German submarine U-3509 was a Type XXI U-boat of Nazi Germany's Kriegsmarine during World War II. The Elektroboote submarine was laid down on 29 July 1944 at the Schichau-Werke yard at Danzig, launched on 27 September 1944, and commissioned on 29 January 1945 under the command of Oberleutnant zur See Karl-Heinz Voswinkel.