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A submarine pen (U-Boot-Bunker in German) is a type of submarine base that acts as a bunker to protect submarines from air attack. The term is generally applied to submarine bases constructed during World War II, particularly in Germany and its occupied countries, which were also known as U-boat pens after the phrase U-boat to refer to German submarines.
Keroman U-Boat Base
Keroman Submarine Base was a German U-boat base located in Lorient during World War II. Großadmiral Karl Dönitz decided to build the base on 28 June 1940. Between February 1941 and January 1942 three gigantic reinforced concrete structures were built on the Keroman peninsula. They are called K1, K2 and K3. In 1944 work began on a fourth structure. The base was capable of sheltering thirty submarines under cover. Although Lorient was heavily damaged by Allied bombing raids, this naval base survived through to the end of the war. Lorient was held until May 1945 by the Germans’ Wehrmacht Heer regular army forces, though surrounded by the American Army; the Germans refused to surrender.
Since they could not destroy the base and its submarine pens, the Allies had decided to flatten the city and port of Lorient to cut the supply lines to the U-boat bases. Without resupply of fuel, weapons (e.g. torpedoes), and provisions, it became impossible for those U-boats to return to war patrols in the Atlantic Ocean. Between 14 January 1943 and 17 February 1943, Allied aircraft dropped as many as 500 high-explosive bombs and more than 60,000 incendiary bombs on Lorient; nearly 90% of the city was flattened.
After the war, the base was used by the French Navy until 1997. Rechristened by the French as Base Ingénieur Général Stosskopf in July 1946, the new name commemorated Jacques Stosskopf, a German-speaking Alsatian Frenchman who had been the deputy director of naval construction for the Germans at the base while secretly in the French Resistance, and had given valuable information on submarine movements to the Allies during the war until his activities were discovered and he was killed.
At present, the Keroman U-boat base is open to the public. During tours, the submarine pens of block K3 can be seen. Its roof (3.40 to 7.0 metres (11.15 to 22.97 ft) of steel-reinforced concrete) can be visited, as well as a former anti-aircraft tower on top of the U-boat base. The tower affords an excellent view of the harbour and of the former headquarters of Großadmiral Karl Dönitz of the Kriegsmarine across the bay at Larmor-Plage. The FloreS645, a Daphné-class submarine, launched 1961, can also be visited. Another part of the base has been reconverted for industrial naval activities, with the preparation of racing multihulls.
The Biber (German for beaver) was a German midget submarine of the Second World War. Armed with two externally mounted 21-inch (53 cm) torpedoes or mines, they were intended to attack coastal shipping. They were the smallest submarines in the Kriegsmarine.
The Biber was hastily developed to help meet the threat of an Allied invasion of Europe. This resulted in basic technical flaws that, combined with the inadequate training of their operators, meant they never posed a real threat to Allied shipping, despite 324 submarines being delivered. One of the class’s few successes was the sinking of the cargo ship Alan A. Dale.
A number have survived in museums, including one example that has been restored to operational condition.
The Seehund (German: “seal”), also known as Type XXVII, was a successful series of German midget submarines created during World War II. Designed in 1944, and operated by two-man crews, the submarines were used by the Kriegsmarine during the closing months of the war, sinking nine merchant vessels and damaging an additional three, with 35 losses mostly attributed to bad weather.
The Type I U-boat was the first post–World War I attempt by Nazi Germany’s Kriegsmarine to produce an oceangoing submarine. Only two Type IAs were built, but the decision to halt production on further boats is believed to be because of political decisions and not because of major faults in the Type I design. Although the boats did not have any major design faults, they were known to be difficult to handle due to their poor stability and slow dive rate. The type was based on the design of the Finnish Vetehinen class and the Spanish Type E-1, designed by Ingenieurskantoor voor Scheepsbouw (the company also designed the Soviet S class submarine). The design later served as a basis for the development of other types of boats, primarily the VII and IX classes.
Constructed by Deschimag in Bremen, the first Type IA was launched on 14 February 1936. The two boats produced, U-25 and U-26, were primarily used as training vessels and for propaganda purposes to fly the Nazi flag. In 1940, the boats were called into combat duty due to the shortage of available submarines. Both boats experienced short, but successful combat careers. U-25 participated in five war cruises, sinking eight enemy ships. On 3 August 1940, while on a mine laying mission near Norway, U-25 struck a mine and sank with all hands on board.
U-26 carried out eight war cruises, sinking three merchant ships and damaging one British warship on its first mission laying mines. On its second war cruise, it became the first U-boat during World War II to enter the Mediterranean Sea. U-26 participated in three other successful war patrols, sinking four additional merchant ships. On its eighth war cruise the boat sunk three merchant ships and damaged another ship the next day. The attack on this ship led to severe depth-charging by two British warships, including HMS Gladiolus. Unable to dive, U-26 was forced to surface where she was bombed by a Sunderland flying boat. The crew scuttled the submarine and were rescued by Allied warships.
The Type II U-boat was designed by Nazi Germany as a coastal U-boat, modeled after the CV-707 submarine, which was designed by the Dutch dummy company NV Ingenieurskantoor voor Scheepsbouw den Haag (I.v.S) (set up by Germany after World War I in order to maintain and develop German submarine technology and to circumvent the limitations set by the Treaty of Versailles) and built in 1933 by the Finnish Crichton-Vulcan shipyard in Turku, Finland. It was 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. It appeared in four sub-types.
Type VII U-boats were the most common type of German World War II U-boat. The Type VII was based on earlier German submarine designs going back to the World War I Type UB III and especially the cancelled Type UG, designed through the Dutch dummy company Ingenieurskantoor voor Scheepsbouw den Haag (I.v.S) which was set up by Germany after World War I in order to maintain and develop German submarine technology and to circumvent the limitations set by the Treaty of Versailles, and was built by shipyards around the world. The Finnish Vetehinen class and Spanish Type E-1 also provided some of the basis for the Type VII design. These designs led to the Type VII along with Type I, the latter being built in AG Weser shipyard in Bremen, Germany. The production of Type I was cut down only after two boats; the reasons for this are not certain and range from political decisions to faults of the type. The design of the Type I was further used in the development of the Type VII and Type IX. Type VII submarines were the most widely used U-boats of the war and were the most produced submarine class in history, with 703 built. 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 Type IX U-boat was designed by Nazi Germany’s Kriegsmarine in 1935 and 1936 as a large ocean-going submarine for sustained operations far from the home support facilities. Type IX boats were briefly used for patrols off the eastern United States in an attempt to disrupt the stream of troops and supplies bound for Europe. The extended range came at the cost of longer dive times and decreased maneuverability. It was derived from the Type IA, and appeared in various sub-types.
Type IXs had six torpedo tubes; four at the bow and two at the stern. They carried six reloads internally and had five external torpedo containers (three at the stern and two at the bow) which stored ten additional torpedoes. The total of 22 torpedoes allowed U-boat commanders to follow a convoy and strike night after night. Some of the IXC boats were fitted for mine operations; as mine-layers they could carry 44 TMA or 66 TMB mines.
Secondary armament was provided by one 10.5 cm (4.1 in) deck gun with 180 rounds. Anti-aircraft armament differed throughout the war. They had two periscopes in the tower. Types IXA and IXB had an additional periscope in the control room, which was removed in Type IXC and afterward.
Type X (XB) U-boats were a special type of German U-boat. Although intended as long-range mine-layers, they were later used as long-range cargo transports, a task they shared with the Type IXD and Italian Romolo-class submarines.
Type XIV – Milk Cow
The Type XIV U-boat was a modification of the Type IXD, designed to resupply other U-boats, being the only Submarine tenders built which were not surface ships. They were nicknamed Milchkuh/Milchkühe (plural)(milk cows). Due to its large size, the Type XIV could resupply other boats with 613 t (603 long tons) of fuel, 13 t (13 long tons) of motor oil, four torpedoes, and fresh food that was preserved in refrigerator units. In addition, the boats were equipped with bakeries, in order to provide the luxury of fresh bread for crews being resupplied. They had no torpedo tubes or deck guns, only anti-aircraft guns.
In 1942, the milk cows allowed the smaller Type VIIC boats to raid the American coast during the “Second Happy Time” of the Battle of the Atlantic. The milk cows were priority targets for Allied forces, as sinking one milk cow would effectively curtail the operations of several regular U-boats and force them to return home for supplies. Ultra intercepts provided information concerning sailing and routing, and this, coupled with improved Allied radar and air coverage in the North Atlantic, eliminated most of them during 1943. By the end of the war, all ten had been sunk. Milk cow duty was especially hazardous; 289 sailors were killed out of an estimated complement of 530–576 men.
The Type XVII U-boats were small coastal submarines that used Hellmuth Walter’s high-test peroxide propulsion system, which offered a combination of air-independent propulsion and high submerged speeds.
Type XXI U-boats, also known as “Elektroboote” (German: “electric boat”), were a class of German diesel-electric submarines designed during the Second World War. The submarines were rushed into production prematurely, and all of those built suffered from significant defects. As a result, only four of the submarines were completed during the war, and only two went on combat patrol with no action taken.
They were the first submarines designed to operate primarily submerged, rather than spending most of their time as surface ships that could submerge for brief periods as a means to escape detection or launch an attack. They incorporated a very large number of batteries to improve the time they could spend underwater, up to several days, and only surfaced to periscope depth for recharging via a Schnorchel. The design included a huge number of general improvements as well; much higher underwater speed through an improved hull design, greatly improved diving times, power assisted torpedo reloading, and greatly improved crew accommodations.
The design proved enormously influential in the post-war era. Several navies took XXIs on their lists and operated them for decades in various roles, and almost every navy introduced new submarine designs based on them. These include the Soviet Whisky , US Tang and the UK Porpoise, all of which were based on the XXI design to one degree or another. The basic design remains the basis for modern diesel-electric submarines to this day.
German Type XXIII submarines were the first so-called elektroboats to become operational. They were small coastal submarines designed to operate in the shallow waters of the North Sea, Black Sea and the Mediterranean Sea, where larger Type XXI Elektro boats were at risk in World War II. They were so small they could carry only two torpedoes, which had to be loaded externally. As with their far larger sisters—the Type XXI—they were able to remain submerged almost all of the time and were faster than conventional U-boats, due to the improved streamlining of their shape, batteries with larger capacity and the snorkel, which allowed the diesel engines to be used while submerged. The Type XXI and XXIII U-boats revolutionized post-war submarine design. Nearly a thousand Type XXIII boats were projected towards the close of World War II, but most of these were either canceled, scrapped incomplete or only projected.
Uncompleted U-boat Projects
During World War II, Germany’s Kriegsmarine considered various submarine designs for specialized operations or improving U-boat performance. Many of these designs did not come to fruition for various reasons. Some were abandoned due to practical considerations. Others towards the end had to be abandoned, as the yards were overrun by allied forces.
- The Type III U-boat was a 1934 project for a purpose-built minelayer based on the Type IA U-boat. The Type III U-Boat would have been similar to the Type IA, but with a hull lengthened by 7.5 m, and a total displacement of 970 tons. The Type III U-Boat was planned to carry an armament of 54 to 75 mines (depending on the type carried), two 105-mm deck guns, and one 20-mm antiaircraft gun.
- The Type IIIA U-boat was a planned minelayer similar to the Type IA U-boat. It would have had a larger outer hull than the Type IA, and featured a large, watertight cylindrical hangar on the aft deck, which would have carried two small motor torpedo boats. The boat would have carried 48 mines, and used the smaller boats to help lay and recover mines. The project was dropped as impractical.
- The Type IV U-boat was a planned resupply and repair U-boat, intended to meet other U-boats at sea and resupply them with torpedoes, fuel, food/water, and spare parts, and also be capable of performing light repair work.
- The Type V U-boat was an experimental midget submarine designed by Hellmuth Walter using his hydrogen peroxide-fuelled turbine. Only one vessel, the V-80, was built.
- The Type VI U-boat was a planned conversion of Type IA U-boats to run both submerged and surfaced from steam propulsion.
- The Type VIIE U-boat was planned to make use of a lightweight engine, and with the saved weight, increase the thickness of the pressure hull – thus allowing for greater diving depths. The project was canceled.
- The Type VIII U-boat has very little information is available, other than it was planned for production in the event of mobilization in 1935.
- The Type XI U-boat was planned as an artillery boat; its main armament would have been four 128-mm guns, in two twin gun turrets. It would have also carried an Arado Ar 231 collapsible floatplane. Four boats (U-112, U-113, U-114, and U-115) were laid down in 1939 but canceled at the outbreak of World War II. Had the Type XI U-boat been constructed, it would have had a completely new hull design and a submerged displacement of 4,650 tons – she would have been by far the largest of the U-boats and the second-largest diesel submarine after the Japanese I-400-class submarine. Its purpose was to engage ships including escorts in artillery duels at relatively long range, then dive away if they came within a certain threshold distance. Many anti-submarine escorts of WW2 including the Flower corvettes would have been too small and too poorly equipped with forwarding guns to cope with this approach.
- The Type XII fleet U-boat was a design from 1938. It had eight torpedo tubes, six at the bow and two at the stern, and was to carry 20 torpedoes. The gun armament was to be the same as for the type IX boats. Designed size equal to the later, larger type IX version IXD model, but with even more powerful engines and motors planned, allowing faster speeds both above and below the surface. No contracts were granted for these boats.
- The Type XIII U-boats was a further development of type II coastal U-boat, with four torpedo tubes and one 20-mm antiaircraft gun. No contracts were granted for these boats.
- The Type XV and XVI U-boats were intended for very large transport and repair boats (5,000-tons and 3,000-tons, respectively) intended to carry torpedoes, food, and oil as cargo. The engine layout was to be the same as for the VIIC. No contracts were granted for these boats.
- The Type XVIII U-boat was a project for an attack boat using the Walter propulsion system. Two boats (U-796 and U-797) were laid down in 1943, but construction was canceled in March 1944.
- Type XIX was a project for an unarmed transport U-boat, based on the Type XB minelayer.
- Type XX was another project for a transport U-boat based on the Type XB; it would have had a shorter hull than the Type XB, but had a greater beam and draft. Thirty Type XX U-boats were laid down in 1943, but construction stopped in 1944. In August 1944, construction on three Type XX U-boats (U-1701, U-1702, and 1703) resumed but again stopped in early 1945.
- The Type XXII U-boat was intended for coastal and Mediterranean use. They used the Walter propulsion system and would have had a crew of two officers and 10 men. They were to have three torpedo tubes, two at the bow (below the CWL) and one aft of the bridge (above the CWL). Initially, 72 contracts were awarded to Howaldtswerke (36 to the yard in Hamburg and 36 in Kiel), but of those, only two had been laid down and had received U-boat numbers (U-1153 and U-1154) before they were all canceled in late 1943.
- The Type XXIV was a 1943 design for an ocean-going U-boat using the Walter system. It was to have 14 torpedo tubes, six at the bow, and four each side aft.
- The Type XXV U-boats were intended to be electric propulsion-only boats for coastal use. The design was 160 tons with a crew of about 58 men and would have had two torpedo tubes fitted at the bow.
- The Type XXVI was a high-seas U-boat propelled by the Walter system. They would have had a crew of three officers and 30 men, with ten torpedo tubes, four at the bow and six in a so-called Schnee organ, and no deck guns; 100 contracts were initially awarded to the Blohm & Voss yard in Hamburg (U-4501 through U-4600) and sections were under construction for U-4501 through U-4504 when the war ended. The other contracts had been canceled.