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GORDON WILLIAMSON, illustrated by IAN PALMER
Three principal types of directional control were developed in the Second World Wan all of which were used with some success after teething problems were eliminated.
The original FaT design was first used on the G7a(TI). It was an excellent anti-convoy concept in that the torpedo, instead of making a direct line to the target, ran in an 'S' configuration through the convoy until finding a target. The required launch position was alongside die convoy. A further development, the FaTII, was based on the G7e(TII).
This torpedo, similar in concept to the FaT, allowed the U-boat to attack the convoy from any angle rather than having to attain the ideal launch position alongside the convoy.
This torpedo, based on the G7e, had acoustic detectors, which homed in on the sounds of the target vessel's propellers. It was, however, prone to premature detonation when passing through turbulent waters, such as the wake of a ship. This torpedo had a range of 5.75 kilometres at 24.5 knots.
This was a development of the basic Zaunkdnig, which had the acoustic detectors tuned to specific frequencies of ship's propellers to avoid premature detonation, and was to be used with some success as an anti-escort weapon, fired from the stern torpedo tube against pursuing escort vessels.
U-462, a Type XIV tanker, returns to port after a mission. Her fuel bunkers depleted, she sits high in the water showing the huge bulk of her hull.
There were a number of developments in submarine-1aunched mines during the Second World War, of which the four most significant were the TMA, TMB, TMG and SMA.
This mine was for use in depths of up to 270 metres and carried an explosive charge of some 215 kilos. Launched through the torpedo tube, it was of the same diameter as the standard torpedo, but shorter at 3.4 metres, so that two could be launched from each tube at the same time.
Designed for use in shallow waters of up to just 20 metres, the TMB was shorter again, at just 2.3 metres, but carried a 580-kilo charge. Three could be carried in and launched from each tube.
This was a development of the TMB, larger at 3.3 metres in length, but with a 1,000-kilo charge. Two could be carried in and launched from each tube.
This mine was designed for dropping from a vertical mine shaft in specially designed mine laying boats rather than launching from the torpedo tubes. It was 2.15 metres in length and carried a 350-kilo charge. It could be used in waters up to 250 metres in depth.
All of the U-boat types covered in this volume were diesel powered, with additional electric motors coupled onto the same propeller shafts as the diesels. Diesels were used for surface running, and electric motors for running submerged.
Crewmen on board U-461, a Type XIV, observe as mid-ocean refuelling begins. One submarine is being refuelled whilst another waits its turn. The fuel pipe and valves can be seen to the left of centre.
Not until the advent of the snorkel was it possible for a U-boat to charge its electric motors by running its diesels whilst still at periscope depth. The snorkel was a simple 'breathing' tube that allowed air to be drawn into the boat whilst submerged. Its head contained a simple flap mechanism with a flotation ball. The rise of a wave against the head would lift the ball, sealing the tube and preventing the ingress of water. The main problem with the snorkel arose when the boat's depth was not correctly monitored and it slipped below periscope depth, or in heavy seas when the flap remained closed more often than open. When no air was being taken into the boat, the engines would draw their air from the boat's interior, creating a partial vacuum and debilitating the crew.
The diesel engines driving each propeller shaft were mounted on extremely robust foundations. Almost completely filling the engine room space, only a narrow access passage between the two allowed movement through the compartment. Serving in the confines of the engine room was hot, smelly and unpleasant. Many mechanical breakdowns were extremely difficult to work on due to the cramped space.
The Type VIIA was outfitted with two six-cylinder Maschinenfabrik Augsburg-Nürnberg (MAN) or Germaniawerft diesels, each developing 1,160 bhp. Coupled onto the same shafts were two 375 hp electric motors that, when the clutch was disengaged and they were rotating freely whilst the diesels drove the boat, acted as generators to recharge the batteries. Principal suppliers of electric motors for U-boats were Siemens, AEG and Brown-Boveri. Later Type Mis (B-F) used two 1,400 bhp diesels paired with two 375 bhp electric motors.