German cruiser Leipzig

Leipzig in the Kaiser Wilhelm Canal in 1939

At the outbreak of World War II in September 1939, Leipzig was assigned to the blocking force that was intended to prevent the escape of the Polish Navy from the Baltic; they were unsuccessful. Leipzig thereafter went to the North Sea, where she and the other light cruisers laid a series of defensive minefields. This task lasted through the end of the month, after which she returned to the Baltic for training maneuvers.[5] On 17–19 November, Leipzig covered a minelaying operation in the North Sea. She joined Deutschland, Köln, and three torpedo boats for a sweep in the Skagerrak for Allied shipping on 21–22 November. Leipzig was tasked with escorting the battleships Scharnhorst and Gneisenau through the Skagerrak, and with covering their return on the 27th.[8]

On 13 December, Leipzig was tasked with escorting a flotilla of destroyers and other small vessels as they proceeded through the Skagerrak to lay a minefield. While en route, the British submarine HMS Salmon attacked the German warships, and at 11:25, hit Leipzig with a torpedo.[5] The torpedo hit Leipzig just below the waterline, where a bulkhead separated two of the ship's three boiler rooms. The explosion bent her armored deck and damaged her keel; some 1,700 t (1,700 long tons; 1,900 short tons) of water flooded the ship, and the damage cut electrical power to the ship's pumping system. The two boiler rooms were flooded, steam lines were damaged, and the port turbine was shut down. At around the same time, her sister Nürnberg was also torpedoed. A pair of destroyers arrived to escort the damaged cruisers back to port; an hour after Leipzig was torpedoed, one of the escorting destroyers was also torpedoed, just outside the mouth of the Elbe. Another torpedo passed just ahead of Leipzig, nearly hitting the damaged cruiser.[9] The following day, the Royal Air Force (RAF) launched an attack against Nürnberg and Leipzig.[10] Approximately 20 Vickers Wellington bombers from No. 99 Squadron were intercepted by fighters from II. Gruppe (2nd group) of Jagdgeschwader 77 (JG 77—77th Fighter Wing) under the leadership of Oberstleutnant Carl-Alfred Schumacher in the vicinity of Spiekeroog and Wangerooge. The RAF bombers failed to further damage the cruisers as JG 77 pilots claimed seven and one probable bomber shot down, including one claimed by Unteroffizier Herbert Kutscha. RAF records indicate that six bombers were lost in the attack.[11][12]

After safely returning to port in Kiel, Leipzig was taken into the Deutsche Werke shipyard for repairs. She was decommissioned while under repair and reclassified as a training ship. To accommodate additional training crews, four of the ship's boilers were removed. She returned to service in late 1940.[9] In early June 1941, she escorted the heavy cruiser Lützow (formerly Deutschland) to Norway. After she returned to the Baltic, she and the cruiser Emden provided artillery support to advancing German ground forces during Operation Barbarossa, the invasion of the Soviet Union.[13] In September, she supported the invasion of the Baltic islands in the West Estonian archipelago. While bombarding Soviet positions on Moon Island, Leipzig was attacked unsuccessfully by the Soviet submarine Shch-317.[14] In late September, the ship joined the German Baltic Fleet, centered on the battleship Tirpitz; the fleet was tasked with blocking a possible Soviet attempt to break out of the Baltic.[15] Leipzig returned to Kiel in October, and conducted maneuvers with the heavy cruiser Admiral Scheer. Leipzig became the flagship of the training fleet in 1942; she spent the year performing training duties.[13]

Leipzig was decommissioned briefly in March 1943, and recommissioned on 1 August. She was in need of an overhaul, however, and the work significantly delayed her return to operational status. Furthermore, an outbreak of meningitis killed two crewmen and created an additional delay. Leipzig returned to escort duties in the Baltic in mid-September 1944. Her first operation covered troop transports between Gotenhafen and Swinemünde in company with Admiral Scheer. On 14 October, Leipzig departed Gotenhafen, bound for Swinemünde, to take on a load of mines. In a heavy fog, she collided with the heavy cruiser Prinz Eugen, which was steaming at 20 knots (37 km/h; 23 mph). At the time of collision, Leipzig was switching from her diesel cruise engines to her steam turbine main engines, a process of first uncoupling the diesels from the shafts and then coupling turbines to the shafts, which left the ship temporarily without propulsion, drifting out of her fairway into the path of Prinz Eugen which was moving the opposite direction[16] Prinz Eugen struck Leipzig on her port side, just forward of her funnel, cutting her nearly in half - the forward point of the clipper bow of Prinz Eugen actually stuck out beyond the starboard side of Leipzig. The collision destroyed the number 3 (port) engine room, flooded a second engine room and killed or wounded 39 crewmen. The ships remained stuck fast for over a day, after which Leipzig was towed back to Gotenhafen.[17][18] The damage was so severe that repairs were deemed impractical, especially considering Germany's pressing military situation by late 1944. Only repairs to keep her afloat in the harbor were effected.[18]

Leipzig provided fire support to the defending German forces in March 1945, while Soviet Red Army forces advanced on the city. On 24 March, Leipzig was moved to Hela, laden with refugees; she was capable of steaming at only 6 knots (11 km/h; 6.9 mph). She was repeatedly attacked by Soviet aircraft, and Allied submarines attempted to torpedo her twice. She nevertheless safely reached Denmark on 29 April. Due to her poor state following the end of the war, she was used as a barracks ship for the men of the German Mine Sweeping Administration, tasked with clearing mines off the German coast. The battered ship was eventually towed out and scuttled in July 1946.[19]