Type XXI submarine

Type XXI submarines is a class of diesel–electricU-boats built for Nazi Germany'sKriegsmarine from 1943 to 1945 during the Second World War. The concept of Type XXI submarines emerged in 1943 when it became clear the Type VII and Type IX still being produced, had become obsolete and the designed successor Type XVIII still faced blocking problems with its new propulsion system. 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. As they incorporated many batteries to increase the time they could spend submerged, they were sometimes referred to as Elektroboote (German: "electric boats") in the German Navy. They were equipped with a snorkel, which allowed them to cruise at periscope depth on their diesel engines, and recharge their batteries without having to surface. The design included many general improvements as well: much greater underwater speed by an improved hull design, power-assisted torpedo reloading and better crew accommodations.

In order to speed up the delivery of the new U-boats, a new mass production method of assemblingprefabricated sections was introduced, and production began before design work was completed. The inexperienced factories which constructed the boats were unable to meet quality standards, and most of the produced U-boats were mechanically unreliable. The massive building program suffered also from the Allied Strategic bombing campaign. One hundred and eighteen Type XXIs were commissioned during the war, but only one executed a combat patrol in the last week of the war. After the war, captured Type XXIs were examined by several navies, and many post-war submarine designs were influenced by them. These include the Soviet Whiskey, Chinese Ming, American Tang, British Porpoise, and Swedish Hajen III classes.