The World War II Soviet submarine L-21 belonged to the L-class or Leninets class of minelayer submarines. She was part of the last series (Group 4) of her class, having some improvements including more torpedo tubes. The commander during the war was Sergey S. Mogilevskiy.[1]
Before completion, L-21 was sunk by German aircraft in Leningrad on 24 May 1942. L-21 was later raised, completed and commissioned, making both torpedo attacks and mine-laying. Among her victims was the Hansa, a neutral Swedish passenger ship travering from Nynäshamn to Visby. 84 innocent people were killed in the attack, which is commemorated by a memorial plaque in Visby Cathedral on Gotland, where the ship's bell is also preserved.[2] L-21 also managed to sink a number of German warships, including two torpedo boats and a submarine.
| Date | Ship | Flag | Tonnage | Notes |
|---|---|---|---|---|
| 23 November 1944 | Eichberg | 1,923 GRT | freighter (mine) | |
| 24 November 1944 | Elie | 1,837 GRT | freighter (mine) | |
| 24 November 1944 |  | 563 GRT | passenger ship (torpedo) | |
| 22 December 1944 | Eberhard | 749 GRT | freighter (mine) (possibly) | |
| 14 March 1945 | T3 | 839 t displacement | torpedo boat (mine) | |
| 14 March 1945 | T5 | 839 t displacement | torpedo boat (mine) | |
| 16 March 1945 | 769 t displacement (surfaced) | submarine (mine) | ||
| 23 March 1945 | V 2022/E Colzmann | 581 GRT | patrol boat (torpedo) | |
| 24 March 1945 | Erni | 105 GRT | tug (torpedo) | |
| Total: | 8,205 GRT |
One of her mines heavily damaged the German destroyer Z43.