Four-poster bed method

The four-poster bed method was a method of guided night hunting in World War II , in which radar devices were used on the ground to guide night fighter aircraft. In the fixed four-poster bed positions, anti-aircraft floodlights and anti-aircraft batteries were also used to support the defense against bombers. This strategic defense facility lost a large part of its effectiveness and importance when the RAF began in mid-1942 to concentrate the stream of bombers on a small width and thus "flood" the four-poster bed positions, which had only a small depth. In addition, from 1943 there was the intensive use of radar jamming measures ( Düppel ), which made guidance from the ground very difficult. Thanks to the development of high-performance on-board radar devices, a modified four-poster bed method with guidance via VHF radio could also be used to a lesser extent afterwards.

The Allies also referred to the series of four-poster bed positions as the Kammhuber Line after the organizer Major General Josef Kammhuber . When fully expanded in 1943, the positions extended along most of the western border of the German occupied territory from Denmark to southern France and reached a length of over 1,000 kilometers. Further expansion was stopped when the effects of the Window radar jamming measures became apparent in August 1943.

history

Prehistory and beginnings

The first night attack on a German city (Mönchengladbach on May 11th / 12th, 1940), despite the relatively minor damage caused, led the Air Force High Command to increase the urgency of night hunting. The planning staff of the Reich Aviation Ministry (RLM) based its planning of the appropriate measures on a report by the then 29-year-old commander of destroyer group I. / ZG 1 , Captain Wolfgang Falck . His proposal was based on his own experience of night bomber attacks on his group's berth in Aalborg (Denmark). With a specialist from a coastal radar unit, he worked out a concept that laid the foundation for night hunting procedures in the years that followed. It essentially provided that a fighter circled in a given space in order to be guided by a radar station to the incoming enemy aircraft in the event of an emergency. In order to put his theory to the test, he and five experienced pilots set up what he called a twilight readiness riot. In an attack by the 61st Squadron of the Royal Air Force on the night of April 30th to May 1st, 1940, three pilots intercepted bombers departing from the airport, but no kills were achieved. However, this proved that the concept could be implemented in principle.

After the campaign in the west , Falck was ordered to Düsseldorf with the 2nd and 3rd squadrons of I./ZG 1 on June 22, 1940 to set up the first night fighter squadron (NJG 1). On July 17th, the 1st Night Hunting Division was set up and the command post was set up in a castle near Utrecht . The 43-year-old Major General Josef Kammhuber was appointed as division commander. This was originally an infantryman in the First World War , who then served in the Reichswehr before joining the Air Force in 1933. Before his appointment, Kammhuber had been commodore of Kampfgeschwader 51 (KG 51), but his experience in the RLM General Staff was probably the decisive factor for his appointment.

Until July 1940, the technical conditions for night hunting were still very inadequate. The aircraft used were standard Bf 110 day destroyers painted black , which had neither special radio equipment nor flame suppressors on the exhaust pipes. The lack of any operational guidance through ground stations caused Falck to relocate a regiment of flak searchlights from the Ruhr area to the vicinity of Münster , along the route of the British bombers' approach. The I./NJG 1 was relocated to Bönninghardt behind the flak headlight belt . In response to the keyword “pheasant”, which was used to alert the Bf 110 after the incoming bombers had been recorded by the Freya coastal radar stations, they started and circled over a radio beacon behind the headlights. If the moving headlights formed a pyramid, indicating the detection of a bomber, the waiting fighter was free to attempt an attack at his own discretion. An anti-aircraft defense did not take place here in order not to endanger own machines. This practice was called light night hunting . The approach to the bomber had to be done quickly, as it took only about three minutes to fly through the headlight belt and the bomber then had the dark, safe area.

Despite these difficulties, on July 20 and 22, 1940, Lieutenant Werner Streib managed to shoot down two Armstrong Whitworth Whitley from the 51st and 78th Squadron. After more British losses occurred, the bombers simply flown around this isolated belt of headlights. As a countermeasure, all that was left to do with Falck was to move individual batteries to the places where they had been entered the previous night. However, the success was small as it took four weeks to the next kill.

Canopy bed construction

Four-poster bed night hunting zones, development status in winter 1941/42

Map of the four-poster bedding (night hunting room) 6B (see general map above) in the Hasselt area (Belgium)

Guiding a night fighter by ground penetrating radar was a difficult problem to solve in 1940. The only electronic "eyes" were the coastal radar stations "Freya". With a range of 160 km, these could be used as an early warning device, but were not suitable for guiding hunters. On the one hand, this was due to the insufficient spatial resolution, but above all to the lack of height information. As a first remedy, on September 7, 1940, a special air communication unit was set up in Nunspeet on the southern IJsselmeer . With the help of a device developed and stationed there, which expanded the Freya to include a device for determining heights (Freya elevator), the first shooting was achieved on October 16, 1940, which was entirely based on a ground guide. Lieutenant Ludwig Becker (4./NJG 1) shot a Vickers Wellington with his Dornier Do 17Z-10. Kammhuber was now convinced that a "dark night hunt" (DuNaJa, without the help of flak headlights) is possible. He then expanded the one test position to a series of overlapping stations on the North Sea coast from Denmark to the canal.

By the late summer of 1941, the DuNaJa was responsible for around 50 kills, while the "Helle Nachtjagd" (HeNaJa) still achieved twice the number of kills. In the final stage, 16 DuNaJa zones were set up as the front line of the nocturnal defense. Although their importance declined sharply from around the beginning of 1942 with the spread of on-board radars, the Freya remained a useful addition to the defense of the Reich until the end of the war.

In the bright night hunt, attempts were made to couple the flak headlights with a Freya device (parasite device). What was missing, however, was a real precision radar with a range of about 60 km. The first attempts with the Würzburg A device (3-meter parabolic mirror) were not very successful. Only with the development of the Würzburg giant was the basis for Kammhuber's entire defensive strategy laid. The headlight regiments were divided into their individual batteries, these were positioned in individual "boxes" at about 40 km intervals. Each box also contained three separate radars: a Freya for early warning and overall surveillance and two Würzburg giants, one of which was used to track the bombers and the other to guide the night fighter. All position reports were sent to a command post and were manually coordinated on an evaluation table (the forerunner of a “Seeburg” table). A lead officer then introduced the German night fighters to the RAF bombers by radio. This system was called the "canopy bed" by the Air Force and was the core of the defense chain called the Kammhuber Line by the Allies. The number of boxes increased until mid-1942 when an uninterrupted chain was created that stretched like a "dog's leg" from Denmark to France.

Improved four-poster bed

Using the capabilities of the " Gee device " and the increasing Allied bomber production, Harris planned to "flood" the four-poster bed positions in a narrow approach area. The two Würzburg giants in one position were unable to bring more than one night fighter close to a bomber at the same time. Intercepting a bomber took about ten minutes on average, during which all others could fly through the box unmolested. In the first 1000 bomber attack on May 30, 1942 , which was aimed at Cologne, this new tactic seemed to work despite a total loss of 41 bombers, of which 18 bombers fell victim to night fighters. Kammhuber reacted to these challenges of the British bomber power strategy by strengthening the four-poster bed positions by providing greater depth staggering. Instead of a box, the bombers should be forced to fly through a series of boxes. Kammhuber also called for the monthly output of Würzburg giants to be doubled from 30 to 60, but by September 1942 to deliver 600 devices. The four night fighter squadrons were also to be doubled to eight. The OKL, on the other hand, considered the planned slow expansion to be sufficient, not least because the use of on-board radar (Lichtenstein B / C) gradually seemed to pay off.

The four-poster bed procedure was improved and expanded as a measure against the incoming flights concentrated on a narrow section. This enabled the activities of three neighboring boxes to be combined during use. Each box overlapped its neighbor by 25%. So it was possible to lead three hunters at the same time in an area that corresponded to half a standard box. But this only at the expense of the two neighboring boxes, 75% of which could not be covered. In some of the attacks by Bomber Command in the summer of 1942, these emergency measures proved to be quite effective. The increasing experience of the crews with the Lichtenstein on-board radar devices also contributed to a growing number of kills. Half of all radar approaches resulted in a launch. The expansion of the “Freya” coastal early warning stations through the establishment of “ Wassermann ” and “ Mammut ” stations, which enemy bombers could already detect over England, improved the effectiveness of the four-poster bed positions.

Due to the massive drop of 40 tons of window strips during the attack on Hamburg on 24/25. In July 1943, the failure of the radar guidance resulted in a complete “blinding” of the four-poster bed system. Actually only proposed by Hajo Herrmann to supplement the four-poster bed system, the “wild boar” night hunt, which managed completely without radar guidance, offered a way out of the misery. At the same time, Colonel Viktor von Lossberg suggested that twin-engine night fighters could also be involved in a modified form of the Wild Sau. For this purpose, they should first be directed to the area of the strongest window disruptions using the Luftwaffe's Y-procedure , on the assumption that the approximate flight route of the enemy bombers can be identified without knowing the exact position of the enemy bombers. Once there, the hunters were supposed to try to use the on-board radar to locate the bombers using this procedure, known as the “ tame pig ”. The success of these measures became apparent in August 1943, when together with Wilde and Zahme Sau 202, and with the four-poster method, only 48 kills were achieved.

As a countermeasure, the Bomber Command began to split off smaller formations - mostly consisting of Mosquito high-speed bombers - from the previously compact bomber streams to deceive the Y-system. German attempts to adapt the radar equipment to the new conditions did not lead to great success. Neither Würzlaus nor Nuremberg were successful. The improved Lichtenstein on-board radar SN-2 was in development and was only manufactured in large series from the end of 1943. Kammhuber was ousted by being commander of the XII. Fliegerkorps was replaced by Major General Josef "Beppo" Schmidt, formally remained General of the Night Hunting for a few weeks before he was transferred to Scandinavia as Commander of Air Fleet 5 .

In 1944, the use of the four-poster bed method went back to a greatly simplified version, which was now referred to as regional night hunt. Here, the fighters circled in the known entry routes of the RAF, where they were guided by VHF radio messages. The Wilde-Sau method, on the other hand, was referred to as object night hunting.

Combined night hunting rooms were set up for the special protection of larger cities . These usually consisted of three four-poster bed positions with combined light and dark night hunting zones. Incoming bombers were illuminated with headlights and first fought by night fighters, after which the flak received precise target data and was able to fire precise barrages.

Process of a four-poster bed use

The responsibility for all operations in a four-poster bed deployment was in the hands of the Jägerleitoffizier (JLO) of an air intelligence regiment, who was operating the one deployable aircraft in a four-poster night fighter room. As early as 1941, the Freya stations stationed furthest to the west were able to locate the RAF aircraft if they were still in British airspace. If aircraft flying in were detected, the report was sent to a night fighter unit in the expected entry route. The night fighter that had taken off tried to reach its operational altitude as quickly as possible, and shortly after take-off the aircraft crew and the control officer established radio contact. At the same time, the officer of the Würzburg radar responsible for guiding the fighter was instructed to record his own aircraft and report his position to the command post of the night fighter leader. By means of an optical device, the hunter's position could be made visible as a green point of light for the control officer on the glass plate of a so-called Seeburg table . As soon as the Freya radar reported that the enemy aircraft would soon be within the detection range of the Würzburg radar, the fighter pilot received the course information to get in front of the aircraft to be intercepted. During this maneuver it was very important that the fighter pilot did not leave the detection range of the Würzburg radar, as otherwise he would no longer have been visible to the chief officer.

On the basis of the Freya data, the second Würzburg radar has now been informed of the bomber's course. As soon as it came within range of this radar, the measurements began and a red point of light appeared on the Seeburg table. The fighter control officer used this information to transmit the course, speed and altitude of the aircraft to be intercepted to the fighter and gave the fighter instructions on how to correct his own course in order to establish visual contact with the bomber. However, no measurements could be made when flying directly over the radar systems. As long as the night fighters were not yet equipped with on-board radar, the interception success was mainly based on the experience of the JLO. A high level of interception security could only be achieved with the introduction of the Lichtenstein on-board radar , especially in the SN-2 version.

Web links

literature

Gebhard Aders : History of the German night hunt , Motorbuch Verlag, 1977, ISBN 3-87943-509-X

John Weal: Luftwaffe Nachtflieger, Part 1: 1939-Spring 1942 , Wings of Fame, Vol. 14 (1999), pp. 104-123.

John Weal: Luftwaffe Nachtflieger, Part 2: May 1942-May 1945 , Wings of Fame, Vol. 15 (1999), pp. 102-124.

Jerry Scutts: Osprey Aircraft of the Aces No. 20, German Night Fighter Aces of World War 2 , Osprey Publishing, 1998, ISBN 1-85532696-5 .

David P. Williams: `` Nachtjäger - Vol. One (Luftwaffe Colors) '', Luftwaffe Night Fighter Units 1939-1943, Ian Allan Publishing, 2005, ISBN 1-903223-53-9

David P. Williams: `` Night Fighter - Vol. Two (Luftwaffe Colors) '', Luftwaffe Night Fighter Units 1943-1945, Ian Allan Publishing, 2006, ISBN 1-903223-54-7