German submarine U-3506

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.

Design
Like all Type XXI U-boats, U-3506 had a displacement of 1621 t when at the surface and 1819 t while submerged. She had a total length of 76.70 m, a beam of 8 m, and a draught of 6.32 m. The submarine was powered by two MAN SE supercharged six-cylinder M6V40/46KBB diesel engines each providing 4000 PS, two Siemens-Schuckert GU365/30 double-acting electric motors each providing 5000 PS, and two Siemens-Schuckert silent running GV232/28 electric motors each providing 226 PS.

The submarine had a maximum surface speed of 15.6 kn and a submerged speed of 17.2 kn. When running on silent motors the boat could operate at a speed of 6.1 kn. When submerged, the boat could operate at 5 kn for 340 nmi; when surfaced, she could travel 15500 nmi at 10 kn. U-3506 was fitted with six 53.3 cm torpedo tubes in the bow and four 2 cm C/30 anti-aircraft guns. She could carry twenty-three torpedoes or seventeen torpedoes and twelve mines. The complement was five officers and fifty-two men.

Service history
U-3506 undertook no war patrols, with no ships sunk or damaged, remaining as a training vessel for the duration of the war. U-3506 was one of three Type XXI boats (along with GS U-2505 and GS U-3004) that were scuttled in the Elbe II U-boat bunker. 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 boat now lies beneath a car park and she and the other wrecks are completely inaccessible. The site is located in the Free Port of Hamburg and in order to access it one must present a passport.