HMS X-7, Imperial War Museum, London, 9 May 2017 1. X-7 was one of six midget submarines which successfully attacked the German batttleship Tirpitz in the Kafjord, in the far north of Norway, in September 1943. X-7 laid her two 2-ton mines under Tirpitz, but was herself sunk. Her commander was awarded the Victoria Cross and the three other crew members were also decorated, two of them posthumously. The attack put Tirpitz out of action for six months. After further attacks, she was finally sunk by Royal Air Force Lancasters in November 1944.