German submarine U-3505 was a Type XXI submarine of Nazi Germany's Kriegsmarine during World War II. The U-boat was laid down on 9 July 1944 at the Schichau-Werke yard at Danzig, launched on 25 August 1944, and commissioned on 7 October 1944 under the command of Oberleutnant zur See Horst Willner.
Like all Type XXI U-boats, U-3505 had a displacement of 1621t when at the surface and 1819t while submerged. She had a total length of 76.7m (251.6feet) (o/a), a beam of 8m (26feet), and a draught of 6.32m (20.73feet). The submarine was powered by two MAN SE supercharged six-cylinder M6V40/46KBB diesel engines each providing 4000lk=onNaNlk=on, two Siemens-Schuckert GU365/30 double-acting electric motors each providing 5000PS, and two Siemens-Schuckert silent running GV232/28 electric motors each providing 226PS.
The submarine had a maximum surface speed of and a submerged speed of . When running on silent motors the boat could operate at a speed of . When submerged, the boat could operate at for ; when surfaced, she could travel at . U-3505 was fitted with six 53.3cm (21inches) torpedo tubes in the bow and four 2sp=usNaNsp=us 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.
Although never used in combat, the submarine achieved some degree of fame due to a rescue mission. Her commander, Captain Horst Willner, disguised his wife as a sailor and smuggled her aboard together with their three-month-old baby (a crime punishable by death). The captain's family was originally to be evacuated on, joining a flood of refugees fleeing East Prussia ahead of the advancing Red Army, in "Operation Hannibal". Willner cancelled their places and took them onto his submarine, and so probably saved their lives since Gustloff was sunk by the with the greatest loss of life in maritime history.
After leaving Danzig they went to Gotenhafen, where they took on board 110 children and adolescents. The refugees, including the captain's family, were safely delivered at Travemünde, Lübeck on 2 April 1945.
Returning to Kiel, U-3505 was to participate in torpedo exercises, but on 3 April was sunk in a bombing raid while in harbour. At least one sailor was killed.