Snorkel (ship part)

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Snorkel of the former German U-3008 in US trials, August 1946. The Americans had modified the rear end of the tower to make it more aerodynamic and expanded the anti-aircraft gun.

The snorkel is a hollow mast that supplies diesel engines on board of submarines with fresh air and, depending on the design, removes their exhaust air. Thanks to this technology, diesel-powered submarines do not need to surface to recharge their batteries .

Beginnings in the Netherlands

The idea of ​​snorkeling was generally not new when it was introduced on German submarines in 1943 and was pursued in several navies ( Netherlands , Italy and Japan ) even before the Second World War . In the Dutch Navy, the captain lieutenant Jan Jacob Wichers and JC van Pappelendam dealt with this in particular . In 1927, Wichers received a patent for an air mast that was supposed to guarantee good boat ventilation when sailing underwater at periscope depth. It had no valve because the boat should not dive below periscope depth with it, but should ensure a perfect air supply for the diesel in heavy seas. A snorkel was first used there in 1939 on the O 19 and O 20 of the O-19 class .

The original purpose of the snorkel it was not , to allow the underwater journey with diesel engines (instead of the then slower electric motors). Since the Dutch submarines mainly operated in shallow coastal waters, around 75% of them in overseas colonies (Caribbean, East India and the Far East), they had to prepare for more frequent diving when attacked by ships or aircraft. The frequent diving required good ventilation of the submarine. The harsh weather in the North Sea made it difficult to ventilate the boat well, even when fully surfaced, and to prevent breakers from entering the boat via the navigation bridge. During World War I, the Dutch experimented with tubes for the batteries to supply air to the submarines when they were on the surface or when they were barely submerged. The first boats were fitted with a pair of foldable pipes: one initially to vent the battery compartment from the formation of toxic gases and a second to bring fresh air into the entire boat, including the engine room. On the O-2 , a pipe was arranged in front of and behind the navigating bridge. These pipes allowed the diesel to operate. However, the procedure was dangerous because the valves did not work well, risking water seeping into the battery compartment, where it produced dangerous gases. This semi-submerged boat process has been known as “ trimmed diesel”. These attempts ended in the 1930s. After that, no further tests took place. Instead of using the snorkel, the submarine was driven in the "trimmed diesel" state and supplied with air through the tower hatch.

When sucking in the air for the diesel, the Dutch submarines used a small drainage tank under the snorkel mast, into which additional internal boat air could only get through a special valve. When the snorkel head was flooded by a wave, the snorkel head valve on top of the snorkel mast closed and then did not open again.

Although the Dutch had already used the ventilation pipes in World War I, they were already using the masts even when the navigating bridge was still visible above the surface of the water. That's why the Dutch didn't use a real snorkel.

Japanese snorkel

The Imperial Japanese Navy upgraded their submarine No. 6, the first submarine designed and built in Japan, which entered service in 1906, with a snorkel. This submarine tried its snorkel in 1910, but the opening of the tube came under water, so that the boat filled up and sank with all 16 crew members.

The invention of the Italians

The invention of a modern snorkel is attributed to the Italian major Pericle Ferretti in 1923. An existing ventilation pipe between the two periscopes was used as an air inlet while the air outlet was on the deck. The system worked well, but there were concerns about the visibility of the snorkeling submarine. In 1926 this snorkel was patented, which was called the "Ferretti instrument". Although Ferretti's invention was hailed as a success, the Italian Navy waited seven years before installing the snorkel in the jalea of the new Argonauta- class, as well as in two Sirena- class boats . However, there was no comprehensive introduction because the Italian Navy was concerned about the visibility of the wake of the snorkel mast. The Italian experiment came to an end in mid-1937 when the new commander of the submarines, Rear Admiral Antonio Legnani, ordered the removal and destruction of all snorkels without explanation. Although the Italians had developed a fully functional snorkel, they did not equip their boats with it when they entered World War II in June 1940.

The Dutch and the Italians worked more or less simultaneously on the problem of airing a submerged or half-submerged submarine. The Dutch did not benefit from the invention of the Italians, because they would hardly have given them access to their important naval technology. In addition, the fact that the Dutch system was not applied until a decade after the Italian system suggests that the Dutch did not get any benefit from the Italian invention.

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 expanded, as on the Dutch submarines that had arrived in Great Britain . The German responsible persons at the U-Boot-Abnahmekommando (UAK) had come to the conclusion that this technology was superfluous ballast that could not be used in the rough Atlantic, where a snorkel constantly draws water in high waves.

Turning point in the submarine war of World War II

At the end of January 1943 the battle for Stalingrad was lost; in May the Africa campaign . The German troops and their European allies fell on the defensive on all fronts. In addition, there was a catastrophic turn in the hitherto successful submarine warfare of the German navy. In May 1943 alone, 43 German submarines were sunk. A major reason for this was that the radars of the US aircraft were now equipped with magnetrons , which enabled very short wavelengths and thus a high resolution.

Submarines regularly needed several hours of surface travel to recharge their batteries for underwater travel; they could be located on the surface of the water with surface radar day and night. The loss-making attack of a pack of submarines on the convoy ONS-5 (led by U 650 ) made it clear that the opposing side could now attack submarines more efficiently than before: for every 12 escort ships sunk there were 7 lost submarines. Dönitz concluded: "The location by air and surface vehicles not only seriously affects the immediate fight of the individual boat, it also gives the enemy an apparently well-used means to record the preparatory positions of the submarines and to evade them . You are about to rob the submarine of its most essential property, that it cannot be detected. "

Dönitz then temporarily stopped the submarine warfare against convoys and had most of the submarines recalled from the pack operations. The development of a new generation of submarines that was completely independent of the outside air was not technically possible at the time. Nevertheless, for strategic reasons, the submarine war should not be discontinued without replacement. Therefore, an interim solution was sought that offered itself in the snorkel. In this situation, Hellmuth Walter remembered the Dutch snuivers and took up the idea of ​​snorkeling again in a conversation on March 2 and a letter to Karl Dönitz on May 19, 1943 . First tests took place in the summer of 1943.

Development of the snorkel from summer 1943 until the end of the war in 1945

Delivery of U 889 to the Canadian Navy in May 1945. The folded snorkel on the starboard side in front of the tower can be clearly seen on the upper deck. One of the air lines runs beneath the bridge

Walther's main idea for the successful realization was to suck the air for operating the diesel engines out of the boat interior for up to 60 seconds when the snorkel was cut under the sea. The snorkel should close automatically when flooded and then open again. It should be able to extend and retract like a periscope. Initially, it was expected that periscopes and snorkels could be camouflaged against radar location without great effort. Dönitz supported the idea and had it implemented.

The small U 58 type II C carried out the first tests of the German design in the summer of 1943 in the Baltic Sea. From the beginning of 1944 mainly medium-sized type VII C submarines were equipped with it. When snorkeling, a shallow diving depth had to be adhered to very precisely, as otherwise either the snorkel head would get under the water surface or the boat would break up through the water surface. The first snorkeling systems were folded down by a cable pull. Serious breakdowns when setting up and folding down the snorkel next to the tower or the mechanics of the supply and exhaust air system were initially rather the rule. As of April 1944, related problems were resolved by a hydraulic pressurized oil device.

The maximum speed when snorkeling was limited to five to six knots due to periscope and snorkel vibrations. The vibrations made the extended periscopes almost unusable, the optics of which often shifted. Exhaust gas and spray in front of the periscope obstructed the view . The snorkel head left a long strip of foam on the sea surface, which in daylight made it possible to visually identify snorkeling submarines from aircraft, as did the exhaust plume of the diesel engines. That is why snorkeling was mostly done at night.

If the exhaust 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 their intake ducts inside the boat. This can lead to gasification of the boat and endangerment of its crew. Despite all efforts, diesel exhaust penetrated the interior of the boat, causing headaches for the crew and clouding the view. Operating errors caused several boats to fill up with diesel exhaust fumes and crew members suffered carbon monoxide poisoning . The poisoning became noticeable only hours after the boat had been ventilated and the general weakening of the crew was then so severe that the emergence and opening of the tower hatch was only possible with the greatest expenditure of energy. In addition, the waste from the submarines, which were now constantly submerged, could no longer be disposed of, which further worsened the already bad air inside the boat , which was only rarely renewed .

In order to avoid the enemy radar location, the snorkel was usually driven as deep as possible, below the maximum wave height , so that it was often washed over by the waves . Depending on the sea ​​state , engine power, boat size and pressure drop, this leads to the diesel being switched off and an additional burden on the crew due to air pressure fluctuations of up to 200  mbar inside the boat. In practice, the suction power of the diesel was greater than expected. As soon as the pressure inside the boat had fallen from the normal value of 1020 mbar to 850 mbar, one of the diesels was switched off, and from 750 mbar on, the second was switched off, and electric motors continued. Particularly in the case of operating errors or inattentiveness on the part of the depth oarsmen, even higher pressure drops of up to 400 (500) mbar were not uncommon. The pressure fluctuations led to severe pain, fainting spells and torn eardrums during the subsequent sudden pressure equalization .

Because of its diesel noise a submarine with snorkeling trip was easy with hydrophones on ships or aircraft dropped sonobuoy be located, while the own listening device was almost "deaf". Therefore the snorkeling had to be interrupted at certain intervals to listen. The water resistance of the older boat types optimized for overwater travel, which is greatly increased during underwater travel, almost doubled the diesel consumption compared to surfacing.

This was accepted due to the danger posed by radar-equipped aircraft and surface units. Many commanders initially had problems with this type of dive trip, especially since the valves suffered from leakage problems. The submarine crews almost invariably distrusted the snorkel and hated it when it was used. In May 1944, however, Kaleu Heinz Schroeteler ( U 667 ) was able to suck fresh air into the boat via the snorkel during a chase and finally escape. He then praised the snorkel, but pointed out the need for extensive training.

The submarine leadership was constantly striving to instill confidence in the snorkel. It ensured widespread circulation of an enthusiastic report by Kaleu Rolf Nollmann ( U 1199 ), who had remained constantly under water for 50 days in September / October 1944. Soon afterwards, however, this recommendation was restricted by a sharp warning, since operating errors had resulted in carbon monoxide poisoning of the crews. Dönitz also had another commendable report by Kaleu Schroeteler (now commander of U 1023 ) from March 1945 distributed among the submarine crews.

Little by little, the snorkeling technique in boat use was improved. 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. After completing his patrols from May 28, 1944 to December 5, 1944, the commander of U 170 , Hans-Gerold Hauber, wrote in the war diary that the snorkel had proven itself and that there were no problems with snorkelling or health problems such as poisoning. 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 68 days respectively.

As a rule, the submarines used the snorkel only four hours a day at night to recharge their batteries, and otherwise drove submerged at an economical and very slow speed of 1 to 3 knots with electric motors. Therefore, on average, they could only travel 90 km per day.

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 against 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 in on 5 May 1945 Kilbotnbucht in Norway at position 68 ° 44 '  N , 16 ° 35'  O countersunk type VII C -Boot U 711 was already equipped with the new head valve.

Protection against radar location

Initially, the Allies only had decimeter-wave radar to locate the submarines . 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 AG "Schwarzes Uboot", responsible on the German side for camouflaging submarines, initially developed designs for the submarine tower against active radar location, which absorbed certain frequency ranges , and against active sonar location, the Alberich coating , but both of these suffered from a lack of seaworthiness.

Instead, the snorkel became the most effective antidote to active radar tracking, which is particularly dangerous for the submarines. An undisguised snorkel head still has around 20% of the echo effect of an emerged submarine. After British improvements, from the autumn of 1944 it was also possible to locate small location targets such as snorkel heads or periscopes with radar in the gigahertz range . Under favorable conditions for aircraft, the snorkel detection range decreased to a quarter of the range of a wide-surfaced boat. On the other hand, with radar alone it was not easily possible to distinguish the snorkeling heads of the submarines from other objects floating on the water.

For the “AN / APS-15” or “ASG” radar ( frequency 9.375 GHz = 3.2 cm wavelength , impulse transmission power 24  kilowatts ), allied experiments showed a snorkeling range of 10.5 and 4.1 miles, respectively (around 17 or 6.6 km). In seas of strength 1 and 2, 82 and 67% of the detected targets were snorkels, in seas of strength 3 and 4 it was 55 and 32%, respectively. On the other hand, only an average practical location range of 0.1 miles or 0.6 miles (around 0.2 or 1.1 km) in daylight was derived from statistical deployment data. It turned out that snorkeling was a very successful means of preventing radar location.

To camouflage the snorkel against radar location, Johannes Jaumann and IG Farben developed a coating in the spring of 1944 that reduced the snorkel's reflectivity . This was achieved by building the material from a succession of conductive layers of semi-permeable paper and dielectric backing layers with a very low dielectric constant . The conductivity of the individual layers increases from the outside inwards. This arrangement was later referred to as a shell sump or conductance sump; a wave sump works in a physically similar manner .

Other names are “electrical sump”, location sump or radar sump. Impinging radar waves practically get stuck in the absorbing “shells” of the jacket. The amplitude of the waves becomes gradually weaker and also slower. In the ideal case, the energy of the waves is completely converted into heat, so it is swallowed like in a swamp - hence the name. Initial water and pressure resistance problems were solved with the plastic Zelligelit .

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. It had a residual reflection of less than 10% in the range 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 Jaumann absorber was 68 mm thick and unsuitable for attachment to 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. To camouflage the ball float valve , a sheet metal cone construction ("lampshade") working according to the principle of repellent camouflage was used. It was installed on U 1024 , U 1060 and U 1064 in the summer of 1944 .

Later, the corrugated rubber cover (named after the director of the Heidelberg Institute for World Post and World News , Ludwig Wesch : "Wesch-Matte"), which was founded in 1941, turned out to be a better solution for radar absorption because it was less than 4– 8 mm better suited for the ball float valves. The radar echo decreased in the range from 20 to 3 cm wavelength (1.5-10 GHz) to a residual reflection of 10% on average. In the range 13–2.3 cm = 2.3–13 GHz, the maximum residual reflection at 5 cm (6 GHz) was 30%. 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%. In November 1944, the Wesch-Mat was also approved for use with the ring float valves.

In addition, sheathing of the snorkel head made of wooden slats (the joints of which were carefully covered) and glass wool were used as materials for trial use. The snorkel heads were not invisible, but the probability of being able to detect snorkeling boats was significantly reduced.

With a round antenna ("Bali") mounted on the snorkel, the Naxos radar detector could detect opposing radar devices working in the centimeter range even during snorkeling, so that the boat could go to depth in good time. However, the frequency of the latest Allied radar device, which was developed without the knowledge of the Germans and which worked with a wavelength of 3 cm (10 GHz), was no longer recorded. An observation option for higher-frequency centimeter-wave radar radiation during snorkeling was only provided for follow-up projects in 1945.

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 could no longer be used for this purpose.


Four types from Deschimag were installed :

  1. Type I: supply air connection via flange on tower, rope drive
  2. Type II: Supply air connection via flange on the tower, pressurized oil system with crosshead drive
  3. Type III: supply air connection on the pivot of the snorkel mast, pressurized oil system with crosshead drive
  4. Type IV: extendable snorkel in the tower with built-in air inlet and outlet connection (only types XXI and XXIII ).

Types I – III were stored horizontally outside the pressure hull and folded up for operation in front of the tower, while type IV was extended vertically from inside the boat like a periscope.

With the snorkel from the diving boat to the submarine

The extended snorkel with Bali antenna above the flak on U 3008

With the new submarine types XXI and XXIII, which were already equipped with a snorkel as standard, a new era of submarine warfare was initiated. The snorkel masts that had previously stood next to the tower were no longer erected and lowered, but - as originally planned - extended and retracted from inside the boat. These boats are considered to be the first true submarines in history due to the combination of snorkeling with significantly increased underwater speed and underwater endurance.

The type XXI had a few shortcomings in the snorkel:

  1. The supply air and exhaust pipes were undersized, so that instead of 4000 HP, only 2400 HP diesel output could be achieved.
  2. The snorkel mast showed strong vibrations between 6.5 and 8.5 kn , so that the possible underwater speeds were limited to less than 6 kn (charging with creeping electric motors) and 9-10.5 kn (underwater march).
  3. The extension and retraction caused a lot of noise (95–116 Phon ) , mainly due to the air motor .

Because of the advantages of snorkeling technology, all submarines converted so that today all diesel-electric submarines have snorkels. As a result, fast and deep submarines could be built with multiple tasks.

Individual evidence

  1.  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Internet source for the development of the snorkel, SenW 57STE JAARGANG NR 5 : Aspects of Submarines, Part IV: The Submarine and the Diesel Engine. by Prof. dr ir E. van den Pol. Retrieved August 13, 2011.@1@ 2Template: Dead Link /  
  2. ^ David Miller: "" German U-Boats up to 1945 - A comprehensive overview ", Verlag Stocker Schmidt, Zurich 2000, ISBN 978-3-613-30423-9 , page 122
  3.  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Internet source for the development of the snorkel, SenW 57STE JAARGANG NR 5 : Aspects of Submarines, Part IV: The Submarine and the Diesel Engine. by Prof. dr ir E. van den Pol. Retrieved August 13, 2011.@1@ 2Template: Dead Link /  
  4. ^ Karl Dönitz: 10 years and 20 days , Frankfurt 1963, p. 331.
  5. ^ Karl Dönitz: 10 years and 20 days. Frankfurt 193, p. 346.
  6. Eberhard Rössler: U-boat type XXI. 5th, exp. Edition. Bernard & Graefe Verlag, Bonn 2001, ISBN 3-7637-5995-6 , p. 22 f.
  7. Clay Blair: Submarine War 1942–1945. The Hunted (anthology 2), 2004, ISBN 3-8289-0512-9 , BOOK THREE, EIGHT, Chapter: Enemies with snorkel boats of type VII from Norway. 1944, p. 905.
  8. Jochen Brennecke: Jäger - Hunted. German submarines 1939–1945 . The longest battle in World War II. Unabridged new edition in the Ullstein Taschenbuch, January 2007, 1st edition. Köhlers Verlagsgesellschaft mbH, Hamburg 1956, ISBN 978-3-548-26661-9 (Chapter 22 Chemierat Dr. Cauer - called "Miefdoktor", p. 417).
  9. Blair, as note 4, p. 823.
  10. ^ Clay Blair: The Submarine War 1942-1945. Volume 2: The Hunted. Augsburg 1998, pp. 735, 904 f.
  11. ^ Clay Blair: The Submarine War 1942-1945. Volume 2: The Hunted. Augsburg 1998, p. 955.
  12. Ulrich Lange: On patrol with U-170 and Knight's Cross holder Rudolf Mühlbauer . Self-published, Radebeul 2002, ISBN 3-8311-4135-5 (chapter war diary from May 28, 1944 to December 5, 1944, p. 219, section snorkeling experiences).
  13. ^ Employment of Search Radar in Relations to Enemy Countermeasures
  14. Kühnhold: Ways of electrical camouflage , p. 15 (PDF; 1 MB)
  15. Camouflaging and strong elimination of radar radiation
  16. ^ Herbert Daniel: Electrodynamics - relativistic physics , p. 301.
  17. Schornsteinfeger project, allied report on aspect of German Stealth technology 1944/45
  18. Clay Blair: Submarine War 1942–1945. 2004, ISBN 3-8289-0512-9 , p. 619.
  19. Eberhard Rössler: U-boat type XXIII. 2nd expanded edition. Bernard & Graefe Verlag, Bonn 2001, ISBN 3-7637-5995-6 , p. 168.

Literature (chronological)

  • Richard Lakowski: Submarines. Military publishing house of the GDR, Berlin 1985.
  • Eberhard Rössler : submarine type XXI. 4th, 5th, 7th Ed., Bernard & Graefe Verlag, Bonn 1986, 2001, 2008, ISBN 3-7637-5806-2 , ISBN 3-7637-5995-6 , ISBN 978-3-7637-6218-7 .
  • Ulrich Gabler: Submarine construction. Bernard & Graefe Verlag, Koblenz 1987, ISBN 3-7637-5286-2 .
  • Horst Steigleder: Marine calendar of the GDR 1989, miracle weapons for Dönitz 'submarines. Military Publishing House of the German Democratic Republic, Berlin 1989, ISBN 3-327-00521-4 , pp. 175–176.
  • Eckard Wetzel: U 2540. Berlin 1989/2002, ISBN 3-613-03492-1 .
  • Fritz Köhl, Axel Niestle: From the original to the model. Submarine type VII C. A picture and plan documentation. Bernard & Graefe Verlag, Bonn 1994, ISBN 3-7637-6002-4 , p. 35f.
  • Clay Blair : Submarine War. Licensed edition for Bechtermünz Verlag by Weltbild Verlag GmbH, Augsburg 2004, ISBN 3-8289-0512-9 .
  • Mark C. Jones: Give Credit Where Credit Is Due: The Dutch Role in the Development and Deployment of the Submarine Schnorkel. In: The Journal of Military History, Vol. 69, No. 4 (Oct. 2005), pp. 991-996.
  • Dieter Hartwig: Grand Admiral Karl Dönitz - legend and reality. Ferdinand Schöningh, Paderborn 2010, ISBN 978-3-506-77027-1 .

Web links

Wiktionary: Snorkel  - explanations of meanings, word origins, synonyms, translations