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GORDON WILLIAMSON, illustrated by IAN PALMER
U-462, a Type XIV, displays an unusual flak set-up. A Flakvierting has been mounted on a separate pedestal platform separated from the main tower. Note the boat's Octopus emblem.
The standard method of communication between a U-boat and its shore- based command was the short-wave radio, operating on the 3-30 MHz range. Most U-boats were fitted with a combination of a Telefunken receiver, and a 200-watt Telefunken transmitter with a smaller 40-watt Lorenz transmitter as back-up. Once at sea, communication between U-boats utilised medium-wave radio on the 1.5-3 MHz range. Once again, the equipment was manufactured predominantly by Telefunken. Finally, signals sent to U-boats whilst submerged required the use of very long wave signals on the 15-20 MHz range. These required an enormously powerful transmitter on land, but were the only sure way of making contact with a submerged boat. These signals were also received on the same Telefunken equipment as the medium-wave signals.
Basic radar equipment began to be installed on U-boats in 1940. The earliest operational type was the FuM029 (Funkmessortungs Gerät). This was predominantly used on the Type IX, but a few Type VIIs were also fitted with this equipment, easily detected on photographs because of the twin horizontal rows of 8 dipoles on the upper front part of the conning tower. The top row were transmitters and the lower row receivers. An improved version, FuM030, was introduced in 1942 in which the tower-mounted dipoles were replaced by a so-called retractable 'mattress' antenna which was housed in a slot in the tower wall.
This equipment was only partially successful in detecting other ships due to the very low position of its mounting in respect to the ocean surface (on surface ships, the radar is usually mounted high up on the mainmast or bridge top). Interference with the radar signal by the ocean surface in heavy weather meant that enemy ships might be detected visually before being picked up on radar. An improved version, the FuMO61, was little better in this respect but did provide good aircraft detection results.
U-462 seen during a mid-ocean refuelling operation. The fuel pipe can be seen trailing from her stern.
A new type of radar, the FuMB1 (Funkmesserbeobachter), also known as Metox, was introduced in July 1942. This equipment was used in conjunction with an extremely crude wooden cross-shaped antenna strung with wire and known as the 'Biscay Cross'. This antenna had to be rotated by hand. Unfortunately, the Metox's own emissions were detectable by Allied radar detection equipment, leading them straight to the U-boat. A later, improved version, the FuMR9 Zypern, was also found to be detectable by the British H2S radar detection system. Not until the FuMB10 Borkum set did the U-boat have a radar detection system that was not itself detectable.
This still left the problem of the existing equipment not covering the full radar spectrum, a problem eventually solved in November 1943 by the FuMB7 Naxos. Naxos and Metox used together finally gave the
U-boats excellent all-round radar detection capabilities. The range of capabilities of Naxos and Metox were finally combined in a single system with the introduction of the FuMB24 Fliege and FuMB25 Mäcke systems in April 1944.
A Type IIB is beginning its dive. As the boat slips below the surface, the diesel air intakes and exhaust vents are automatically sealed as the engine shuts down and the electric motors take over. Note the pedestal fitted to the foredeck for the 2 cm flak gun.
The earliest form of sound detection equipment used on U-boats was the Gruppenhorchgerät (GHG) installed in early vessels. The sound detectors were installed in the hull on either side of the bow, so that sound detection was only truly accurate when the boat was abeam of the vessel being detected. Improved sound detection came with the Kristalldrehbasis Gerät (KDB) in which the sound detection array was contained in a rotating, retractable mount set into the foredeck. This was the system carried on most Type VII vessels. A number of Type VIIs were also equipped with the so-called Balcon Gerät (Balcony Apparatus) set into a 'balcony'-shaped faring in the lower part of the bow. This gave a far better effective field than either the GHG or KDB systems.
Three Type IIBs of the Weddigen Flotilla, tied up to their support ship, the Unterseebootsbegleitschiff Saar. Prior to the outbreak of war, all boats carried their number painted in black or, most commonly, white on the side of the tower, as well as on a small plaque on each side of the bow.