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Type VII submarine
German submarine class of World War II From Wikipedia, the free encyclopedia
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Type VII U-boats were the most common type of German World War II U-boat. 704 boats were built by the end of the war.[ambiguous] The type had several modifications. The Type VII was the most numerous U-boat type to be involved in the Battle of the Atlantic.
The lone surviving example, U-995, is on display at the Laboe Naval Memorial located in Laboe, Schleswig-Holstein, Germany.
At the start of the Second World War the Type VII class was – together with the British U, S and T class and Dutch O 21 class – one of the most advanced submarine classes in service.[4]
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Design
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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 submarine 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 Versailles treaty in March 1935.[5] This breach of the Versailles treaty 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.[6]
Type VII submarines were the most widely used U-boats of the war and were the most produced submarine class in history, with 704 built.[7][8]
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Armament
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All Type VII U-boats were armed with four bow and one stern 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 either suspended by chains or stored in cradles sideways. 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. An extra spare torpedo was carried externally in a watertight container. 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 taking on spares, the U-boat was very vulnerable and this could therefore only be done in low-risk areas.[9]
The Type VII mounted a 8.8-centimetre (3.5 in) quick-firing deck gun.[10] 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 unfit to dive. From the end of 1942 onwards, the deck gun was removed to save weight for extra anti-aircraft guns.[11]
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Subclasses
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Type VIIA[a]
Ten Type VIIA boats were built between 1935 and 1937 in two batches: six at Deschimag AG Weser in Bremen and four at Friedrich Krupp Germaniawerft, Kiel. Six were lost in action, two were lost in accidents in the Baltic sea and the remaining two were scuttled on 4 May 1945.[13]
The boat was powered on the surface by two MAN AG, 6-cylinder, 4-stroke M6V40/46 diesel engines, giving a total of 2,300 brake horsepower (1,700 kW). When submerged it was propelled by two Brown, Boveri & Cie (BBC) GG UB 720/8 double-acting electric motors, giving a total of 750 horsepower (560 kW).[13]
Type VIIB
After evaluating and comparing the commisioned Type I and Type VII U-boats, the Kriegsmarine asked for an improved version of the Type VII which would be named Type VIIB. Four requirements were formulated: a smaller turning circle, better surface speed, larger range and more torpedoes. Manoeuvrability was improved by installing one rudder in line with each of the two propellers so that the wash of the propellor had much more effect on the rudder. This change fitted well with another requirement of improved armament and reserve torpedo capacity. The external stern torpedo tube could now be mounted within the pressure hull, between the two rudders. The internal tube allowed for reloading and for firing on the surface. One spare torpedo for the stern tube was carried internally and two more spare torpedoes, one below the forward deck and one below the afterdeck, were stored externally in pressure-tight containers.[14][12]
To improve the range, the hull was extended by 2 m (6 ft 7 in) to increase the internal fuel storage, and saddle tanks with 40,000 L (1,400 cu ft) of fuel added 2,500 nautical miles (4,600 km; 2,900 mi) of range at 10 knots (19 km/h; 12 mph). With the installation of saddle tanks, the advantage of having all fuel stored internally within the pressure hull, and hence avoiding the risk of oil leaks when the outer skin was damaged, was lost.[14]
Two types of diesel engines were installed in the Type VIIB : the first one was the same MAN M6V40/46 used in the Type VIIA, the second one was the near identical Germaniawerft F46. Power output of these engines was increased by installing superchargers. On the MAN engine the compressor of the supercharger was driven by exhaust gasses and power increased to 2,800 brake horsepower (2,100 kW). The Germaniawerft diesel had a compressor driven by the shaft of the engine itself, and delivered 3,200 brake horsepower (2,400 kW) in total.[15][16] MAN powered U-boats reached a top speed of 17.2 knots (31.9 km/h; 19.8 mph), with Germaniawerft diesels top speed was 17.9 knots (33.2 km/h; 20.6 mph).[16][12]
All these changes increased the surface displacement of the Type VIIB with 120 t (120 long tons), but standard displacement rose only from 500 t (490 long tons) to 517 t (509 long tons).[14][12]
Some of the Type VIIB had the same Brown, Boveri & Cie GG UB 720/8 electric motors, others had the AEG GU 460/8-276, which was identical to the former.[12][15]
The first seven Type VIIB were ordered on 21 November 1936 from Germaniawerft, followed by two more on 15 May 1937 and again two more on 16 July 1937.[17] After the revision of the Anglo-German Naval Agreement, further orders for four Type VIIB were given to Germaniawerft, Bremer Vulkan and Flender Werke each.[18] Flender Werke also built a fifth Type VIIB U-83 under an export contract but the boat was taken over on 8 August 1938.[19] It lacked a stern tube.[12][20][19] A total of twenty-four Type VIIB entered service between 1938 and 1941: twenty were lost at sea and the remaining four were scuttled at the end of the war.[16]
Type VIIC
The Type VIIB was a very satisfactory design, but when a sonar needed to be installed, extra room had to be created by adding a full frame section of 0.6 m (2 ft 0 in) in the control room, resulting in the Type VIIC. The extra weight reduced speed marginally, and the extra space in the saddle tanks was not used for fuel but for an extra buoyancy tank. One of the electrical air compressors was replaced by a Junkers diesel-powered air compressor in order to reduce the demands on the electrical systems of the U-boat.[21]
They had the same torpedo tube arrangement as their predecessors, except for U-72, U-78, U-80, U-554, and U-555, which had only two bow tubes, and for U-203, U-331, U-351, U-401, U-431, and U-651, which had no stern tube.[22]
A few of the early Type VIIC U-boats were equipped with the 2,800 bhp (2,100 kW) MAN M6V40/46, which gave a top speed of 17 kn (31 km/h; 20 mph), others had the 3,200 bhp (2,400 kW) Germaniawerft F46 which gave a top speed of 17.7 kn (32.8 km/h; 20.4 mph).[23][24]
For submerged propulsion, electric motors were produced by four enterprises to the same design, and they had identical performance : the AEG GU 460/8-276 and BBC GG UB 720/8 which were already installed in previous types, and the Garbe, Lahmeyer & Co. RP 137/c or Siemens-Schuckert-Werke (SSW) GU 343/38-8.[25]
The first VIIC boat U-93 was commissioned on 30 July 1940.[26]
Type VIIC/41
In 1941 it was examined how U-boats could be improved. A first requirement for higher surface speed could not be met without large modifications to the design. A new design would disrupt current production of U-boats too much, so it was investigated how the diving depth could be increased. By saving 11.5 t (11.3 long tons) weight on simpler diesel and electric engine installations, the weight of the hull could be augmented with 10 t (9.8 long tons) By increasing the thickness of the hull from 18.5 mm (0.73 in) to 21 mm (0.83 in) mm, diving depth increased by 20%. This improved design was called Type VIIC/41; the first were ordered in October 1941, and delivered in August 1943.[27] A total of 87 were delivered.[28] All of them from U-1271 onwards lacked the fittings to handle mines.[23]
The only preserved Type VII U-boat is the VIIC/41U-995 that is on display at the Laboe Naval Memorial.[29]
Type VIIC/42
The greatest danger for a submerged U-boat was to be detected by Sonar. By coating the outer hull of a U-boat with rubber anechoic tiles, it was hoped that the acoustic waves of the sonar would be absorbed rather than reflected. During 1941, tests with the rubber coating were conducted with U-67, but these tests were disappointing and the project was abandoned. The only solution left was to increase once more the diving depth by using thicker steel for the pressure hull. The steel rolling equipment at the builders yard limited the maximum thickness to 28 mm (1.1 in). The weight of the hull increased from 68.3 t (67.2 long tons) to 154.3 t (151.9 long tons) needing an increase from 4.7 m (15 ft 5 in) to 5 m (16 ft 5 in) in beam, in order to create more buoyancy. The saddle tanks were also enlargened so that range increased to 12,600 nautical miles (23,300 km; 14,500 mi). The maximum speed of 17 knots (31 km/h; 20 mph) of a Type VIIC proved to be unsufficient for keeping in touch with the enemy during convoy battles and an increase in top speed was also required. The same diesel engines were used, but the hull was lengthened by 0.8 metres (2 ft 7 in) to provide space for superchargers for the diesels. With the additional power, it was hoped speed would increase to 18.6 knots (34.4 km/h; 21.4 mph).[30]
Even before the design was finalized on 10 November 1942, a preliminary order of 12 boats had already been placed. By 17 April 1943 174 boats had been ordered from twelve shipbuilding yards, but due to problems with producing the new steel alloy for the reinforced pressure hull, construction was slow to start. Assembly at the yards had not yet started when all orders were cancelled on 24 July 1943 in favor of the new Type XXI.[31]
Type VIIC/43
Early in 1943 it became obvious that operations during convoy battles demanded a better armament with a higher number of ready-to-fire torpedo tubes rather than fewer torpedo tubes with more reloads. During convoy battles an attacking U-boat rarely got the occasion to withdraw to reload and attack again. Therefore a new design VIIC/43 was made based on the Type VIIC/42 but with six bow torpedo tubes and two at the stern. But as the new deep-diving U-boats were urgently needed at the front, it was decided on 11 May 1943 to cancel this project as it would delay production of the Type VIIC/41 and VIIC/42.[32]
Type VIID
At the beginning of World War II, there were four large Type XB minelayers under construction, intended for laying anchored SMA mines in distant waters. Any type of U-boat could lay TMB ground mines through torpedo tubes but still there was a need for a medium sized U-boat able to lay SMA mines on British and French coasts. In order to fill this gap, the Type VIIC was developed into a Type VIID SMA minelayer by simply adding a 9.8 m (32 ft 2 in) section with five mineshafts between the control room and the crew compartment of the petty officers. As the saddle tanks also covered the extra section, the fuel storage and range increased considerably. Six boats were ordered on 16 February 1940, and the first was laid down on 1 October 1940.[33] The six Type VIID U-boats were in service in early 1942, but the SMA mine had not yet been cleared for front usage. As the Type VIID had kept the same offensive capacities as their TypeVIIC sisterships, they were used for regular combat patrols, where they could benefit from their extra range.[34]
Type VIIE
The Type VIIE was a project for trying out new lightweight V12 two-stroke diesel engines in a Type VIIC. The idea was again to try to save weight so that extra weight could go to the presurre hull. This project remained a design as this new engine was delayed and finally abandoned before any construction had started.[35][36]
Type VIIF
Up to mid-1941 it had been possible to provide U-boats with spare torpedoes through surface supply ships at remote locations. But after the sinking of the German battleship Bismarck in May 1941 all supply ships were hunted down. Towards the end of 1941 attempts to resupply from the German auxiliary cruiser Atlantis ended in disaster when both the auxiliary cruiser and its supply ship Python were sunk by a British cruiser. The Type XIV supply boats were intended for fuel resupply and carried only four spare torpedoes. The large Type XB minelayer was also scheduled to be used as a supply boat but could carry only nine spares. Designing a whole new large torpedo transporter would eat away much resources both from the planning department and the shipbuilding yards, so the simplest and best idea was add an extra compartment to a Type VIIC, just like had been done before for the Type VIID minelayer.[37] The extra compartment measured 10.5 m (34 ft 5 in) and had an extra torpedo hatch to load twenty[b] torpedoes, which were stored in four banks.[40]
The Type VIIF had the same engines as the Type VIIC, but was with 1,084 t (1,067 long tons) much heavier. With a more streamlined hull than the Type VIID, she did not loose much speed however. Just like with the Type VIID, the saddle tanks ran along the extra compartment and provided extra fuel and range up to 14,700 nmi (27,200 km; 16,900 mi).[40]
On 22 August 1941 four Type VIIF were ordered, with expected delivery beginning of 1943.[37] When these four boats entered service in early 1943, it was no longer realistic to use them in their intended role as Allied air power made supply missions in the battle zones too dangerous. Instead the boats were used to supply remote bases in Norway, and two were sent to resupply the Monsun Gruppe in Penang, Malaysia.[40]
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In foreign service
- On 27 Augustus 1941 Aircraft surprised U-570 on the surface south of Iceland. Damaged by depth-charges the U-boat was unable to escape further attack and surrendered. British ships took the U-boat in tow to Iceland where she was beached. U-570 was repaired and entered service as HMS Graph with the Royal Navy on 31 October 1941.[41]
- On 1 May 1942 U-573 was heavily damaged by aircraft East of Gibraltar. She limped into the neutral Spanish port of Cartagena, Spain. She was allowed three months for repairs by the Spanish authorities but the U-boat could not be repaired in time and was finally sold to Spain where she entered service as S01.[42]
- U-471 was destroyed in the military port of Toulon by an air raid,[43] but was repaired in 1945 and served untill 1963 in the French Navy as Millé.[44]
- U-766 was decommisioned on 20 August 1944, and disabled on 15 September 1944 in the port of La Pallice when the port fell to Allied forces. She was declared a war prize, repaired and recommisioned in the French Navy as Laubie.[45]
- Three U-boats which surrendered to the Allies in May 1945 were transferred to the Royal Norwegian Navy : U-926, U-995 and U-1202 entered service as Kya, Kaura and Kinn respectively.[46]
- U-1057, U-1058, U-1064, U-1305' surrendered at the end of the war, and were allocated as war prizes to the Soviet Navy,[47] they were renamed S-81, S-82, S-83 and S-48 respectively.[46]
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Specifications
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Footnotes
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