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 Kapitänleutnant Hans Hornkohl. With the end of the war near, training on U-boats had dropped to a minimum due to lack of fuel, falling morale and the effectiveness of allied attacks on U-boat construction and preparation. The exception to this were the new Type XXI boats, which continued to train in the Baltic Sea.