Type VII submarine

The Type VII was a class of medium attack U-boats built for Nazi Germany's Kriegsmarine from 1935 to 1945. Derived from the World War I design of the Type UB III and the Vetehinen class built for Finland, the Type VII was designed for attacking the North Atlantic convoy lanes and formed the backbone of the German effort in the Battle of the Atlantic during World War II. The Type VII came in several subtypes: The first subtype VIIA had some shortcomings in handling, range and armament, and these shortcomings were addressed in the subsequent VIIB. When more space was needed for a sonar, a slightly enlargened version VIIC was put into production. The fourth subtype VIIC/41 featured a strengthend pressure hull for improved diving depth. Further subtypes included a mine laying Type VIID and a torpedo supply U-boat Type VIIF.

The Type VII U-boat building program began slowly after the Anglo-German Naval Agreement in 1935, by the beginning of the war on 3 September 1939 only eighteen Type VII were in service, but by the end of the war a total of 709 boats had been commissioned. Many more were planned, ordered or even laid down, but the massive building program was abruptly halted in September 1943 when it became clear that this class had become obsolete and construction of U-boats had to focus on the newer elektroboote. At the end of the war, most of the remaining boats were scuttled either by their crews in Operation Regenbogen or later by the British in Operation Deadlight. A few survivors served in foreign navies, the last one was decommissioned in 1970. The lone surviving example, U-995, is on display at the Laboe Naval Memorial located in Laboe, Schleswig-Holstein, Germany.

After the defeat in World War I, the Treaty of Versailles forbade Germany to build submarines. Germany circumvented the treaty by setting up the Dutch dummy company NV Ingenieurskantoor voor Scheepsbouw Den Haag (I.v.S) which continued to design submarines. Based on the World War I design of the Type UB III and its never-built successors Type UF and Type UG, IVS designed the Vetehinen class and in 1931 built three submarines in Finland. Already in 1933 the Reichsmarine wanted to start the construction of a 500 t (490-long-ton) medium attack U-boat, capable of operating in the North Atlantic. Parts were produced, but Hitler held back assembly not wanting to offend Great-Britain with an open breach of the Versailles treaty. The first orders for Type VII U-boats were only given in January 1935, well before Hitler openly renounced the Treaty of Versailles in March 1935. This breach of the Treaty of Versailles was officialized with Great-Britain in the Anglo-German Naval Agreement, where Germany promised to limit the total tonnage of German U-boats to 45% of total tonnage of British submarines.

The Type VII was designed as a single-hull submarine, meaning that the outer hull was also the pressure hull. Although there were saddle tanks, most of the fuel was stored within the pressure hull, which reduced significantly the risk of oil leaks in case of depth-charge attacks. The saddle tanks contained only diving and trimming tanks. The main ballast tank was also located within the pressure hull, and more diving tanks were added outboard in the bow and stern which resulted in a very short diving time of 30 seconds. The deck casing streamlined the pressure hull at the bow and stern.

Type VII submarines were the most widely used U-boats of the war and were the most produced submarine class in history, with 709 commissioned.

All Type VII U-boats were armed with four bow and one stern 53.3 cm (21 in) torpedo tubes. Five torpedoes were carried in the tubes; in the forward torpedo compartment four extra torpedoes were stored below the inner deck and two more were stored in cradles on the inner deck. There was no aft torpedo room; the aft torpedo tube was located in the electrical engine compartment with one reload stored below deck between the two electrical engines. Two extra spare torpedoes were carried externally in a watertight container, one located above the forward torpedo compartment and one behind the conning tower. There were torpedo hatches fore and aft through which torpedoes could be reloaded at harbour, but it was also possible to take on these external spares at sea through these two hatches, by mounting a collapsible trough and a tripod. When during a patrol a spare torpedo was transferred from the external canisters to the inner torpedo room, the torpedo hatch had to be opened and the U-boat was unable to dive in that state. Hence this could only be done in low-risk areas.

At the start of the U-boat building program in 1935, the Germans were only allowed to build a limited number of U-boats and they could not afford to build specialized minelaying U-boats. Instead they developed sea mines that could be laid by any U-boat through the torpedo tubes. A TMA moored mine could be laid in waters with a depth of maximum 270 m (890 ft) and had a length of 3.64 m (11 ft 11 in). Each internal torpedo could be substituted by two SMA mines. The TMB ground mine had a length of 2.31 m (7 ft 7 in) so that for each torpedo, three TMB's could be loaded. In November 1939 a heavier TMC ground mine with a length of 3.39 m (11 ft 1 in) came into service. At the beginning of the war, a Type VII U-boat would typically load eight TMA or twelve TMB in its torpedo tubes on a minelaying mission, and then continue its patrol with the spare torpedoes.

The Type VII mounted an 8.8-centimetre (3.5 in) quick-firing deck gun. This gun was intended for finishing off sinking ships, so that torpedoes could be economized. The gun could also be used in the beginning of the war to give stop sign to ships under the prize law. A U-boat was very vulnerable at the surface and not fit for gun duels as a single hit on the pressure hull could render it unable to dive. From the end of 1942 onwards, the deck gun was removed to save weight for extra anti-aircraft guns.