Technology and Operations  
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RE: How did U-Boats spot planes?
Posted by: Ken Dunn ()
Date: September 11, 2001 06:02PM

Hi Keith,

FuMO-29 \'GEMA\'
The first U-boat radar was a converted set originally fitted in surface ships. The U-boat set was designated FuMO-29; it used a fixed array around the front of the bridge, consisting of two horizontal rows of six dipoles each, the upper row for transmitting, the lower for receiving. The transmit antennas were divided into port and starboard groups of three each and were energized in turn, in a very early form of phase-shifting. This gave a coverage of about 10 degrees each side of the bows, which could be increased by altering course or even by turning the U- boat in a complete circle. The set operated at 382MHz and range was approximately 8,200yd (7,500m) against surface targets and 16,400yd (15,000m) against an aircraft flying at a height of 1,640ft (500m). FuMO-29 was installed beginning in 1942 in a few type VIIs (eg, U-230) and a number of Type IXs (eg, U-156). FuMO-29 was often referred to by the crews as the \'GEMA,\' the name of the company that produced it.

The next radar installation involved the same set, but with a new rotatable antenna, which was mounted on the port side of the bridge and retracted into an oblong housing. This was designated FuMO-30. The antenna array consisted of a tubular steel rectangle covered with a wire mesh and with four pairs of dipoles on the front face and two \'figure-of-eight\' antennas on the rear face. This antenna was rotated by a mechanical linkage from a handwheel in the Funkraum (radio room) below.

FuMO-61 Hohentwiel/FuMO-64 Hohentwiel -Drauf
The Kriegsmarine looked urgently for a more effective replacement for the GEMA set and selected the Luftwaffe\'s FuMG-200 Hohentwiel, which was used in the Focke-Wulf FW-200 Condor maritime patrol aircraft as a ship detection set. This was adapted for U-boat use as the FuMO-61 \'Hohentwiel-U’ with a mattress- type antenna 4.9ft (1.5m) wide and 3.3ft (1m) high. There were four rows, each of six dipoles. Operating frequency was 556MHz and maximum range was approximately 12.4 miles (20km) against low-flying aircraft and about 4.3 miles (7km) against ships. The first set was installed in a U-boat in March 1944 and by September, 64 Type VIIs and IXs had been fitted. A slightly modified set - FuMO-64 \'Hohentwiel Drauf\' -was installed in Type XXI boats.

FuMO-391 Lessing
The air-warning set, FuMO-391 Lessing, was developed for use in the Type XXI, where it used the \'runddipol\' antenna atop the schnorchel. Lessing indicated the presence of an aircraft but not its height or bearing. Range on a surfaced U-boat was given as approximately 10,900yd (10,000m) against low-flying aircraft and approximately 18 miles (30km) against aircraft flying at 6,560ft (2,000m). It could also be used when the U-boat was schnorchelling, but the range was much less: approximately 13,200yd (12,070m) for an aircraft at 3,300ft (1,000m).

Source: “U-Boats The Illustrated History of The Raiders of The Deep” by David Miller. ISBN: 1-57488-246-5.


Ken Dunn

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Subject Written By Posted
How did U-Boats spot planes? Keith Wilkinson 09/11/2001 11:10AM
RE: How did U-Boats spot planes? oliver 09/11/2001 03:47PM
RE: How did U-Boats spot planes? Ken Dunn 09/11/2001 06:02PM
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RE: FuMO Ken Dunn 09/11/2001 09:46PM
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RE: SWAMPS walter M 09/21/2001 08:53AM

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