Events
On This Day - August 21
| 1916 | G7 | Completed |
| 1938 | Undine (N48) | Completed |
| 1940 | Rorqual (N74) | HMS Rorqual sank unknown 5000 ton Italian supply ship by torpedo |
| 1942 | Unison (P43) | HMS Unison torpedoes and damages the Italian tanker Pozarica off Sivota, Greece. |
| 1944 | Vampire (P72) | HMS Vampire sinks three sailing vessels with gunfire off Mykonos Island, Greece. |
| 1944 | Virtue (P75) | HMS Virtue sinks two sailing vessels with gunfire off Cape Spatha, Crete, Greece. |
| 1944 | Tapir (P335) | Launched |
| 1944 | Votary (P29) | Launched |
