German submarine U-309 was a Type VIIC U-boat of the Nazi German Kriegsmarine during World War II. The submarine was laid down on 24 January 1942 at the Flender Werke yard at Lübeck, launched on 5 December 1942, and commissioned on 27 January 1943 under the command of Oberleutnant zur See Hans-Gert Mahrholz. She sailed on nine combat patrols, but damaged only one ship, before being sunk off Scotland on 16 February 1945.