two Allied convoys. Convoy PQ 17, which left Iceland on 27 June bound for the Soviet Union, was the next convoy targeted by Tirpitz and the rest of the German fleet stationed in Norway, during Unternehmen Rösselsprung (Operation Knight's Move). Escorting the convoy were the battleships Duke of York and and the carrier Victorious. Tirpitz, , and six destroyers sortied from Trondheim, while a second task force consisting of , Admiral Scheer, and six destroyers operated from Narvik and Bogenfjord. Lützow and three of the destroyers struck uncharted rocks while en route to the rendezvous and had to return to port. Shortly after Tirpitz left Norway, the Soviet submarine K-21 fired two or four torpedoes at the ship, all of which missed. The Soviets claimed two hits on the battleship. Swedish intelligence had meanwhile reported the German departures to the British Admiralty, which ordered the convoy to disperse. Aware that they had been detected, the Germans aborted the operation and turned over the attack to U-boats and the Luftwaffe. The scattered vessels could no longer be protected by the convoy escorts, and the Germans sank 21 of the 34 isolated transports. Tirpitz returned to Altafjord via the Lofoten Islands. Following Rösselsprung, the Germans moved Tirpitz to Bogenfjord near Narvik. By this time, the ship needed a major overhaul. Hitler had forbidden the ship to make the dangerous return to Germany, and so the overhaul was conducted in Trondheim. On 23 October, the ship left Bogenfjord and returned to Fættenfjord outside Trondheim. The defences of the anchorage were further strengthened; additional anti-aircraft guns were installed, and double anti-torpedo nets were laid around the vessel. The repairs were conducted in limited phases, so Tirpitz would remain partially operational for the majority of the overhaul. A caisson was built around the stern to allow the replacement of the ship's rudders. During the repair process, the British attempted to attack the battleship with two Chariot human torpedoes, but before they could be launched, rough seas caused them to break away from the fishing vessel which was towing them. By 28 December, the overhaul had been completed, and Tirpitz began sea trials. She conducted gunnery trials on 4 January 1943 in Trondheim Fjord. On 21 February, Topp was promoted to Rear Admiral and was replaced by Captain Hans Meyer; five days later the battleship Scharnhorst was ordered to reinforce the fleet in Norway. Vice Admiral