List of ship decommissionings in 1921
# List of ship decommissionings in 1921

The list of ship commissionings in 1921 includes a chronological list of ships commissioned in 1921. In cases where no official commissioning ceremony was held, the date of service entry may be used instead.

| Date | Operator | Ship | Pennant | Class and type | Notes |
| - | - | - | - | - | - |
| May 9 | Royal Navy | Tristram | | Modified R-class destroyer | Scrapped |
| July 17 | United States Navy | A-3 | SS-4 | Plunger-class submarine | at Cavite Navy Yard, Philippines, disposed of as a target ship and stricken in 1922 |
| July 25 | United States Navy | A-5 | SS-6 | Plunger-class submarine | at Cavite Navy Yard, Philippines, disposed of as a target ship and stricken in 1922 |
| October 6 | United States Navy | Aramis | SP-418 | Patrol vessel | Tender and houseboat 1924-1933; Sold 1933 |
| November 15 | Royal Navy | Tirade | | Modified R-class destroyer | Scrapped |
| December 1 | French Navy | Foudre | | Seaplane tender and training ship | date stricken; later scrapped |
| December 12 | Royal Australian Navy | Australia | | Indefatigable-class battlecruiser | Scuttled in 1924 |
| unknown date | United States Navy | Ardent | SP-680 | Patrol vessel/minesweeper | Sold |
