If the story of the sinking of the Bismarck in 1941 is well known, the fate of sister ship the Tirpitz is less familiar. As the vessel lay anchored in Nazi-occupied Norway, a novel way was found to attack her. After human torpedoes failed, four-man midget submarines or X-craft carrying four-ton charges were used to penetrate the fjord defences. Six craft attacked on September 22, 1943.