German submarine U-644

German submarine U-644 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on 1 December 1941 at the Blohm & Voss yard at Hamburg, launched on 20 August 1942, and commissioned on 15 October 1942 under the command of Oberleutnant zur See Kurt Jensen.

Attached to 5th U-boat Flotilla based at Kiel, U-644 completed her training period on 31 March 1943 and was assigned to front-line service.

Service history
In April 1943, U-644 was on patrol between the Shetlands and Jan Mayen. British signals intelligence had pinpointed the U-boat's position and HMS Tuna was dispatched to hunt down U-644. On 7 April, the Tuna detected the U-boat only 500 m away and fired a spread of five torpedoes. Two torpedoes hit U-644, which sank with all 45 crew members on board, there were no survivors.