that the departure and arrival as well as the radio reception often took place around midnight, so that slightly different dates can be reconciled. The war diary of U 2511 can no longer be found today.

U 2511 left Kristiansand on April 17 or 18 to move underwater to Bergen (Norway) . The night before entering Bergen, the sound of another submarine was located in front of the Krossfjord . This was followed all night. Although there were good shooting opportunities according to the values ​​of the SU system "Nibelung", there was no attack due to the risk of confusion with other German submarines. The submarine was the British tapir . She had on April 12 in front of mountains in position 61 °  N , 5 °  O the German Type VII C -Boot U 486 destroyed with torpedoes and was waiting for more incoming and outgoing German submarines. U 2511 arrived in Bergen on April 20 or 21 .

On April 24, U 2511 began the march, but had to return to Bergen after three days due to a diesel damage (connecting rod breakage due to piston water hammer ). U 2511 is said to have been ready to sail again on April 30th . A leakage message deciphered by the British, however, mentions May 3, 1945, 02:30 a.m., which has been adopted from some recent literature sources. A transmission or writing error due to a lost or postponed "0" when deciphering or transmitting the expiry message (date "0230/30" = "April 30th 02:30" or "2300/30" = "April 30th 23: 00 o'clock "instead of" 0230/3 "=" 3 May 02:30 o'clock ") cannot be ruled out. Former crew members specified April 30, 1945 as the expiry date, and Fritz Schäfer also stated 23:00. It is not known whether the boat also left the base area or just the port.

After passing the Marstein lighthouse , U 2511 remained permanently submerged, with occasional snorkeling use. On May 2 or 5, 1945 it had contact with a British submarine fighter association, which it evaded by changing course by 30 ° and moving fast. On May 4 or 5, 1945, the boat is said to have been west of the Faroe Islands - Iceland Passage and at 3 o'clock received the news that submarines were not allowed to attack. Then the march back to Bergen took place. A few hours later, according to the commander Adalbert Schnee and other crew members, there was another contact with an association with the heavy cruiser Norfolk .

The Norfolk ran on May 1, 1945 as part of " Operation Judgment " from Scapa Flow to the sea area west of Narvik . The aim of the operation was to destroy German submarine tenders at Kilbotn and ships anchored at Sandnessjøen . In addition to the Norfolk, the escort aircraft carriers Searcher , Trumpeter , Queen , the light cruiser Diadem , the destroyers Opportune , Scourge , Zambesi , Savage , Carysfort , Obedient , Orwell and the naval tanker Blue Ranger were used. On 5 May 1945 at 16:00 British time off from the carriers 100-150 miles west of the Lofoten aircraft around 16:30 at Kilbotn the German submarine tender Black Watch , the supply ship Senja and type VII -C -Boat U 711 sunk in Kilbotn Bay at position 69 °  N , 17 °  E.

On May 5, 1945 at 8:00 a.m. DBST ( GMT + 2 hours), the Norfolk was around 175 nautical miles west of the entrance to the Vestfjord at position 67 °  N , 5 °  E and sailed at an average speed of 25 knots at the beginning and then 26 knots and heading 205 ° exactly towards the Shetland Islands . It was approaching the sea area that U 2511 also had to cross if it used the suitable Faroe Island Passage on its way back. At 20:00 DBST the cruiser was on position 63 °  N , 1 °  O and changed course slightly to starboard to pass around the Shetlands in the West.

According to the reports, the listener of U 2511 , which was at a depth of 80 meters, detected strong propeller noises from a northerly direction in the early morning hours of 6 May 1945 port ahead. A Suffolk-class cruiser and three backup destroyers were then sighted at periscope depth. The U 2511 initially started at high speed and later at creep speed. The boat submerged the destroyer fuse and then went back to periscope depth. The attack on the 190-meter-long cruiser was canceled by the commander, with certain target dates, shortly before the torpedo shot at a distance of 600 meters to the side of the ship. The boat then went back to depth under the cruiser without being discovered. U 2511 reappeared for the first time on May 6 or 7, 1945 near Bergen at the Marstein lighthouse.

The Norfolk returned to Scapa Flow on May 6, 1945. On May 7, 1945 she left Scapa Flow again with Force 6 for Operation CLEAVER , the goal of which, together with Force 5, was the penetration of surface forces into the Skagerrak and Kattegat . She returned to Scapa Flow on May 10, 1945. On May 14, 1945 she left for Bergen, where she arrived on May 15, 1945.

After the surrender , there was an encounter in Bergen when snow was heard by a British commission on his patrol. She had previously been on the cruiser Norfolk to research the "secrets of the German submarines" in Norway. Only with the presentation of his war diary and the position and speed information entered there was he able to convince the incredulous British that he had approached the unit unnoticed at the firing position. The credibility of his account has also been questioned by some recent literature sources, while other literature sources and crew members confirm this.

U 3008 ("U-Manseck") met a British naval formation with the light cruisers Birmingham and Dido only two hours after receiving the surrender message. Force 5 with the Birmingham and Dido and the destroyers Zephir , Zealous , Zodiac and Zest left Scapa Flow on May 6, 1945 and reached Copenhagen on May 9, 1945. In addition, the periscope observation of an aircraft carrier and some transport ships at some distance is reported.

Both boats broke off the patrol according to the orders without being noticed by the enemy. A third boat, U 2506 , was also on the patrol, but broke it off twice due to technical breakdowns.

U 3503 was on May 6, 1945 at 03:39 at snorkelling trip near Læsø at position 57 °  N , 12 °  O by a Liberator bomber attacked and went with still-running diesel engines on depth. Improper operation, there was strong pressure drop and Verqualmung in the boat with partial failure of the occupation by nitric oxide - poisoning . The boat ran underwater with great speed off Gothenburg and appeared there at 5:00 a.m. Slightdamage from weld cracks on diving cells and fuel oil bunkers , a slight trace of oil and "outside" restricted flights by British bombers were found. The next day the boat was interned in Sweden . Its crew sank it on May 8, 1945. In 1946 the Swedish Navy liftedthe boat, examined it and later scrapped it.

U 3523 escapedthe attack of a Liberator bomberon May 5, 1945 at 1:35 p.m. in the Kattegat east of Anholt during a group march with U 534 , U 3017 and U 3505 by diving early. On May 6, 1945, the boat was located in the Kattegat from 12 miles (about 19 km) distance by a Liberator "G" of the 86th RAF squadron with radar and approached. 18:39 snorkel and periscope of the boat from the Liberator crew were examined and U 3523 with six water bombs at position 56 °  N , 11 °  O sunk. U 3523 was found in April 2018 by researchers from the Sea War Museum Jutland in Thyborøn about ten nautical miles north of Skagen.

U 3503 and U 3523 were used as school boats. No information is available as to whether their snorkels had the camouflage against radar location intended for front boats and whether the water depths allowed normal snorkeling.

## After the war

After the war, some boats were put into service in the navies of the USSR ( U 2529 , U 3035 , U 3041 , U 3515 and two almost finished boats in Danzig) and France ( U 2518 , later Roland Morillot ). U 2513 and U 3008 went to the US Navy , Great Britain ultimately only kept U 3017 . Most of the boats were sunk by Great Britain in Operation Deadlight north of Ireland. Obviously the British in particular had considerable problems with the operation of the Type  XXI (inexperienced crews, battery explosion, etc.), and therefore, but probably also for political reasons, they very quickly sank almost all of the boats that were left to them.

The Americans used the U 2513 and U 3008 for test purposes for a few years, and later, after a leak in the lower part of the pressure hull, the U 3008 as a spare part reserve for the U 2513 . The expansion of the flak towers and the change in the shape of the tower significantly reduced the underwater flow resistance . The outer hull designed for the fast Walter type XVIII boats and a special circuit of the battery cells allowed the U 2513 to briefly increase the underwater speed to 24 knots. Control systems for future nuclear powered submarines could be tested.

An underwater speed of 23 knots was achieved in 1954 with the first nuclear submarine, the Nautilus , even for longer periods of time. The suggestion to connect the aerodynamically favorable "Walter shell" with the nuclear power drive came from the physicist Philip Abelson, who also worked on the Manhattan project . US President Harry S. Truman was on board U 2513 on November 21, 1946 and December 5, 1947 . The Type XXI experience  had a strong impact on the GUPPY program , in which the Americans modernized their submarine fleet after World War II. U 2513 was sunk in 1951 and U 3008 in 1954 during weapon tests. U 2513 is still on the ocean floor to the west of the Key West chain of islands , but Hedgehog bombs with impact fuses that had not detonated during the sinking are still there . U 3008 was later lifted and scrapped.

The last boat that was decommissioned is also the only one used as a museum boat. U 2540 (self-sunk on May 4, 1945, lifted in June 1957) was taken over into the German Navy as Wilhelm Bauer in 1960 , initially remained in service until 1968 and was then used again as a test boat from 1970 to 1982. On December 14, 1983, the newly founded working group “Technikmuseum U-Boot Wilhelm Bauer e. V. “the boat. The boat has been in the German Maritime Museum since 1984 and is still looked after by the association.

The boats U 2505 , U 3004 and U 3506 were lying in the partially destroyed bunker Elbe II of the Howaldtswerke Hamburg at the end of the war . Parts of the boats were dismantled for the Royal Navy in 1949 , but then remained in place. From 1995, as part of the expansion of the Port of Hamburg, the area was filled with sand and converted into a parking lot by 2004. The boats are still lying in the sand below.

Three pressure hulls intended for Type XXI submarines came into the possession of Frankfurt's Volker Possmann in 1946. The former pressure chambers are now used in the Possmann press as tanks for cider.

## Effects on submarine construction

The victorious powers studied the Type XXI boats that were handed over very carefully. Numerous boats of this type sailed under foreign flags for many years. The Type  XXI was trend-setting for the development of new submarines.

## Further developments

Although the German submarine war had turned out to be very costly, the strategic value of the submarine weapon gained more and more importance in the Cold War . On the basis of Type  XXI , submarine types were developed that could complete long and fast underwater journeys at great depths and finally culminated in the construction of nuclear-powered submarines that met the required long diving times and high speeds. The United States led the way in this development, and on January 21, 1954, the first nuclear-powered submarine , the Nautilus , was launched.

The Soviet Union developed the whiskey class and the Zulu class from the  XXI , which were more robust and contained simpler technology.

The French Navy built the Narval- class based on the Type  XXI in the 1950s . Because of their size and large fuel supplies, the boats were used in long-range ocean patrols.

The Oberon- class is a class of British diesel-electric submarines. 13 boats were built for the Royal Navy , 14 more models to Canada (three units, 1965–1968), Australia (six units, 1967–1978), Brazil (three units, 1973–1977) and Chile (two units, 1976) exported. It was designed in the late 1950s and was a modified Porpoise class inspired by the German Type  XXI .

The US Navy was convinced from its own experience of the effectiveness and effectiveness of the submarines and quickly came to the conclusion that submarines would play an important strategic role in the future. Their GUPPY program, which incorporated their experience with the U 3008 and U 2513 , ultimately led to the development of the Albacore , a single-hulled boat with a smooth, hydrodynamically designed, teardrop-shaped exterior. The first operational boats with the new, initially convincing teardrop shape were the American Barbel boats and shortly afterwards the Skipjack class with nuclear drive. In later boats there was a transition from the teardrop shape to the torpedo shape, which is easier to build and dominates today.

## Technical specifications

• Displacement: 1621 tons (above water), 1819 tons (submerged)
• Two-hull construction with partially 8-shaped inner pressure hull and mainly outer ribs between the inner and outer hull
• Length: 76.70 m Lüa (length over all), pressure body 60.50 m
• Width: 6.60 m Büa (overall width), pressure body 5.30 m
• Draft: 6.62 m
• Admiralty Constant C = 149-197
• Clearance height: 12 m
• Speed ​​(max. Reached):
• Above water:
• 15.37 knots with diesel engines (U 3507)
• 17.94 knots with electric motors (U 3005)
• 18.08 knots with diesel and electric motors (U 3507)
• Underwater
• 16.5 knots with electric motors (U 3507)
• 6.1 knots with creep electric motors (U 3506)
• 10.42 knots with diesel engines on a snorkeling trip (U 3503)
• planned diving depth:
• 133 m (immersion depth)
• 220 m (battle diving depth)
• 330 m (destruction diving depth)
• Immersion time 25 seconds with the flood flaps constantly open and with 1.98% immersion slot portion of the surface.
• two 6-cylinder MAN 4-stroke diesel engines M6V 40/46 with supercharging of 2,000  hp /1.470  kW at 520 min -1
• Two SSW -Main electrical machine GU 365/30 in tandem of 2,500 hp / 1,840 kW at 1,675 min -1
• Two SSW-Schleich-electric machines of each GV 323/28 113 hp / 83 kW at 350 min -1 .
• Battery system with 2 × 3 × 62 single cells of the type AFA 44 MAL 740 (six partial batteries in two decks) from Akkumulatoren Fabrik AG (AFA) with a weight of 236 tons and a capacity of 11,300 Ah per cell with a 20-hour discharge.
• Travel ranges (after measurements on U 3507 in the final state):
• Underwater travel with Schleich e-machines
• 487 nautical miles at 3 knots
• 333 nautical miles at 5 knots
• 256 nautical miles at 6 knots
• with main electric machines, underwater travel
• 120 nautical miles at 8 knots
• 79 nautical miles at 10 knots
• 26 nautical miles at 15 knots
• with diesel engines, surface travel
• 15,700 nautical miles at 9 knots
• 14,100 nautical miles at 10 knots
• 10,600 nautical miles at 12 knots
• 5,200 nautical miles at 15.6 knots
• with diesel engines, snorkeling trip
• 15,100 nautical miles at 6 knots
• 10,300 nautical miles at 8 knots
• Fuel oil supply total 296 cubic meters
• Compressed air system (205  atü ; approx. 20 MPa) for blowing out the immersion tanks and fresh air regeneration
• High pressure storage reservoir 7660 liters (1520 m³ air supply) in 23 bottles at 205 atm
• Low pressure 12 atm through pressure reducer to operate the snorkel, torpedoes, etc.
• Generated by two Junkers free-piston compressors (Type 4 FK 115) and an HK 1.5 electric compressor from F. Krupp Germania shipyard . All compressors are designed in four stages. Junkers compressor output 10 l / min at 200 atmospheres with 7.6 kg fuel consumption. Electric compressor output 16 l / min at 200 atm and a filling time of 8 hours at approx. 400 A.
• Pressure oil system (80 atü - approx. 7.9 MPa - for operating the flak towers, periscopes and rudder)
• Total oil quantity 1000 liters
• 2 IMO spindle pumps with 100 l / min delivery rate each,
• 2 spare hand pumps
• 2 air pressure bottles with a capacity of 325 liters each
• Collection and storage container with a capacity of 120 liters
• Bilge system
• 2 double-acting piston pumps with an output of 24 m³ / h against a water column of 300–400 m with a current consumption of 180 A (deep-bed pumps)
• 2 self-priming centrifugal pumps with an output of 70–100 m³ / h against 10–30 m water column with 135 A power consumption (bilge pumps)
• Cooling water pumps in the electric machine room in Lenz switched with an output of 60 m³ / h
• a manual bilge pump for emergencies with an output of 166 l / min with 66 double strokes
• Armament
• 6 bow torpedo tubes with max. 23 torpedoes or 14 torpedoes and 12 TMC or 18 TMB mines (planned)
• 2 × 2 cm twin flak C / 38 (450 rounds / min) with 3450 rounds of ammunition or 2 × 3 cm twin flak  M44 (960 rounds / min) with fire control system and 3800 rounds of ammunition (planned)
• Furnishing
• Air renewal and air conditioning with 4200 m³ / h air circulation
• Active search radar FuMO 65 "Hohentwiel U1" , FuMo 391
• passive FuMB Samos , Cyprus II , Borkum , fly , mosquito
• SU system Nibelungen device from AEG with 5 kW power with 15 kHz pulses with a length of 20 ms in push-pull mode with AS-1000 transmitter tubes , detachment-free sensor base in the foremost part of the tower.
• Balcony device with 2 × 24 sensors in a streamlined Jankowski profile on the keel for listening angles between 150 and 210 degrees, bearing to about one degree at 12 nautical miles for individual sailors and about 60 nautical miles for convoy
• Close listening device (NHG) to locate approaching torpedoes while underwater at 1000–2000 meters. The boat speed was not allowed to exceed six knots when driving over water with diesel in order to enable a timely warning.
• Decoys
• Underwater telephone (UT system, frequency 4120 Hz)
• Gyrocompass Anschütz & Co with six daughters
• 30 kHz Elac echo sounder with two ranges - 25 m and 1000 m
• Hydraulically operated monocular stand tube with 5140 mm stroke length and −10 to +20 degrees tilt angle.
• hydraulically operated, bright binocular aerial target telescope with 6580 mm stroke length and a tilt angle of −10 to +90 degrees
• Safety and rescue equipment
• 11 hand battery lights
• 77 diving rescuers
• 6 carbonated snow fire extinguishers
• 4 inflatable boats, each four meters in length
• a working inflatable boat with a length of 3.3 meters
• 57 one-man lifeboats
• Air traps for emergency exits in the control room, tower, galley and e-machine hatch
• Depth gauges up to 400 meters in the stern and bow areas, in the control center, in the tower and in the diesel engine room
• Target crew: 57 (with on-board doctor or medical officer 58)
• 5 officers (commander, chief engineer, first watch officer (IWO), second watch officer (IIWO), watch or additional engineer (WI or ZI))
• 1 boatswain
• 14 NCOs (2 marine, 8 technical, 2 radio, 2 torpedo)
• 33 crews (12 marine, 16 technical, 3 radio, 2 torpedo)

The crew varied in composition, but also in strength, as, among other things, there was no experience at the front or existing personnel had to be accessed.

• Construction costs: 5.75 million Reichsmarks (3,600 RM / t).

### - Navy

Between 1944 and 1945, 131 Type XXI submarines were launched at Blohm & Voss in Hamburg , AG Weser in Bremen and the Schichau shipyard in Danzig . Of these, 118 boats could still be put into service with the navy before the end of the war . Of these, two boats were lost at sea due to enemy action (air raids) during the last year of the war. Another two boats ran into mines and sank. Another 17 of the boats put into service were destroyed by bomb hits during air raids on ports. Most of the Type XXI submarines in German waters were self -sunk by their own crews in Operation Rainbow at the beginning of May 1945, despite orders to the contrary, as the submarine crews did not trust the lifting of the Rainbow Order. Even largely completed or only slightly damaged submarines in German ports were blown up by the British before they were scrapped. This was possibly intended to prevent the Soviet Union from claiming further Type XXI submarines as spoils of war. The wrecks of the Type XXI submarines lying off the German coasts and in the ports were scrapped in the early post-war years, with the exception of the U 2540, which was later lifted for the German Navy . The eleven boats in Norwegian waters and U 3008 that were still intact at the end of the war were handed over to the Allies according to orders and collected in Lisahally (today Londonderry Port ) in Great Britain . With the exception of a few specimens taken over by the Royal Navy for testing purposes and some of them later given to the Allied navies, these boats were destroyed as part of Operation Deadlight . With ex U 2540 (as Wilhelm Bauer test submarine for the German Navy), a type XXI submarine has been preserved as a museum.

U 2501 Blohm & Voss, Hamburg April 3, 1944 May 5, 1944 June 27, 1944 ? ? Self-sunk on May 3, 1945 in front of the Elbe II submarine bunker in Hamburg
U 2502 Blohm & Voss, Hamburg April 25, 1944 June 15, 1944 July 19, 1944 ? ? sunk 56 ° 06´N 09 ° 00´W on January 1st, 1946 in the course of Operation Deadlight
U 2503 Blohm & Voss, Hamburg May 5, 1944 June 29, 1944 August 1, 1944 ? ? Damaged by an air raid on May 3, 1945 and then self- sunk on May 4, 1945 off the north coast of the Danish island of Fyn
U 2504 Blohm & Voss, Hamburg May 20, 1944 July 18, 1944 August 12, 1944 ? ? self-sunk in the port of Hamburg on May 3, 1945, wreck scrapped
U 2505 Blohm & Voss, Hamburg May 23, 1944 July 27, 1944 November 7, 1944 ? ? Self-sunk on May 3, 1945 in the submarine bunker Elbe II in Hamburg, the parts of the wreck lying above the water were partially demolished and the rest covered with sand in the course of the removal of the bunker.
U 2506 Blohm & Voss, Hamburg May 29, 1944 August 5, 1944 August 31, 1944 ? ? sunk on January 1, 1946 in the course of Operation Deadlight at 55 ° 37´N 07 ° 30´W
U 2507 Blohm & Voss, Hamburg June 4, 1944 August 14, 1944 September 8, 1944 ? ? self- sunk on May 5, 1945 in the Geltinger Bay
U 2508 Blohm & Voss, Hamburg June 13, 1944 August 19, 1944 September 26, 1944 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 2509 Blohm & Voss, Hamburg June 17, 1944 August 27, 1944 September 21, 1944 ? ? Sunk on April 8, 1945 by an air raid near Blohm & Voss in the port of Hamburg
U 2510 Blohm & Voss, Hamburg July 5, 1944 August 29, 1944 September 27, 1944 ? ? self- sunk on May 2, 1945 in front of Travemünde
U 2511 Blohm & Voss, Hamburg July 5, 1944 August 29, 1944 September 27, 1944 ? ? sunk 55 ° 33´N 07 ° 38´W on January 2nd, 1946 in the course of Operation Deadlight
U 2512 Blohm & Voss, Hamburg July 13, 1944 September 7, 1944 October 10, 1944 ? ? self- sunk on May 3, 1946 off Eckernförde
U 2513 Blohm & Voss, Hamburg July 19, 1944 September 14, 1944 September 29, 1944 ? ? see U2513
U 2514 Blohm & Voss, Hamburg July 24, 1944 September 17, 1944 October 14, 1944 ? ? Sunk on April 8, 1945 by an air raid near Blohm & Voss in the port of Hamburg
U 2515 Blohm & Voss, Hamburg July 28, 1944 September 22, 1944 October 19, 1944 ? ? Damaged by mine in the Baltic Sea in December 1944 and then destroyed by Blohm & Voss in an air raid on Hamburg on January 17, 1945, wreck scrapped
U 2516 Blohm & Voss, Hamburg August 3, 1944 September 27, 1944 October 24, 1944 ? ? Destroyed on April 9, 1945 by an air raid in the dock of the Deutsche Werke in Kiel
U 2517 Blohm & Voss, Hamburg August 3, 1944 September 27, 1944 October 24, 1944 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 2518 Blohm & Voss, Hamburg August 16, 1944 October 4, 1944 November 4, 1944 ? ? see Roland Morillot
U 2519 Blohm & Voss, Hamburg August 24, 1944 October 13, 1944 November 15, 1944 ? ? self-sunk on May 3, 1945 in the naval base in Kiel
U 2520 Blohm & Voss, Hamburg August 24, 1944 October 16, 1944 December 25, 1944 ? ? self-sunk on May 3, 1945 in the naval base in Kiel
U 2521 Blohm & Voss, Hamburg August 31, 1944 October 18, 1944 November 21, 1944 ? ? sunk on May 4, 1945 near the lightship Flensburg by an aircraft attack
U 2522 Blohm & Voss, Hamburg August 28, 1944 October 22, 1944 November 22, 1944 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 2523 Blohm & Voss, Hamburg September 6, 1944 October 25, 1944 December 26, 1944 ? ? Destroyed at Blohm & Voss in an air raid on Hamburg on January 17, 1945, wreck scrapped
U 2524 Blohm & Voss, Hamburg September 6, 1944 October 30, 1944 January 16, 1945 ? ? Self- sunk on May 3, 1945 after air bomb damage southeast of Fehmarn
U 2525 Blohm & Voss, Hamburg September 13, 1944 October 30, 1944 December 12, 1944 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 2526 Blohm & Voss, Hamburg September 16, 1944 November 30, 1944 December 15, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2527 Blohm & Voss, Hamburg September 21, 1944 November 30, 1944 December 23, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2528 Blohm & Voss, Hamburg September 25, 1944 November 18, 1944 December 9, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2529 Blohm & Voss, Hamburg September 25, 1944 November 18, 1944 December 9, 1944 ? ? see B 28
U 2530 Blohm & Voss, Hamburg October 1, 1944 November 23, 1944 December 30, 1944 ? ? Destroyed at Blohm & Voss in an air raid on Hamburg on January 17, 1945, wreck scrapped
U 2531 Blohm & Voss, Hamburg October 3, 1944 December 5, 1944 January 10, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2532 Blohm & Voss, Hamburg October 11, 1944 December 7, 1944 not happened - - Sunk at Blohm & Voss in an air raid on Hamburg on December 31, 1944, no uplift due to an air raid on January 17, 1945, wreck scrapped
U 2533 Blohm & Voss, Hamburg October 13, 1944 December 7, 1944 January 18, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2534 Blohm & Voss, Hamburg October 23, 1944 December 11, 1944 January 17, 1945 ? ? self-sunk on May 3, 1945 east of Fehmarn
U 2535 Blohm & Voss, Hamburg October 19, 1944 December 16, 1944 January 28, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2536 Blohm & Voss, Hamburg October 21, 1944 December 16, 1944 January 6, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 2537 Blohm & Voss, Hamburg October 22, 1944 December 22, 1944 not happened - - Sunk at Blohm & Voss in an air raid on Hamburg on December 31, 1944, wreck lifted and scrapped
U 2538 Blohm & Voss, Hamburg October 24, 1944 January 6, 1945 February 16, 1945 ? ? Sunk in front of Arrö on May 8, 1945 , wreck lifted and scrapped in 1948
U 2539 Blohm & Voss, Hamburg October 27, 1944 January 6, 1945 February 21, 1945 ? ? sunk in Kiel on May 3, 1945
U 2540 Blohm & Voss, Hamburg October 28, 1944 January 13, 1945 February 24, 1945 ? ? sunk on May 4, 1945 near the lightship Flensburg itself, wreck lifted in 1957, see Wilhelm Bauer
U 2541 Blohm & Voss, Hamburg October 31, 1944 January 13, 1945 March 1, 1945 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 2542 Blohm & Voss, Hamburg November 13, 1944 January 22, 1945 March 5, 1945 ? ? sunk on April 3, 1945 at the Kiel naval base by an aircraft attack
U 2543 Blohm & Voss, Hamburg November 13, 1944 February 9, 1945 March 7, 1945 ? ? sunk in Kiel on May 3, 1945
U 2544 Blohm & Voss, Hamburg November 15, 1944 February 9, 1945 March 10, 1945 ? ? Sunk on May 5, 1945 southeast of Aarhus , wreck scrapped in 1952
U 2545 Blohm & Voss, Hamburg November 20, 1944 February 22, 1945 April 8, 1945 ? ? sunk in Kiel on May 3, 1945
U 2546 Blohm & Voss, Hamburg November 22, 1944 February 19, 1945 March 31, 1945 ? ? sunk in Kiel on May 3, 1945
U 2547 Blohm & Voss, Hamburg November 27, 1944 March 9, 1945 not happened - - not put into service by a bomb hit on March 11, 1945, self- sunk on May 3, 1945 in Tollerort (Hamburg)
U 2548 Blohm & Voss, Hamburg November 30, 1944 March 9, 1945 April 9, 1945 ? ? sunk in Kiel on May 3, 1945
U 2549 Blohm & Voss, Hamburg December 3, 1944 not happened - - - Launching of the U 2250 in front of it not possible due to a bomb hit
U 2550 Blohm & Voss, Hamburg December 3, 1944 not happened - - - damaged by bombs on March 20, 1945, wreck scrapped
U 2551 Blohm & Voss, Hamburg December 8, 1944 March 31, 1945 April 1945 ? ? Self- sunk on May 5, 1945 in Solitüde (Flensburg) , wreck lying aground in shallow water, blown up by British command on July 23, 1945
U 2552 Blohm & Voss, Hamburg December 10, 1944 March 31, 1945 April 20, 1945 ? ? sunk in Kiel on May 3, 1945
U 2553 Blohm & Voss, Hamburg December 12, 1944 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2554 Blohm & Voss, Hamburg December 14, 1944 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2555 Blohm & Voss, Hamburg December 20, 1944 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2556 Blohm & Voss, Hamburg December 23, 1944 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2557 Blohm & Voss, Hamburg December 30, 1944 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2558 Blohm & Voss, Hamburg February 1, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2559 Blohm & Voss, Hamburg February 4, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2560 Blohm & Voss, Hamburg February 12, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2561 Blohm & Voss, Hamburg February 15, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2562 Blohm & Voss, Hamburg February 24, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2563 Blohm & Voss, Hamburg March 7, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 2564 Blohm & Voss, Hamburg March 29, 1945 not happened - - - between 1946 and 1947 on the blown Blohm & Voss-Helgen
U 3001 AG Weser, Bremen April 15, 1944 May 30, 1944 July 20, 1944 ? November 26, 1944 on May 5, 1945. Wesermünde scuttled
U 3002 AG Weser, Bremen May 23, 1944 July 9, 1944 August 6, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3003 AG Weser, Bremen May 27, 1944 July 18, 1944 August 22, 1944 ? ? sunk on April 4, 1945 by air raid at the Howaldts works in Kiel
U 3004 AG Weser, Bremen June 4, 1944 July 26, 1944 August 30, 1944 ? ? self-sunk on May 3, 1945 in the Elbe II submarine bunker in Hamburg
U 3005 AG Weser, Bremen June 21, 1944 August 19, 1944 September 20, 1944 ? ? self-sunk on May 5, 1945 west of Wesermünde
U 3006 AG Weser, Bremen June 12, 1944 August 25, 1944 October 5, 1944 ? ? self- sunk on May 5, 1945 in the west entrance of the Wilhelmshaven sea lock
U 3007 AG Weser, Bremen July 9, 1944 September 4, 1944 October 22, 1944 ? ? Sunk on February 24, 1945 by an air raid near the AG Weser in Bremen
U 3008 AG Weser, Bremen July 2, 1944 September 14, 1944 October 19, 1944 ? ? see U 3008
U 3009 AG Weser, Bremen July 21, 1944 September 29, 1944 November 10, 1944 ? ? self-sunk on May 5, 1945 west of Wesermünde
U 3010 AG Weser, Bremen July 13, 1944 October 10, 1944 November 11, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3011 AG Weser, Bremen August 14, 1944 October 20, 1944 December 21, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3012 AG Weser, Bremen July 26, 1944 October 13, 1944 4th December 1944 ? ? sunk on May 3, 1945 east of Fehmarn by air raid
U 3013 AG Weser, Bremen August 18, 1944 October 19, 1944 November 22, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3014 AG Weser, Bremen August 28, 1944 October 25, 1944 December 17, 1944 ? ? self- sunk on May 3, 1945 in front of Neustadt in Holstein
U 3015 AG Weser, Bremen August 25, 1944 October 27, 1944 December 17, 1944 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 3016 AG Weser, Bremen September 6, 1944 November 2, 1944 January 5, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3017 AG Weser, Bremen September 2, 1944 November 5, 1944 January 5, 1945 ? ? see N 41
U 3018 AG Weser, Bremen September 18, 1944 November 9, 1944 January 7, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3019 AG Weser, Bremen September 10, 1944 November 15, 1944 December 23, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3020 AG Weser, Bremen October 1, 1944 November 16, 1944 December 23, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3021 AG Weser, Bremen September 26, 1944 November 27, 1944 December 12, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3022 AG Weser, Bremen October 6, 1944 November 30, 1944 January 25, 1945 ? ? sunk in Kiel on May 3, 1945
U 3023 AG Weser, Bremen October 3, 1944 December 2, 1944 January 22, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3024 AG Weser, Bremen October 14, 1944 December 6, 1944 January 13, 1945 ? ? self- sunk on May 2, 1945 in front of Neustadt in Holstein
U 3025 AG Weser, Bremen October 12, 1944 December 9, 1944 January 20, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3026 AG Weser, Bremen October 19, 1944 December 14, 1944 January 22, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3027 AG Weser, Bremen October 18, 1944 December 18, 1944 January 25, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3028 AG Weser, Bremen October 26, 1944 December 22, 1944 January 27, 1945 ? ? sunk in Kiel on May 3, 1945
U 3029 AG Weser, Bremen October 24, 1944 December 28, 1944 February 5, 1945 ? ? self- sunk on May 3, 1945 in the Kiel Fjord
U 3030 AG Weser, Bremen November 2, 1944 December 31, 1944 February 14, 1945 ? ? in on 8 May 1945 Eckernförde Bay scuttled
U 3031 AG Weser, Bremen October 30, 1944 January 6, 1945 February 28, 1945 ? ? self- sunk on May 3, 1945 in the Kiel Fjord
U 3032 AG Weser, Bremen November 9, 1944 January 10, 1945 February 12, 1945 ? ? self-sunk on May 3, 1945 east of Fehmarn
U 3033 AG Weser, Bremen November 6, 1944 January 20, 1945 February 27, 1945 ? ? Self- sunk on May 5, 1945 in the Flensburg Fjord east of Wasserleben
U 3034 AG Weser, Bremen November 14, 1944 January 21, 1945 March 31, 1945 ? ? Self-sunk on May 5, 1945 in the Flensburg Fjord east of Wasserleben
U 3035 AG Weser, Bremen November 11, 1944 January 24, 1945 March 1, 1945 ? ? see N 29
U 3036 AG Weser, Bremen November 22, 1944 January 27, 1945 not happened - - Overturned and damaged in the floating dock of AG Weser on February 25, 1945, sunk by an air raid in the AG Weser shipyard on March 30, 1945
U 3037 AG Weser, Bremen November 18, 1944 January 31, 1945 March 3, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3038 AG Weser, Bremen December 1, 1944 January 7, 1945 March 4, 1945 ? ? sunk in Kiel on May 3, 1945
U 3039 AG Weser, Bremen November 11, 1944 February 14, 1945 March 8, 1945 ? ? sunk in Kiel on May 3, 1945
U 3040 AG Weser, Bremen December 9, 1944 February 10, 1945 March 8, 1945 ? ? sunk in Kiel on May 3, 1945
U 3041 AG Weser, Bremen December 7, 1944 February 13, 1945 March 10, 1945 ? ? see N 30
U 3042 AG Weser, Bremen December 15, 1944 not happened - - - Damaged in an air raid on the slipway on February 22, 1945 , not launched
U 3043 AG Weser, Bremen December 14, 1944 not happened - - - Launch did not take place due to a damaged U 3042 lying in front of it
U 3044 AG Weser, Bremen December 21, 1944 March 1, 1945 March 27, 1945 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 3045 AG Weser, Bremen December 20, 1944 March 6, 1945 not happened - - Sunk by air raid on March 30, 1945 in the shipyard of AG Weser in Bremen
U 3046 AG Weser, Bremen December 29, 1944 March 10, 1945 not happened - - Sunk by air raid on March 30, 1945 in the shipyard of AG Weser in Bremen
U 3047 AG Weser, Bremen January 1, 1945 April 11, 1945 not happened - - self-sunk on May 5, 1945 west of Wesermünde
U 3048 AG Weser, Bremen December 31, 1944 not happened - - - Damaged at the bow in an air raid on the slipway on February 22, 1945, not launched
U 3049 AG Weser, Bremen December 30, 1944 not happened - - - Launch did not take place because the drain is blocked by the damaged U 3048
U 3050 AG Weser, Bremen January 9, 1945 April 18, 1945 not happened - - self-sunk on May 5, 1945 west of Wesermünde
U 3051 AG Weser, Bremen January 8, 1945 April 20, 1945 not happened - - self-sunk on May 5, 1945 west of Wesermünde
U 3052 AG Weser, Bremen January 22, 1945 not happened - - - Heavily damaged in an air raid on the slipway on February 22, 1945, not launched
U 3053 AG Weser, Bremen January 21, 1945 not happened - - - Launch did not take place because the drain is blocked by the badly damaged U 3052
U 3054 AG Weser, Bremen January 27, 1945 not happened - - - Damaged at the stern in an air raid on the slipway on March 11, 1945, was not launched
U 3055 AG Weser, Bremen January 25, 1945 not happened - - - Launch did not take place because the drain is blocked by the damaged U 3054
U 3056 AG Weser, Bremen February 7, 1945 not happened - - - lying unfinished on slipway at the end of the war
U 3057 AG Weser, Bremen February 4, 1945 not happened - - - lying unfinished on slipway at the end of the war
U 3058 AG Weser, Bremen February 17, 1945 not happened - - - lying unfinished on slipway at the end of the war
U 3059 AG Weser, Bremen February 17, 1945 not happened - - - Lying unfinished on slipway at the end of the war, Section 8 not yet welded to the rest of the pressure hull
U 3060 AG Weser, Bremen February 17, 1945 not happened - - - At the end of the war still unfinished in individual sections on slipway, Section 6 received a bomb hit during the air raid on March 11, 1945
U 3061 AG Weser, Bremen February 24, 1945 not happened - - - at the end of the war still unfinished in individual sections on slipway
U 3062 AG Weser, Bremen March 9, 1945 not happened - - - at the end of the war still unfinished in individual sections on slipway
U 3062 AG Weser, Bremen March 7, 1945 not happened - - - at the end of the war still unfinished in individual sections on slipway
U 3501 Schichau-Werke, Danzig March 21, 1944 April 19, 1944 July 29, 1944 ? October 4, 1944 KLA school boat (warship construction training department), self-sunk on May 5, 1945 west of Wesermünde
U 3502 Schichau-Werke, Danzig April 17, 1944 July 6, 1944 August 19, 1944 ? ? Damaged in the stern area in an air raid on Howaldtswerke Hamburg on April 8, 1945, self- sunk on May 3, 1945 off Tollerort (Hamburg)
U 3503 Schichau-Werke, Danzig June 17, 1944 July 27, 1944 September 9, 1944 ? ? Self- sunk on May 8, 1945 west of Gothenburg , lifted by Sweden in 1946 , overturned in floating dock and irreparably damaged, wreck scrapped
U 3504 Schichau-Werke, Danzig June 30, 1944 August 15, 1944 September 23, 1944 ? ? self- sunk on May 5, 1945 in the western entrance of the Raederschleuse in Wilhelmshaven
U 3505 Schichau-Werke, Danzig July 9, 1944 August 28, 1944 October 7, 1944 ? ? April 3, 1945 air raid in Kiel Tirpitzhafen sunk
U 3506 Schichau-Werke, Danzig July 14, 1944 September 9, 1944 October 16, 1944 ? ? self- sunk on May 3, 1945 in the submarine bunker Elbe II in Hamburg
U 3507 Schichau-Werke, Danzig July 19, 1944 September 16, 1944 October 19, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3508 Schichau-Werke, Danzig July 25, 1944 September 22, 1944 November 2, 1944 ? ? Sunk on March 30, 1945 by air raid in the construction port in Wilhelmshaven
U 3509 Schichau-Werke, Danzig July 29, 1944 September 27, 1944 January 29, 1945 ? ? self-sunk on May 5, 1945 west of Wesermünde
U 3510 Schichau-Werke, Danzig August 6, 1944 October 4, 1944 November 11, 1944 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 3511 Schichau-Werke, Danzig August 14, 1944 October 11, 1944 November 18, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3512 Schichau-Werke, Danzig August 15, 1944 October 11, 1944 November 27, 1944 ? ? Sunk in Dock 5 on April 8, 1945 during an air raid on Howaldtswerke Hamburg
U 3513 Schichau-Werke, Danzig August 20, 1944 October 21, 1944 December 2, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3514 Schichau-Werke, Danzig August 21, 1944 October 21, 1944 December 9, 1944 ? ? sunk 56 ° 00´N 10 ° 05´W on January 3, 1946 in the course of Operation Deadlight
U 3515 Schichau-Werke, Danzig August 27, 1944 November 4, 1944 December 14, 1944 ? ? transferred from Oslo to Lisahally on June 3, 1945 , see N 27
U 3516 Schichau-Werke, Danzig August 28, 1944 November 4, 1944 December 18, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3517 Schichau-Werke, Danzig September 12, 1944 November 11, 1944 December 22, 1944 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3518 Schichau-Werke, Danzig September 12, 1944 November 11, 1944 December 29, 1944 ? ? sunk in Kiel on May 3, 1945
U 3519 Schichau-Werke, Danzig September 19, 1944 November 23, 1944 January 6, 1945 ? ? ran into mine on March 2, 1945 north of Warnemünde and sank
U 3520 Schichau-Werke, Danzig September 20, 1944 November 23, 1944 January 12, 1945 ? ? ran into mine on January 31, 1945 northeast of the Bülk lighthouse and sank
U 3521 Schichau-Werke, Danzig September 24, 1944 December 3, 1944 January 14, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3522 Schichau-Werke, Danzig September 25, 1944 December 3, 1944 January 21, 1945 ? ? self-sunk on May 2, 1945 in front of Travemünde
U 3523 Schichau-Werke, Danzig October 7, 1944 December 14, 1944 January 29, 1945 ? ? Sunk by aircraft on May 6, 1945 in the Skagerrak
U 3524 Schichau-Werke, Danzig October 8, 1944 December 14, 1944 January 26, 1945 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 3525 Schichau-Werke, Danzig October 17, 1944 December 23, 1944 January 31, 1945 ? ? sunk in Kiel on May 3, 1945
U 3526 Schichau-Werke, Danzig October 18, 1944 December 23, 1944 March 22, 1945 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 3527 Schichau-Werke, Danzig October 25, 1944 January 10, 1945 March 10, 1945 ? ? self-sunk on May 5, 1945 west of Wesermünde
U 3528 Schichau-Werke, Danzig October 26, 1944 January 10, 1945 March 18, 1945 ? ? self-sunk on May 5, 1945 west of Wesermünde
U 3529 Schichau-Werke, Danzig November 2, 1944 January 27, 1945 March 22, 1945 ? ? self-sunk on May 5, 1945 in the Geltinger Bay
U 3530 Schichau-Werke, Danzig November 3, 1944 January 27, 1945 March 22, 1945 ? ? sunk in the Tirpitzhafen in Kiel on May 3, 1945
U 3531 Schichau-Werke, Danzig November 9, 1944 February 10, 1945 not happened ? ? Transferred to Kiel unfinished at the beginning of March 1945 and sunk in the Tirpitzhafen in Kiel on May 3, 1945
U 3532 Schichau-Werke, Danzig November 9, 1944 February 10, 1945 not happened ? ? Towed unfinished to Brunsbüttel in March 1945 and scuttled off Brunsbüttelkoog on May 5, 1945
U 3533 Schichau-Werke, Danzig November 16, 1944 February 14, 1945 not happened ? ? Towed unfinished to Kiel in March 1945 and sunk in the Tirpitzhafen in Kiel on May 3, 1945
U 3534 Schichau-Werke, Danzig November 17, 1944 February 14, 1945 not happened ? ? Towed unfinished to Kiel in March 1945 and sunk in the Tirpitzhafen in Kiel on May 3, 1945
U 3535 Schichau-Werke, Danzig November 26, 1944 (July 15, 1945 as Soviet booty) ? ? ? Captured by the Soviet Union on Helgen and launched, see TS 5
U 3536 Schichau-Werke, Danzig November 27, 1944 (July 15, 1945 as Soviet booty) ? ? ? Captured by the Soviet Union on Helgen and launched, see TS 6
U 3537 Schichau-Werke, Danzig December 20, 1944 (July 15, 1945 as Soviet booty) ? ? ? Captured by the Soviet Union on Helgen and launched, see TS 7
U 3538 Schichau-Werke, Danzig December 21, 1944 (July 15, 1945 as Soviet booty) ? ? ? Captured by the Soviet Union on Helgen and launched, see TS 8
U 3539 Schichau-Werke, Danzig December 27, 1944 ? ? ? ? Captured by the Soviet Union on Helgen , see TS 9
U 3540 Schichau-Werke, Danzig December 29, 1944 ? ? ? ? Captured by the Soviet Union on Helgen , see TS 10
U 3541 Schichau-Werke, Danzig January 1, 1945 ? ? ? ? Captured by the Soviet Union on Helgen , see TS 11
U 3542 Schichau-Werke, Danzig January 2, 1945 ? ? ? ? Captured by the Soviet Union on Helgen , see TS 12
U 3543 Schichau-Werke, Danzig not
planned for January 29, 1945
? ? ? ? Sections captured by the Soviet Union, see TS 13
U 3544 Schichau-Werke, Danzig not
planned for January 30, 1945
? ? ? ? Sections captured by the Soviet Union, see TS 15
U 3545 Schichau-Werke, Danzig not
planned for February 9, 1945
? ? ? ? Sections captured by the Soviet Union, see TS 17
U 3546 Schichau-Werke, Danzig not
planned for February 10, 1945
? ? ? ? Sections captured by the Soviet Union, see TS 18
U 3547 Schichau-Werke, Danzig not
planned for February 19, 1945
? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 19
U 3548 Schichau-Werke, Danzig not
planned for February 20, 1945
? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 32
U 3549 Schichau-Werke, Danzig not happened ? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 33
U 3550 Schichau-Werke, Danzig not happened ? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 34
U 3551 Schichau-Werke, Danzig not happened ? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 35
U 3552 Schichau-Werke, Danzig not happened ? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 36
U 3553 Schichau-Werke, Danzig not happened ? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 37
U 3554 Schichau-Werke, Danzig not happened ? ? ? ? Sections only partially available, captured from the Soviet Union, see TS 38

### - Royal Navy

Between May and July 1945, the Royal Navy took a large number of German submarines, which had been handed over intact at the time of the surrender of the Wehrmacht , to Lisahally and Loch Ryan in the United Kingdom as part of Operation Pledge . These included the last twelve Type XXI submarines, which had not been sunk and were transferred with the help of remnants of their original crews. The Royal Navy selected some of these boats for prototype tests, which began in the summer of 1945 before the actual division of the captured boats between the victorious powers was clarified. The British gave some new numbers starting with N to the transferred submarines. However, the boats used for trials were not officially put into service either. In addition, the British had such great difficulties with the operation of the Type XXI (mechanical damage, battery explosions, fires, etc.) that shipyard idle times would have been necessary before the tests could be continued and they finally decided to discontinue them completely and to approach the results of the Americans waiting. The official apportionment decision of the Tripartite Naval Commission (TNC) of October 10, 1945 spoke of the twelve Type XXI boats that had come into British hands two to the United States (secretly transferred to America in August 1945), four the Soviet Union and two to the United Kingdom itself. The remaining boats were used as spare parts donors and then sunk in Operation Deadlight . Of the two boats left by the British, U 2518 was initially loaned and then finally given to France , while U 3017 (British N 41) was finally scrapped.

Surname Formerly Start of testing unit End of trial Whereabouts
N 27 U 3515 ? ? ? Delivered to the Soviet Union on November 5, 1945 , see B 27
N 28 U 2529 ? ? ? Delivered to the Soviet Union on November 5, 1945 , see B 28
N 29 U 3035 ? ? ? Delivered to the Soviet Union on November 5, 1945 , see B 29
N 30 U 3041 ? ? ? Delivered to the Soviet Union on November 5, 1945 , see B 30
N 41 U 3017 ? ? ? scrapped at J. Cashmore & Co in Newport on October 30, 1949

### - United States Navy

U 3008 after the end of the war in front of the Portsmouth Naval Shipyard , Kittery, Maine

The United States also received two Type XXI submarines from the inventory of boats that were handed over intact and brought to Lisahally in the United Kingdom . The secret transfer trip to Portsmouth began on August 6, 1945 with the help of remnants of the German occupation. For this purpose, some equipment from other captured Type XXI boats was removed in advance. The reason for the secrecy of the transfer was that they did not want to wait for the official decision on the division of the captured boats, which only took place on October 10, 1945. After detailed investigations and some modifications (expansion of the flak, changes to the tower cladding) in the Portsmouth Naval Shipyard , U 2513 and U 3008 were put into service with the US Navy under their old names . They used this for very intensive tests and finally sank them during weapon tests. While U 3008 was lifted and scrapped, the wreck of U 2513 remained on the seabed.

Surname Formerly Commissioning unit Decommissioning Whereabouts
U 2513 U 2513 August 1946 Operational Development Force in Key West July 1949 Sunk as a target off Key West on October 8, 1951 , wreck is still preserved.
U 3008 U 3008 July 24, 1946 Submarine Squadron (SubRon) 2 in New London ; from March 31, 1947 Submarine Squadron (SubRon) 4 for the Operational Development Force in Key West June 18, 1948 Further tests until 1954, sunk as a target, wreck lifted and sold to Loudes Iron & Metal Co on September 15, 1955, canceled from January 17, 1956

### - Marine national

The French Navy took over - in addition to the Type XXIII boat U 2326 - with U 2518 on February 13, 1946, a Type XXI boat from Great Britain . The boat initially kept its old name and was renamed "Roland Morillot" on April 9, 1951 after a few modifications to the tower. The boat served the French Navy as a test vehicle until the late 1960s.

Identifier Surname Formerly Commissioning unit Decommissioning Whereabouts
S613 Roland Morillot  U 2518 August 20, 1946 ? 17th October 1967 Scrapped in 1969

### - Soviet Navy

In terms of numbers, the Soviet Union was the largest user of captured Type XXI submarines . After the end of the war, she had a total of 24 units as Project 614 in her shipping register. On the one hand, after the end of the war, the Soviet Union received four of the twelve Type XXI boats delivered intact by the Navy from Great Britain . These boats initially retained their British designation such as N 27, but in Cyrillic spelling as н 27 and were later renamed. On the other hand, the Soviets were able to take possession of a Type XXI production facility with the Schichau shipyard during the war by conquering Danzig . Thus the Soviet Union still had almost finished boats lying on the Helgen as well as a whole series of finished sections available. At least four of these boats were still completed and launched after the end of the war. However, by far not all of the available material was used, which is why 24 boats of this type were never actually in service. However, the submarine type XXI had an enormous influence on the further Soviet submarine construction. Almost all diesel-electric post-war designs were derived from the Type XXI, such as Project 613 (whiskey class) and Project 611 (Zulu class) .

Surname Formerly Commissioning unit Decommissioning Whereabouts
UTS 3 (January
9, 1957 ) BSch 28 (September 19, 1955)
B 27 (June 9, 1949)
н 27
N 27 U 3515
? Baltic fleet 1st September 1972 Scrapped in 1973
B 28 (06/09/1949)
н 28
N 28 U 2529
November 5, 1945 Baltic fleet March 25, 1958 already in reserve since December 29, 1955, scrapped
B 29 (06/09/1949)
н 29
N 29 U 3035
November 5, 1945 Baltic fleet March 25, 1958 already in reserve since December 29, 1955, scrapped
B 100 (July 2nd, 1958)
PZS 35 (January 18, 1956)
B 30 (June 9th, 1949)
н 30
N 30 U 3041
November 5, 1945 Baltic fleet September 25, 1959 scrapped
R 1 (03/08/1947)
TS 5 (04/12/1945)
U 3535 ? ? ? Launched as a booty boat at the Schichau shipyard in Danzig on July 15, 1945, sunk as a target on August 7 or 8, 1947, 20 nautical miles northwest of Cape Ristna, Estonia
R 2 (03/08/1947)
TS 6 (04/12/1945)
U 3536 ? ? ? Launched as a booty boat at the Schichau shipyard in Danzig on July 15, 1945, sunk as a target on August 7 or 8, 1947, 20 nautical miles northwest of Cape Ristna, Estonia
R 3 (03/08/1947)
TS 7 (04/12/1945)
U 3537 ? ? ? Launched as a booty boat at the Schichau shipyard in Danzig on July 15, 1945, sunk as a target on August 7 or 8, 1947, 20 nautical miles northwest of Cape Ristna, Estonia
R 4 (03/08/1947)
TS 8 (04/12/1945)
U 3538 ? ? ? Launched as a booty boat at the Schichau shipyard in Danzig on July 15, 1945, sunk as a target on August 7 or 8, 1947, 20 nautical miles northwest of Cape Ristna, Estonia
R 5 (03/08/1947)
TS 9 (04/12/1945)
U 3539 not happened? - - deleted on February 28, 1948, scrapped
R 6 (03/08/1947)
TS 10 (04/12/1945)
U 3540 not happened? - - deleted on February 28, 1948, scrapped
R 7 (03/08/1947)
TS 11 (04/12/1945)
U 3541 not happened? - - deleted on February 28, 1948, scrapped
R 8 (03/08/1947)
TS 12 (04/12/1945)
U 3542 not happened? - - deleted on February 28, 1948, scrapped
TS 13 U 3543 - - - Sections in the conquered Schichau shipyard in Gdansk exist, but no completion, on April 9, 1947 painted and scrapped.
TS 15 U 3544 - - - Sections in the conquered Schichau shipyard in Gdansk exist, but no completion, on April 9, 1947 painted and scrapped.
TS 17 U 3545 - - - Sections in the conquered Schichau shipyard in Gdansk exist, but no completion, on April 9, 1947 painted and scrapped.
TS 18 U 3546 - - - Sections in the conquered Schichau shipyard in Gdansk exist, but no completion, on April 9, 1947 painted and scrapped.
TS 19 U 3547 - - - Sections in the conquered Schichau shipyard in Danzig only partially available, but no completion, painted on April 9, 1947 and scrapped.
TS 32 U 3548 - - - Sections in the conquered Schichau shipyard in Danzig only partially available, but no completion, painted on April 9, 1947 and scrapped.
TS 33 U 3549 - - - Sections in the conquered Schichau shipyard in Danzig no longer exist in their entirety, decision to continue construction at the beginning of 1946, but no completion, painted and scrapped in 1947.
TS 34 U 3550 - - - Sections in the conquered Schichau shipyard in Danzig no longer exist in their entirety, decision to continue construction at the beginning of 1946, but no completion, painted and scrapped in 1947.
TS 35 U 3551 - - - Sections in the conquered Schichau shipyard in Danzig no longer exist in their entirety, decision to continue construction at the beginning of 1946, but no completion, painted and scrapped in 1947.
TS 36 U 3552 - - - Sections in the conquered Schichau shipyard in Danzig no longer exist in their entirety, decision to continue construction at the beginning of 1946, but no completion, painted and scrapped in 1947.
TS 37 U 3553 - - - Sections in the conquered Schichau shipyard in Danzig no longer exist in their entirety, decision to continue construction at the beginning of 1946, but no completion, painted and scrapped in 1947.
TS 38 U 3554 - - - Sections in the conquered Schichau shipyard in Danzig no longer exist in their entirety, decision to continue construction at the beginning of 1946, but no completion, painted and scrapped in 1947.

### - Federal Navy

Wilhelm Bauer at the Eckernförde naval base (1963)
U 2540 / Wilhelm Bauer in Bremerhaven (2004)

The last and longest user of the Type XXI was the German Navy . The U 2540, which was self-submerged at the end of the war near the lightship Flensburg , was lifted in 1957. After restoration and modernization (new tower shape, double machine system of class 201 ) at the Howaldtswerke in Kiel , ex U 2540 was put into service as Wilhelm Bauer in 1960 for the German Navy. Due to the technical changes, the boat was the only unit in submarine class 241 . It was used to test components for the new German submarine classes, as a weapons test platform and as an underwater target for submarine exercises. It was clearly classified as an auxiliary ship with the identification Y880. Most recently, the boat was also under civilian crew and was finally decommissioned in 1982. It is now sponsored by the association "Technology Museum Wilhelm Bauer" in the Old Port as a museum ship in front of the German Maritime Museum in Bremerhaven to visit.

Identifier Surname Formerly Commissioning unit Decommissioning Whereabouts
Y880 Wilhelm Bauer U 2540 September 1, 1960 Wehrtechnische Dienststelle 71 , Eckernförde (1970–1982)
Submarine teaching group , Neustadt in Holstein (1961–1967)
Ship testing command , Kiel (1960)
March 15, 1982 Museum boat in the old harbor in Bremerhaven

## literature

• Eberhard Rössler : submarine type XXI. 4th, 5th, 7th edition. Bernard & Graefe Verlag, Bonn 1986, 2001, 2008, ISBN 3-7637-5806-2 , ISBN 3-7637-5995-6 , ISBN 978-3-7637-6218-7 .
• Eberhard Rössler: History of the German submarine building volume 2. Licensed edition for Bechtermünz Verlag in Weltbildverlag, Augsburg 1996, ISBN 3-86047-153-8 .
• Fritz Köhl: From the original to the model: Uboottyp XXI. A picture and plan documentation. With the collaboration of Eberhard Rössler. Bernard & Graefe Verlag, Koblenz 1988, 3rd edition Bonn 2003, ISBN 3-7637-6000-8 , ISBN 3-7637-6031-8 .
• Eckard Wetzel: U 2540. Karl Müller Verlag.
• David Miller: German submarines until 1945.
• Wolfgang Frank: The wolves and the admiral. 3. Edition. Stable, 1953.
• Siegfried Breyer: 21 years ago - new development direction for submarine weapons. Soldier and Technology, 1966.
• Cajus Bekker : Battle and sinking of the navy. Sponholtz, 1953.
• José Carlos Violat Bordonau: El submarino del tipo XXI. 2006. (Spanish)
• Eberhard Rössler: The sonar systems of the German submarines. 2nd ext. Edition. Bernard & Graefe Verlag, Bonn 2006, ISBN 3-7637-6272-8 .
• Eberhard Rössler: The torpedoes of the German submarines. Mittler Verlag, ISBN 3-8132-0842-7 .
• Ulrich Gabler: Submarine construction. Bernard & Graefe Verlag, Koblenz 1987, ISBN 3-7637-5286-2 .
• Marine-Arsenal, special volume 13. Podzun-Pallas Verlag, 1996.
• Norman Friedman: Submarine Design and Development. Conway Publishing, London 1984, ISBN 0-85177-299-4 .
• Richard Lakowski: SUBMARINE. 1st edition. Military publisher of the German Democratic Republic, 1985.
• Clay Blair : Submarine War. Licensed edition for Bechtermünz Verlag by Weltbild Verlag, Augsburg 2004, ISBN 3-8289-0512-9 .
• Jochen Brennecke : The turning point in the submarine war - causes and consequences 1939–1943. Wilhelm Heyne Verlag, Munich 1991, ISBN 3-453-03667-0 .
• Norman Friedman: US submarines since 1945. An illustrated design history. US Naval Institute, Annapolis MD 1994, ISBN 1-55750-260-9 .
• Harry Schlemmer: From the tower periscope to the optronic mast. History of submarine periscopes at Carl Zeiss. Verlag ES Mittler & Sohn, Hamburg / Berlin / Bonn 2011, ISBN 978-3-8132-0931-0 .
• Technology museum submarine "Wilhelm Bauer". Brief history and technology of the German submarines. 4th updated edition. Technikmuseum U-Boot "Wilhelm Bauer" e. V., Bremerhaven 2007, with the participation of the Military History Research Office , Freiburg im Breisgau
• Eckard Wetzel: U-2540. The submarine at the German Maritime Museum in Bremerhaven. Approved special edition for Technikmuseum U-Boot Wilhelm Bauer e. V., Bremerhaven
• Eckard Wetzel: U-2540. The legendary German submarine type XXI. 1st edition. Motorbuch Verlag, 2012, ISBN 978-3-613-03492-1
• Copies of original documents (reports, service regulations, etc.)

Commons : Type XXI  - collection of images, videos and audio files

## Individual evidence

1. Dieter Hartwig: Grand Admiral Karl Dönitz, Legend and Reality. 2010, Ferdinand Schöningh, Paderborn, p. 122.
2. Eberhard Rössler: The fast submarines from Hellmuth Walter . Bernard & Graefe in the Mönch Verlagsgesellschaft mhH, Bonn 2010, ISBN 978-3-7637-6285-9 (Chapter 7 Unsuccessful efforts for the most modern submarine: The Walter-Type XXVI, page 95).
3. Karl Dönitz: Ten years and twenty days . Memoirs 1935–1945. 10th edition. Bernard & Graefe Verlag, Bonn 1991, ISBN 3-7637-5186-6 (19th chapter, My tasks as Commander-in-Chief of the Navy 1943/45, 1. Problems of naval armament, page 346).
4. Eberhard Rössler: The fast submarines from Hellmuth Walter . Bernard & Graefe in the Mönch Verlagsgesellschaft mhH, Bonn 2010, ISBN 978-3-7637-6285-9 (Chapter 7 Unsuccessful efforts for the most modern submarine: The Walter-Type XXVI, page 99).
5. Eberhard Rössler: Submarine Type XXI . 4th edition. Bernard & Graefe, Koblenz 1986, ISBN 3-7637-5806-2 (Chapter 1.4 Delays and technical difficulties, page 36).
6. Technical University Hamburg-Harburg http://www.tuhh.de/vss (Hrsg.): Festschrift on the occasion of the 100th birthday of Prof. Dr.-Ing. Dr.-Ing. Eh Otto Grim . SERIES OF SHIPBUILDING. Hamburg 2012 (section Prof. Grim and the strength of ships, lecture on the festive colloquium on the occasion of the hundredth birthday of Prof. Dr.-Ing. Dr.-Ing. E. h. Otto Grim, Eike Lehmann, page 8).
7. Hans Jürgen Bohlmann: Calculation of hydrodynamic coefficients of submarines for predicting movement behavior . SERIES OF SHIPBUILDING. Ed .: Technical University Hamburg-Harburg http://www.tuhh.de/vss . Hamburg 1990 (Chapter 3.1.2.2 Hydrodynamic trunk forces according to the wing theory of slim bodies, page 33).
8. Eberhard Rössler: Submarine Type XXI . 7th edition. Bernard & Graefe in Mönch Verlagsgesellschaft mbH, Bonn 2008, ISBN 978-3-7637-6218-7 (Chapter 1.8 Further development and projects, page 104).
9. Eberhard Rössler: History of the German submarine building, Volume 2 . Licensed edition for Bechtermünz Verlag by Weltbild Verlag GmbH, Augsburg 1996, ISBN 3-86047-153-8 (Chapter 11. The electric submarine projects XXIX – XXXI).
10. Eckard Wetzel: U 2540 . The legendary German submarine type XXI. 1st edition. Motorbuch, Stuttgart 2012, ISBN 978-3-613-03492-1 (Chapter VII The Type XXI Construction Program, page 59).
11. Eberhard Rössler: Submarine Type XXI . 7th edition. Bernard & Graefe in Mönch Verlagsgesellschaft mbH, Bonn 2008, ISBN 978-3-7637-6218-7 (Chapter 1.2 The construction program, page 27).
12. Dieter Hardwig: Admiral Karl Doenitz. Legend and reality . Ferdinand Schöningh, Paderborn 2010, ISBN 3-7637-5186-6 (index of footnotes VIII, The Illusion of the »FINAL VICTORY« WITH NEW BOATS, page 343, points 10 & 31).
13. Eckard Wetzel: U 2540 . The legendary German submarine type XXI. 1st edition. Motorbuch, Stuttgart 2012, ISBN 978-3-613-03492-1 (Chapter VII The Type XXI Construction Program, page 68).
14. Eberhard Rössler: Submarine Type XXI . 4th edition. Bernard & Graefe, Koblenz 1986, ISBN 3-7637-5806-2 (Chapter 1.4 Delays and technical difficulties, page 33).
15. Eberhard Rössler: History of the German submarine building. Volume 2. Licensed edition for Bechtermünz Verlag in Weltbild Verlag GmbH, Augsburg 1996, ISBN 3-86047-153-8 (Chapter 10.5 The emergency program and submarine construction at the end of the war, page 412)
16. boards "renewal of air conditioning" and "oxygen system" at the Museum Boat Wilhelm Bauer .
17. a b Ulrich Gabler: Submarine construction . 3rd, revised and expanded edition. Bernard & Graefe Verlag 1987, Koblenz 1987, ISBN 3-7637-5286-2 , p. 111 .
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23. ^ Internet source (company publication) from Carl Zeiss Optronics, 106 years of periscopes for submarine weapons. ( Memento of the original from November 10, 2012 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved April 22, 2011
24. Eberhard Rössler: Submarine Type XXI . 4th edition. Bernard & Graefe, Koblenz 1986, ISBN 3-7637-5806-2 (Chapter 1.1 The way to the Type XXI, page 14 and Chapter 2.61 Flak, page 134).
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26. Clay Blair: Submarine War . US title Hitler's U-Boat War. Ed .: Verlagsgruppe Weltbild GmbH, Augsburg. Licensed edition for Bechtermünz Verlag by Weltbild Verlag GmbH, Augsburg 2004, ISBN 3-8289-0512-9 (preface to volume 1, page 28).
27. Eberhard Rössler: Submarine Type XXI . 7th edition. Bernard & Graefe in the Mönch Verlagsgesellschaft mbH, Bonn 2008, ISBN 978-3-7637-6218-7 (Chapter 1.1 The way to the Type XXI, brief overview of the development of the submarine Type XXI, letter from Walter an Dönitz, page 22).
28. a b
29. Leo Haupts: The University of Cologne in the transition from National Socialism to the Federal Republic . Böhlau Verlag, Cologne, Weimar 2007, ISBN 978-3-412-17806-2 , pp. 360 .
30. ^ Steven P. Remy, The Heidelberg Myth: The Nazification and Denazification of a German University . Harvard University Press, 2002, ISBN 978-0-674-00933-2 , pp. 107 .
31. ^ "Technikmuseum U-Boot Wilhelm Bauer" e. V., Bremerhaven, with the participation of the Military History Research Office, Freiburg im Breisgau (Ed.): Technology Museum U-Boot "Wilhelm Bauer" . Brief history and technology of the German submarines. 4th edition. 2007 (chapter Starting with teething problems, page 86).
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34. M.Dv 381 U-Boating for U-Boat Type VII C 1940
35. Eckard Wetzel: U 2540 . The legendary German submarine type XXI. 1st edition. Motorbuch, Stuttgart 2012, ISBN 978-3-613-03492-1 (Chapter IX Fates of Type XXI U-Boats, pages 96-97).
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38. Technical University Hamburg-Harburg http://www.tuhh.de/vss (Hrsg.): Festschrift on the occasion of the 100th birthday of Prof. Dr.-Ing. Dr.-Ing. Eh Otto Grim . SERIES OF SHIPBUILDING. Hamburg 2012 (section Prof. Grim and the strength of ships, lecture on the festive colloquium on the occasion of the 100th birthday of Prof. Dr.-Ing.Dr.-Ing.E.h. Otto Grim, Eike Lehmann, page 10).
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43. Dieter Hardwig: Admiral Karl Doenitz. Legend and reality . Ferdinand Schöningh, Paderborn 2010, ISBN 3-7637-5186-6 (index of footnotes VIII, The Illusion of the »FINAL VICTORY« WITH NEW BOATS, page 343, items 10 and 31).
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56. ^
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