FuG 200 Hohentwiel


The FuG 200 "Hohentwiel" was a low-UHF band frequency maritime patrol radar system of the Luftwaffe in World War II. It was developed by C. Lorenz AG of Berlin starting in 1938 under the code name "Hohentwiel", an extinct volcano in the region of Baden-Württemberg in southern Germany. The device had originally been entered into a design contest held by the Luftwaffe for the new FuMG 40L. When competitor Telefunken won that contract with its "Würzburg radar" in 1939, the device was shelved.
In 1941, Lorenz started to re-design it for another design contest by the Reichsluftfahrtministerium for an airborne naval search radar. As no special antenna had been specified, initially the simplest possible layout with three transversely-arranged antenna arrays was chosen - the central one for transmitting and two others for receiving, one each to port and starboard of the central transmitting array. Each antenna array possessed sixteen horizontally-oriented dipole elements, in eight sets of two elements each, with each set of four dipole groups vertically stacked comprising each array. For rough guidance, the radio operator had to manually switch the receiving arrays. Later, the device received a motor-driven antenna switch. The received signal strength was displayed on a cathode ray tube so the observer or pilot could roughly gauge the target's heading as 'left', 'right' or 'head on'. The maximum range was 150 km for convoys on the Atlantic. The device was first deployed on Junkers Ju 88, Focke-Wulf Fw 200 and other maritime patrol aircraft and twin-engined torpedo bomber designs, and is known to have been fitted to Heinkel He 111 medium bombers for training purposes, and experimented with on the Heinkel He 177A. In order to avoid capture after a crash, it was fitted with several small self-destruct explosive charges in each of the system's electronics cabinets, which could be triggered by the pilot.
Further details are found in the :file:Hohentwiel FuG200.pdf|air force manual.

Naval use

In 1943, Lorenz was instructed to adapt Hohentwiel for naval use, and soon the Hohentwiel appeared on U-boats, small surface ships, and coastal installations.

There are two U-boat versions of the FuG 200 Hohentwiel used during World War II; FuMO 61 Hohentwiel U and the FuMO 65 Hohentwiel U1. The U-boat versions were easier to maintain and more reliable compared with the other versions. However, the U-boat versions had several disadvantages, the smaller dimension of the antenna and the height of the antenna installation. The antenna was restricted to a smaller dimension as it had to fit within a small area on the port side of the conning tower. In addition, the reduced height of the antenna installation impaired the range. Both U-boat versions had ranges of between for naval targets and between at an altitude of. Resolution was about 3 degrees, and at short range its range accuracy was. Both U-boat versions worked at a frequency 556 MHz and had four rows of six dipoles. Before the U-boat could dive, the antenna needed to be retracted into a well on the conning tower. Both U-boat antenna versions were wide by in height, and total overall dimensions of the antenna frame was.
There are two types of radar transmitter for the FuMO-61 Hohentwiel U and FuMO-65 Hohentwiel U1, the Type F431 C1 and the Type F432 D2. The Type F431 C1 was used on the Type VII and the Type F432 D2 on the Type XXI.

FuMO 61 ''Hohentwiel'' U

The FuMO 61 Hohentwiel U was the marine version of the FuG 200 Hohentwiel used by the Kriegsmarine on Type VII, Type IX and Type XXI U-boats. Beginning March 1944, it began to be installed on Type VII and Type IX.

FuMO 63 ''Hohentwiel'' K

The FuMO 63 Hohentwiel K became available at the beginning of 1944. It was fitted to the foremast and mainmast of surface warships.

FuMO 65 ''Hohentwiel'' U1

The FuMO 65 Hohentwiel U1 was the marine version of the FuG 200 Hohentwiel used by the Kriegsmarine only on Type XXI U-boats. The FuMO 65 Hohentwiel U1 had an updated radar display over the older FuMO 61 Hohentwiel U, it had a Plan position indicator display, known to the Germans as Drauf.

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