Throughout history there have been ships that have changed the course of Naval strategy and made previous types of ships obsolete overnight, the USS Monitor, the HMS Dreadnought and USS Nautilus are three, but add to the list the German Type XXI U-Boats which forever changed the way that submarines were built around the world.
The Type XXI was designed in 1943 in order to regain the initiative and thereby reassert German naval power in the Atlantic in order to turn the tide against the Allies. By 1943 the Allies had turned the tide against the Germans as the Type VII and Type IX U-Boats took heavy losses against naval units and convoys which now had air support at every stage of their trek across the North Atlantic. These boats had to surface for prolonged periods in order to recharge their batteries and had limited range, speed and endurance when submerged. The advent of the Escort Carrier, long range patrol bombers and hunter killer groups of Destroyers and the new Destroyer Escorts took a great toll on the U-Boat Force.
In order to meet the challenge the Germans opted for new technology based on the high speed hydrogen powered Walter turbines for underwater operations. Since these turbines which could produce a high underwater speed had a short endurance the designers modified the design to use conventional diesels but equip the boats with batteries that had three times the capacity of previous boats. The boats were a radical change from all previous submarine designs which were basically surface ships with the ability to operate underwater for limited periods of time. The Type XXIs were really the first true submarines. They could operate at underwater speeds that were faster than many of their opponents, had a streamlined design which facilitated higher submerged speed of 18 knots and silent running making them very difficult to track. They could remain underwater for 11 days while only needing 5 hours to recharge their batteries when using the schnorkel device.
The Type XXI had a full streamlined hull and conning tower and even equipment which were externally mounted such as the radio antennae, hydrophones, DF Ring and forward planes were fully retractable. They had no deck guns and their twin 20mm flak guns mounted in a streamlined housing on the conning tower. The German designers eliminated the traditional open bridge in favor of three small openings for the watch officer and 2 lookouts. They had a superior silent running ability and at 15 knots were quieter than the US Navy Balao Class doing 8 knots. They had a 1 inch thick steel aluminum alloy pressure hull with a designed crush depth of 280 meters (919 feet), a greater designed crush depth than any previous submarine.
They incorporated other innovations which would be incorporated into the post-war submarines of the victorious Allied powers. Among these innovations were semi-automatic hydraulic torpedo reload system which allowed three 6 torpedo salvos to be fired in less than 20 minutes where prior U-Boats had manual reloads and took over 10 minutes to reload a single torpedo. To make the fullest use of this capability the German equipped the boats with an advanced passive and active sonar system called the called Gruppenhorchgerät and Unterwasser-Ortungsgerät NIBELUNG mounted in the bow. The improved passive system enabled the boats to close to where they could emit short active sonar bursts to fix the target location. They could fire from a depth of 160 feet. The torpedoes themselves were an advanced design called the LUT or Lageunabhängiger Torpedo. The LUT was a guided torpedo that could be fired from the U-Boat regardless of the target’s bearing as it was programmed to steer an interception course programmed by the torpedo computer.
Submarines influenced by the Type XXI
The Type XXI boats were unique in production as they had no prototype and went directly in production. They were assembled from prefabricated sections built from factories around Germany and transported to the major shipbuilding yards. This was efficient but caused problems that slowed final assembly as many of the factories had no experience building U-Boats and quality suffered because the exacting specifications required by the Kriegsmarine. Likewise Allied air strikes on German factories and rail networks hampered production. Yet even in spite of these difficulties 119 Boats were completed although only four were rated as combat ready and only two were fully operational at war’s end. Of these only one embarked on a war patrol. Most were destroyed in air attacks while in port or scuttled by the Germans to prevent their capture. Eight Type XXIs were taken over by Allied navies at the end of the war where they were used to evaluate technology for use in future submarines. The U.S. Navy Tang Class boats were heavily influenced by the Type XXI as were the GUPPY upgrades to Balao and Tench class boats. The first nuclear submarines of the U.S. Navy, the Nautilus, Seawolf and the Skate Classes all incorporated design features of the Type XXIs. The Soviet Union developed its 613 and 614 project submarines which became the type known by NATO as the WHISKEY class from the Type XXIs that they received following Germany’s surrender. In 1957 the Federal Republic of Germany raised the scuttled U-2540 and commissioned her as the research submarine Wilhelm Bauer. That boat was operated by both the Bundesmarine and civilian crews until her decommissioning in 1982. She is now a museum ship open to the public in Bremerhaven.
The Type XXIs were the first true submarines and influenced every submarine constructed since. Though introduced too late in the war to make a difference they were truly a wonder-weapon.