December 8, 1943 U-305 sailed from Brest, France for a patrol in the North Atlantic, this was the forth patrol for the boat and her commander Kapitänleutnant Rudolf Bahr, who had been commanding officer since the boat was commissioned on Sept. 17, 1942.

On Jan. 7, 1944 he torpedoed and sank HMCS Tweed K-250, the last ship lost to U-305. A signal was sent to BdU on Jan. 15 from Bahr stating that he was returning to France, the reason for this was not given and the boat was never heard from again. Some sources claim she was sunk on Jan. 17, 1944 by HMS Wanderer D-74, but new research indicates that the boat lost to Wanderer was U-377. To this day the true reason for her loss and the exact location remain a mystery. Her hull still holds the fifty-one men who did not return.