German submarine U-3506 was a Type XXI U-boat of Nazi Germany's Kriegsmarine during World War II.

The Elektroboote submarine was laid down on 14 July 1944 at the Schichau-Werke yard at Danzig, launched on 28 August 1944, and commissioned on 16 October 1944 under the command of Kapitänleutnant Gerhard Thäter.

[2] The submarine was powered by two MAN SE supercharged six-cylinder M6V40/46KBB diesel engines each providing 4,000 metric horsepower (2,900 kilowatts; 3,900 shaft horsepower), two Siemens-Schuckert GU365/30 double-acting electric motors each providing 5,000 PS (3,700 kW; 4,900 shp), and two Siemens-Schuckert silent running GV232/28 electric motors each providing 226 PS (166 kW; 223 shp).

[3] The bunker has since been filled in with gravel, although even that did not initially deter many souvenir hunters who measured the position of open hatches and dug down to them to allow the removal of artifacts.

The site is located in the Free Port of Hamburg and in order to access it one must present a passport.