Events
On This Day - June 21
| 1904 | A2 | Completed |
| 1916 | L3 | Laid Down |
| 1916 | L4 | Laid Down |
| 1929 | Poseidon (N99) | Launched |
| 1940 | H44 | HMS H 44 torpedoes and sinks the small Danish merchant Alfa off Texel, Netherlands. |
| 1942 | P514 | Sunk by accident in western Atlantic P514 was on passage around the coast of Newfoundland from Argentia to St Johns. On 20 June 1942 P514 left the Canadian village of Argentia bound for St Johns, Newfoundland. At 0300 on the 21st the Canadian minesweeper HMCS Georgian was waiting to provide escort for a convoy bound for Sydney. The Georgian, unaware that any friendly submarines were in the area, assumed that the dark shape of P514 crossing her bow, was an enemy vessel. The Georgian rammed the mystery submarine amidships and reported it sunk. A rescue mission was immediately sent out but no survivors were found. A Board of Enquiry into the accident accepted that the Commanding Officer of the Georgian had acted correctly as there had been no reply from the submarine to his identification challenge. |
| 1943 | Stratagem (P234) | Launched |
| 1944 | Universal (P57) | HMS Universal sinks the German Guardboat FMa 06 south of Marseille, southern France. |
| 1944 | Unsparing (P55) | HMS Unsparing sinks the German submarine chaser UJ 2106, the German barge Sybille and the German ferry SF 284 south of Cape Maleas, Greece. |
| 1944 | Aurochs (P426) | Laid Down |
| 1945 | L23 | HMS L23 paid off |
| 1950 | Sidon (P259) | Post refit diving trials were successfully completed. |
