Type XXI submarine

Until 1943, The German Navy intended to equip the new generation of U-boats with a revolutionary underwater propulsion system, the Walter-turbine. This turbine provided high underwater speeds and new streamlined U-boat hulls were designed for these U-boats. Two types of 'Walter' U-boats were developed: an ocean-going Type XVIII and a coastal Type XVII. Germany lacked the resources to produce the hydrogen peroxide fuel needed for these turbines, and these turbines consumed far more fuel than a U-boat could store in her tanks. As these problems were gradually understood, in March 1943, German engineers took up the idea of using the large turbine room and hydrogen peroxide tanks of these Type XVII and Type XVIII U-boats for larger electrical engines and extra battery cells. On 19 June 1943, the German navy ordered these ideas to be worked out as a new Type XXI submarine, which was to replace the Type IX submarine. Using the Type XVIII design for the hull, armament, and control systems, and the new supercharged diesel engine intended for the Type VIIC/42 submarine, the Type XXI was underpowered and slower on the surface than its predecessors the Type VII and Type IX, but low surface speed was not considered a problem. With its superior submerged speed and endurance, a Type XXI could position itself undetected for a convoy attack, and with a new quick-loading device, it could fire eighteen torpedoes in twenty minutes. Already on 29 June, Karl Dönitz, the head of the German navy, approved the Type XXI as the successor for both the long-range Type IX, and Type VII for operations against the North-Atlantic convoys. The main features of the Type XXI were the hydrodynamically streamlined hull and conning tower and the large number of battery cells, roughly triple that of the Type VII. This gave these boats great underwater range and dramatically reduced the time spent on or near the surface. They could travel submerged at about for about 75 hours before recharging batteries, which took less than five hours using the snorkel due to the new supercharged diesel engines. Being designed primarily for submerged use, the Type XXI's maximum surface speed was lower than that of the Type IX (18.2 knots) but its submerged speed was more than twice that of the Type IX (17.2 knots versus 7.7 knots), because they were equipped with much more powerful electric drive motors and had less drag. The Type XXI was also much quieter than the VIIC, making it more difficult to detect when submerged, and the design eliminated protruding components that had created drag in earlier models. The ability to outrun many surface ships while submerged, combined with improved dive times (also a product of the new hull form), made the Type XXI much more difficult to pursue and destroy. It could sprint when positioning for an attack, while older boats had to surface to sprint into position. This often revealed a boat's location, especially after aircraft became available for convoy escort. The Type XXI was also equipped with a pair of electric "creep motors" for silent running. In addition, the Type XXIs had better facilities than previous U-boat classes, with much roomier crew berths, and a freezer to prevent food spoilage. ==Characteristics==

Type XXIs had an overall length of The boats' beam was , the draught was , with a height of . The pressure hull had a length of and had a width of . The boats displaced when surfaced and when submerged. The complement consisted of five officers and fifty-two enlisted men. Constructional, test and crush diving depth were , and respectively. Propulsion As the emphasis was laid on enhanced submerged performance, Siemens-Schuckert designed new GU265/30 double-acting electric motors which were more powerful than the diesel engines. Two of these large electrical motors were installed in the original walter-turbine compartment, together with two small GW323/28 electrical motors for slow silent running. The Type XXI had two MAN six-cylinder four-stroke M6V40/46KBB diesel engines with a total of for use on the surface and two double-acting electric motors with a total of for underwater use. These engines powered two shafts, which gave the boats a top surface speed of and when submerged. Cruising range was at on the surface and at submerged. Armament The Type XXI was the first U-boat to be equipped with six bow torpedo tubes, but had no stern torpedo tube. Six torpedoes were carried within the tubes and another seventeen could be stored in racks immediately behind the tubes. Reloading was done by hoisting a torpedo on a rail hanging from the upper pressure hull. An electrically powered trolley could push the torpedo much into the torpedo tube much faster than had been possible in manual reloading. A full second salvo of six torpedoes was possible five to six minutes after the first salvo, and a third salvo could be fired within twenty minutes. It was intended to make it possible to substitute twelve mines for four torpedoes. Four torpedo tubes could contain three mines each and eject these mines with compressed air. But no Type XXI was ever equipped with the needed minelaying gear. The anti-aircraft armament consisted of two twin 2 cm C/38 guns, mounted in two turrets on the enclosed bridge. The design of this enclosed bridge and anti-aircraft turrets came from the Type XVII. As designed, these turrets were equipped with twin 3 cm M44 guns, but the development of these new guns was delayed and instead the well-proven but obsolete 2 cm C/38 was installed. Sensors Just like all other U-boat types, the Type XXI was equipped with a passive sound listening device, the Gruppenhorchgerät, often abbreviated to GHG. Until 1943 the sensors of the GHG in a U-boat were mounted as far as possible below the waterline towards the bow, with the receiver membranes fitted into the hull plating. In order to give the GHG a better performance, and to allow the GHG to be used at higher submerged speeds, the sensors for the Type XXI were mounted in a 'balcony', a round construction protruding from the keel at the bows. The receivers were arranged in two horizontal 'horseshoe' lines, which allowed even accurate sound location in all directions except the sector right aft. This arrangement allowed the GHG to be used effectively both surfaced and submerged at all depths. The increased submerged speed of the Type XXI necessitated the installation of the receivers behind steel plates. The range of the GHG depended much on the size and speed of the target, but a ship moving at 10 knots could be detected at a range of minimum with an accuracy of 1 degree. The GHG could not give bearings and distance to target accurate enough for torpedo firing control. As it was intended that the Type XXI attack submerged without the use of periscopes, an active sonar called 'S-gerät' was installed for this purpose. The S-gerät has a radius of . Because the sound pulses of the S-Gerät could give away the presence of a U-boat, target acquisition was done with the GHG and the S-gerät was only activated when the attack started. The Type XXI boats were fitted with the FuMO 65 Hohentwiel U1 with the Type F432 D2 radar transmitter. It was intended to install a FuMO 84 Berlin II and FuMO 391 Lessing as from the summer of 1945. The FuMo 84 was a retractable, tactical radar with a wavelength of 9 cm, which could be operated at periscope depth, whilst the FuMO 391 was an air search radar operating at a wavelength of 2.4m. ==Construction==

Section building On 6 July 1943 the first orders for 102 Type XXI were placed at six yards, with expected delivery of three prototypes in November 1944 and expected start of series production by March 1945. These U-boats would not be ready for operational use before 1946. Since new U-boats were instrumental in trying to regain the initiative in the Battle of the Atlantic, Karl Dönitz the commander of the German Navy asked Albert Speer, the Minister of Armaments to find a way to speed up construction. was appointed by Speer as head of the Committee of Ship Construction and with his experience in the automobile industry, he introduced the concept of prefabricated section assembly in U-boat building. Merker expected that with this new building method, the first delivery of a Type XXI could be put forward to April 1944, with series production of thirty U-boats a month starting in August 1944. The hull of the Type XXI was split into eight sections, the conning tower superstructure was added as a ninth section. Construction and assembly of these sections was executed in three steps: first crude sections were constructed at steel factory sites scattered all over Germany. These crude sections were then transported to section yards where equipment was installed. Finally these sections were assembled at ship yards. Three ship yards were selected for assembly: Blohm & Voss of Hamburg, AG Weser of Bremen and Schichau-Werke of Danzig. This new method allowed for a hypothetical construction time of less than six months per vessel. In practice all the assembled U-boats were plagued with severe quality problems that required extensive post-production work and time to rectify. One of the reasons for these shortcomings was that crude sections were made by companies having little experience with shipbuilding. Building program The first orders were placed on 6 November 1943, envisaging a monthly assembly of twelve U-boats at Bremen, thirteen at Hamburg and eight at Danzig. Between August and December 1944, the assembly at Bremen would gradually shift from the AG Weser to the Bremer Vulkan yard in the Valentin submarine pens, a massive, bomb–proof concrete bunker. The pens were constructed between 1943 and 1945, using more than 12,000 foreign forced labourors, concentration camp prisoners and prisoners of war, of which more than 4,000 died because of malnutrition, exhaustion and maltreatment. The building program suffered from the onset with problems: the Strategic bombing disrupted the production of crude sections, diesel engines and electrical motors. Crude sections were produced at the steel yards with too much tolerance on the diameter of the pressure hull resulting in extra adjustment work at the section yards. On 10 March 1944 it was acknowledged that no more than sixty-three U-boats could be delivered by August 1944. Further problems were discovered during or after assembly: many electrical systems had been replaced with a hydraulic equivalent but experience was lacking for installing these advanced hydraulics. The diesel supercharger proved useless for submerged snorkel propulsion, so as surface propulsion was only of secondary importance, the superchargers were abandoned in the end, but this left the boat with far less diesel power. The Naval Construction program of 1 June 1944 included the building of 580 Type XXI, with 155 built in 1944 and a monthly production of twenty-two units in 1945. Shortages in skilled labor at the yards and problems with sections arriving incomplete at the assembly yards, led to the revised construction program of 7 September which reduced the number of Type XXI to be built in 1944 to 120. Allied air attacks continued to disrupt the industrial production and transport of materials to the yards. From September 1944, the Allied advance from Paris to the Rhine threatened the Ruhr industrial area, which caused a sharp decline in steel deliveries to the construction yards. As a consequence the building program had to revised and downscaled every few weeks. Speer nor Merkel were able to mitigate any of these problems, and resorted to force and threats in order to keep the building program on track. On 1 October 1944 the yard director of Bremen Deschimag was arrested and imprisoned for criticizing the section building method and the unrealistic production goals. Finally in February 1945 Merkel decided to cancel most of the Type XXI orders and to focus on assembling the already produced sections. In March the yard in Danzig was evacuated before the Russian advance. At Bremen, daily Mosquito precision bombardments brought the construction at the Deschimag yard to a virtual standstill, and the transfer of the U-boat assembly to the Valentin shelter was thwarted by the destruction of these bunkers with Grand Slam "earthquake" bombs. == Evaluation ==

A post-war assessment of the Type XXI by the United States Navy concluded that while the design had some admirable features, it was seriously flawed. The engines were underpowered, which limited the surface speed and increased the time required to charge the batteries. The hydraulic system was unduly complex, and its main elements were located outside the pressure hull. This made the system highly vulnerable to corrosion and damage. The snorkel was also badly designed, and difficult to use in practice. The submarines had poor structural integrity due to the manufacturing problems. This rendered the submarines highly vulnerable to depth charges, and gave them a lesser maximum diving depth than earlier U-boat designs. Due to the combination of design and construction problems, journalist Clay Blair judged that "the XXI could not have made a big difference in the Battle of the Atlantic. ==Wartime and post-war service==

Germany moored at Bergen, Norway (May 1945). The Type XXI in the middle is U-2511 Towards April 1945, some Type XXIs sailed from Germany to Norway as ports were evacuated before advancing Allied armies arrived. Only sailed from Norway for a war patrol. After an abortive attempt on 18 April, she sailed on 3 May. When on 4 May she received the order to cease hostilities U-2511 returned to Norway. On her return voyage, U-2511 came across the heavy cruiser , made a practise attack but withheld fire. During 1957, , which had been scuttled at the end of the war, was raised and refitted as research vessel Wilhelm Bauer of the Bundesmarine. It was operated by both military and civilian crews for research purposes until 1982. During 1984, it was made available for display to the public by the Deutsches Schiffahrtsmuseum (German Maritime Museum) in Bremerhaven, Germany. France surrendered to the British, but the U-boat was allocated to the French. She was towed in January 1946 to Cherbourg and commissioned on 9 April 1951 in the French Navy as Roland Morillot. The submarine was used for active service during the Suez Crisis in 1956. She remained in commission until 1967 and was scrapped in 1969. Soviet Union Four Type XXI boats were assigned to the USSR by the Potsdam Agreement; these were , , , and , which were commissioned into the Soviet Navy as , , B-29, and (later B-100) respectively. However, Western intelligence believed the Soviets had acquired several more Type XXI boats; a review by the US Joint Intelligence Committee for the Joint Chiefs of Staff during January 1948 estimated the Soviet Navy then had 15 Type XXIs operational, could complete construction of 6 more within 2 months, and could build another 39 within a year and a half from prefabricated sections, since several factories producing Type XXI components and the assembly yard at Danzig had been captured by the Soviets at the end of World War II. U-3538 — U-3557 (respectively TS-5 – TS-19 and TS-32 – TS-38) remained incomplete at Danzig and were scrapped or sunk during 1947. The four boats assigned by Potsdam were used in trials and tests until 1955, then scuttled or used for weapon testing between 1958 and 1973. United Kingdom , Kittery, Maine After the German surrender on 8 May 1945, the British captured five Type XXI in Norway, and renamed them: U-3515, U-2529, U-3035, U-3041 and became respectively N-27, N-28, N-29, N-30 and N-41. The first four were transferred to the Soviet Navy in February 1946, N-41 was used for tests until scrapped in November 1949 at Newport. United States The United States Navy acquired and . These two U-boats were stationed in Portsmouth, Virginia, but they were not commissioned in the Navy. During November 1946 President Harry S. Truman visited U-2513; the submarine dived to with the President aboard. In 1947 the two submarines were allocated to an operational development force and underwent tests and trials. These tests and trials ended in the summer of 1948 for U-3008, U-2513 continued for another year before both submarines were used as targets for weapon trials. U-2513 was sunk as a target on 7 October 1951 by the destroyer . U-3008 was blown up in May 1952. ==Notable wrecks==

• On 3 May 1945 , , and were scuttled in the damaged "Elbe II" U-boat bunker in Hamburg. They were partially scrapped in 1950. It was intended to bury these U-boats under the remains of the bunker, but demolition attempts succeeded only in bringing the roof down on the U-boats. The bunker has since been filled in with sand and covered with earth. • U-2513 is in of water, west of Key West, Florida. The boat has been visited by divers, but the depth makes this very difficult and the site is considered suitable for only advanced divers. • Four other boats lie off the coast of Northern Ireland, where they were sunk during 1946 as part of Operation Deadlight. Both and were found by nautical archaeologist Innes McCartney during his Operation Deadlight expeditions between 2001 and 2003. • In April 2018 the wreck of was found north of Skagen in Denmark. ==Influences==

The Type XXI design directly influenced advanced post-war submarines: • The Greater Underwater Propulsion Power Program (GUPPY) improvements to the United States , and -class submarines • Several Soviet design projects, Projects 611, 613, 614, 633, and 644. These projects became known by their NATO codes as , and submarine classes. • The Chinese-built Romeo-class submarines, and the subsequent . • The British Porpoise-class submarine were the first post-war combat submarines built in Britain. Their design incorporated the lessons learned in the second World War, but also the results of the examinations of the captured Type XXIs. • The Swedish were neutral in World War II and did not gain much insight on contemporary submarine development. However, at the end of the war the Type XXI scuttled itself close to Gothenburg. The U-boat was subsequently raised and studied by the Swedish. Between 1957 and 1960, they produced six -class submarines which were at 720 tons much smaller, but had a Type XXI style hull and battery capacity. ==See also==