[3] Between 9 November 1941 and 31 March 1942, K-21 unsuccessfully engaged three merchant ships and one German auxiliary patrol vessel.

[4] 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.

Later, the submarine received a radiogram telling that a German squadron consisting of the battleship Tirpitz, the heavy cruiser Admiral Scheer, and several destroyers were moving to intercept the PQ-17 convoy.

The first ships to be seen were destroyers of the 1936 class, and they covered Tirpitz and the cruiser Admiral Scheer from possible attacks from submarines.

In the spring of 1981, she was moved to the city of Polyarny, Murmansk Oblast to be converted into a museum ship.

After reworking three compartments for the exposition (the other 4 remained virtually unchanged) was put on a pedestal (immersed in water at high tide) as a museum in Severomorsk, Russia.

On 14 September 1943 other three small Norwegian fishing boats (Havatta, Baren and Eyshteyn) were attacked with gunfire but escaped despite damage.