Type XXI submarine
Type XXI submarines were a class of German diesel–electric Elektroboot submarines designed during the Second World War. One hundred and eighteen were commissioned, but only one executed a combat patrol in the last week of the war.
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 of escaping detection. They incorporated many batteries to increase the time they could spend submerged, to as much as several days, and they only needed to surface to periscope depth for recharging via a snorkel. The design included many general improvements as well: much greater underwater speed by an improved hull design, greatly improved diving times, power-assisted torpedo reloading and greatly improved crew accommodations. However, the design was also flawed in many ways, with the submarines being mechanically unreliable and, according to post-war analysis, vulnerable to combat damage. The Type XXI submarines were also rushed into production before design work was complete and the inexperienced factories which constructed the boats were unable to meet quality standards.
After the war, captured Type XXIs were examined by several navies, and many post-war submarine design were influenced by them. These include the Soviet, Chinese Ming, American, British Porpoise, and Swedish classes.
Design
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 for 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 but its submerged speed was more than twice that of the Type IX 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, made the Type XXI much more difficult to pursue and destroy. It could sprint when positioning for an attack. 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. The Type XXIs also 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 electrical powered trolley could push the torpedo much faster in the torpedo tube as had been possible with the manual reloading process. 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 four torpedoes for twelve mines. Four torpedo tubes could contain three mines each and eject these mines with pressured 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 arragenement 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 sound listening gear 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 eighth 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 sections were made by companies having little experience with shipbuilding.