The Type XXI is truly one of the great submarine designs. If it had come fully into service, it would have posed almost insuperable problems for the Allies. Even though it never became fully operational, it became the prototype for all future conventional submarines, and even influenced the design of the first nuclear submarines. 

Wilhelm Bauer (originally designated U-2540) is a Type XXI U-boat of Nazi Germany's Kriegsmarine, completed shortly before the end of World War II. Construction of U-2540 began on 28/29 October 1944 by Blohm & Voss in the Hamburg-Finkenwerder. She was launched on 13 January 1945 and commissioned on 24 February 1945 as part of 31st U-boat Flotilla for training purposes. In April 1945 the boat went to the front after training at Rønne on Bornholm. Due to the ongoing fuel shortages at the end of the war, the boat was relocated to Swinemünde before being scuttled near the Flensburg lightship on 4 May 1945.

The U-2540 was sunk in an air raid towards the end of the War... (read more at: http://www.submerged.co.uk/)