The boat was laid on 10 December 1937 in Leningrad and launched on 16 August 1939. On 3 February 1941, it was commissioned as part of the Baltic Fleet under the command of Nikolai Lunin. On 17 September 1941, it was reenlisted in the Northern Fleet.
Service history
On its first war patrol, K-21 laid 11 mines in the Strait of Best-Sung. On the morning of27 November 1941, One of the mines struck and sank the Norwegian transport Bessheim. Between 9 November 1941 and 31 March 1942, K-21 unsuccessfully engaged three merchant ships and one German auxiliary patrol vessel. On 21 January 1942, Norwegian fishing boat F-223N Ingøy was sunk by gunfire from K-21.
Attack on ''Tirpitz''
On 5 July 1942, K-21 was in the vicinity of the Island of Ingay when she spotted the German battleship Tirpitz which was en route to intercept Convoy PQ 17 which was traveling from Iceland to Murmansk. However this mission was unsuccessful as the Tirpitz turned away. The convoy itself scattered upon hearing words of Tirpitz's imminent arrival, and most of the convoy's merchant ships were picked off by U-boats and the Luftwaffe. On 27 June 1942, the K-21 received an order to take up a combat position to cover Convoy PQ-17. Later, the submarine received a radiogram telling that a German squadron was moving to intercept the PQ-17 convoy. K-21 began to search for the enemy squadron. On 5 July, at 4:33 pm, noise of approaching propellers was heard. The squadron was anti-submarine zigzag. The first ships to be seen were destroyers of the 1936 class, they covered Tirpitz and the cruiser Admiral Scheer from possible attacks from submarines. The commander of K-21 decided to attack. K-21 bypassed the destroyers protective barrier and went inside the squadron. Having approached a distance of almost 13,000 feet, the submarine fired a four-torpedo spread from stern torpedo tubes towards the Tirpitz. Acoustics and crew members in the compartments of the submarine heard two explosions however, after the war, historians in German documents did not find evidence of torpedoes making contact with the battleship; the Germans did not even take notice of the attack. Historian M.E. Morozov put forward a hypothesis about the impossibility of torpedoes hitting the battleship, and he explained the origin of the explosions saying that the torpedoes detonated early. There are no references to Lunin's attack in the Tirpitz documents of the event. K-21 sank four small Norwegian motor boats via gunfire on 12 February 1943 at Lopphavet. On 22 April 1943, the German merchant shipDuna was sunk by a mine laid by K-21 on 18 February 1943. In May 1945, the boat was repaired.
Postwar
October 1948, K-21 made the first Soviet submarine voyage off the coast of the United States. From 6 to 14 April 1949 the boat took part in oceanographic work in the area of the Novaya Zemlya archipelago. After withdrawal from service, for about 20 years she served as a training ship. In the spring of 1981, she was moved to the city ofPolyarny, Murmansk Oblast to be converted into a museum ship. After reworking three compartments for the exposition was put on a pedestal as a museum in Severomorsk, Russia. The museum was opened in 1983. In the late 1990s, the boat underwent some general repairs. From 2008 to 2009, the museum was renovated.
