WWII Tech Pubs Briefing

Written by
James Davies

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U7 setting out on her second patrol in September 1939, en route to the Norwegian coast. On this patrol she torpedoed and sank the British ship SS Akenside and the Norwegian ship SS Takstaas, both off Bergen. She made a total of six patrols before retiring to training duties at Pillau, where she was eventually lost, with her entire crew, in a diving accident in 1944.

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Overview

Following the First World War, Germany had been stripped of her Unterseeboot (U-boat) fleet by the Treaty of Versailles. In the years between the wars, whilst the rest of the world argued about arms limitation, Germany quietly began a programme to develop and rebuild her armed forces. The pace of this accelerated with Hitler’s rise to power, and the first German-built U-boat since the end of World War One (the Type II) was laid down on 11 February 1935. Conscious that the world would see this as a major step towards rearmament, Hitler reached an agreement with Britain to build a navy up to 35% of the size of the British Royal Navy. This included a provision to build submarines to match that allowed to the British by international treaty, effectively allowing Germany a submarine fleet equal to the largest in the world. This agreement was signed on 18 June 1935, and the first of the new U-boats, U1, was commissioned just 11 days later.

The Type II U-boat was designed as a coastal boat, too small to undertake sustained operations far away from the home support facilities. Its primary role was found to be in the training schools, preparing new German naval officers for command.

The boat had a single hull, with no watertight subdivision within the single crew compartment. There were 3 torpedo tubes forward (none aft), with space for another 2 torpedoes inside the pressure hull for reloads. 12 mines could be carried in place of the torpedoes. No main deck gun was provided, and a single 20mm gun was provided primarily for defence against aircraft.

Space inside the boat was limited. The two spare torpedoes extended from just behind the torpedo tubes to just in front of the control room, and most of the 24-man crew lived in this forward area around the torpedoes, sharing 12 bunks. Four bunks were also provided aft of the engines for the engine room crew. Cooking and sanitary facilities were basic, and in this environment long patrols were very arduous.

The boat had a diesel-electric propulsion system, with two diesel engines developing 700 hp, sufficient to give a maximum surface speed of 13 knots. 12 tons of diesel fuel was provided, allowing a maximum range of 1,600 miles at 8 knots. When submerged, two electric motors (running off batteries) provided 360 hp, giving a maximum submerged speed of 6.9 knots. The batteries allowed 35 miles submerged at 4 knots. Later variants had larger electric engines, larger battery capacity, and / or increased fuel capacity.

The maximum depth that submarines could dive to cannot be stated with any accuracy. Submarines have a design depth limit (in the case of the Type II this was 150 metres), however in practice the actual maximum depth for each submarine varied, depending primarily on the quality of construction and the degree of damage to the hull. On one pre-war dive U12’s hull cracked at 341 feet, leading to urgent modifications to the Type II fleet.

Advantages of the Type II boat were related to its size, namely its ability to dive more quickly than the larger boats, the low conning tower (making them more difficult to see) and ability to work in shallow water. Disadvantages were also size-related, such as the shallower maximum depth, low number of torpedoes carried, cramped living conditions and low range.

Most of these vessels only saw operational service during the early years of the war (several future ‘aces’, such as Erich Topp and Joachim Schepke, began their careers by scoring well in these boats), thereafter remaining in training bases. Some, however, were transferred to the Black Sea for use against Russia. This involved stripping the boats down to just a hull, transporting them by barge and road vehicle to Linz, and reassembling them to begin work in their new area.

In contrast with other German submarine types, losses were light. This, of course, reflects their use as training boats, although accidents during training accounted for several vessels.

These boats were a first-step towards rearmament, intended to provide Germany with practical experience in submarine construction and operation, and thus to lay the foundation for the larger boats that were to follow. They were limited by their small size, which resulted in a small operational area and minimal offensive capability, however these limitations were a deliberate choice and they were seen to be very effective within their intended role.

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Units

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Specifications

Note 1: Four 20 mm guns (2 x 2) were provided in 1942.

Note 2: Mines are an alternative to torpedoes, not in addition to them

Note 3: Maximum diving depth is approximate

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