Type VII submarine
The Type VII was a class of medium 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 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 strengthened 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,, is on display at the Laboe Naval Memorial located in Laboe, Schleswig-Holstein, Germany.
Design
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 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 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 built U-boats of the war and were the most produced submarine class in history, with 709 commissioned.
Armament
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 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 and had a length of. Each internal torpedo could be substituted by two TMA mines. The TMB ground mine had a length of so that for each torpedo, three TMB's could be loaded. In November 1939 a heavier TMC ground mine with a length of 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 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.
As a defense against aircraft, Type VII U-boats received one C/30 anti-aircraft gun which was mounted on a platform at the back of the conning tower. By mid-1942 Allied aircraft attacks had become so frequent that an upgrade was needed. The platform was enlarged so that more guns could be mounted and a second platform was added behind and below the first one. A more powerful gun was needed but was not readily available. As a stopgap solution, the 2 cm C/30 was replaced with the improved 2 cm C/38 gun. This gun was more reliable and had a slightly increased rate of fire. The intention was to install two twin C/38 mountings on the higher platform and one quadruple C/38 mounting on the lower platform, but if sufficient twin or quadruple mountings were not available, single C/38 were installed instead. The first single C/38s were installed in mid-January 1943 and the first quad C/38 mounting in March. The first twin C/38 mountings became available on 15 June and were standard by October. On 30 June 1943 U-boats were ordered to delay their sailings until they had received an anti-aircraft gun upgrade. The 2 cm C/38 gun proved to be too weak, a heavier gun was needed but the existing 3.7 cm SK C/30 was not adequate for its slow rate of fire. A naval version of the 3.7 cm Flak 43 was developped as a substitute and was ready for standard installation by November 1943. The new 3.7 cm gun replaced the quadruple 2 cm on the lower platform. There were some experiments with other anti-aircraft gun configurations, but these were not continued as with the arrival of the snorkel, U-boats could avoid aircraft by cruising submerged so the urgence for improved anti-aircraft guns diminished.
Subclasses
Type VIIA
A Type VIIA U-boat had an overall length of, a beam of and a draft of. On the surface a Type VIIA displaced, and submerged. The length of the pressure hull was and had a maximum diameter of. Type VIIA U-boats had an externally mounted aft torpedo tube which could not be reloaded; they did not have a spare aft torpedo nor external canisters to store spare torpedoes.The boat was powered on the surface by two MAN AG, six-cylinder, four-stroke M6V40/46 diesel engines, giving a total of, which gave a maximum speed of. With a fuel capacity of, the range was at. When submerged it was propelled by two double-acting electric motors, giving a total of. Maximum submerged speed was and maximum range was at.
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. The first Type VIIA was laid down on 11 November 1935, launched on 24 June 1936 and commissioned on 12 August 1936. Six were lost in action, two were lost in accidents in the Baltic sea and the remaining two were scuttled on 4 May 1945.
Type VIIB
After evaluating and comparing the commissioned Type I and Type VII U-boats, the 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 propeller 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.To improve the range, the hull was extended by to increase the internal fuel storage, and saddle tanks with of fuel added of range at. With the installation of fuel tanks in the 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.
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. The Germaniawerft diesel had a compressor driven by the shaft of the engine itself, and delivered in total. MAN powered U-boats reached a top speed of, with Germaniawerft diesels top speed was.
All these changes increased the surface displacement of the Type VIIB with, but standard displacement rose only from to. The first seven Type VIIB were ordered on 21 November 1936 from, followed by two more on 15 May 1937 and again two more on 16 July 1937. After the revision of the Anglo-German Naval Agreement, further orders for four Type VIIB were given to, and each. also built a fifth Type VIIB under an export contract but the boat was taken over on 8 August 1938. It lacked a stern tube. At the beginning of World War II, only eight Type VIIB were commissioned, 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.