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. For ships lost at sea, see list of shipwrecks in 1921 instead.
| Date | Operator | Ship | Pennant | Class and type | Notes |
| May 9 | ' | Modified destroyer | Scrapped | ||
| July 17 | A-3 | SS-4 | at Cavite Navy Yard, Philippines, disposed of as a target ship and stricken in 1922 | ||
| July 25 | A-5 | SS-6 | at Cavite Navy Yard, Philippines, disposed of as a target ship and stricken in 1922 | ||
| October 6 | ' | SP-418 | Patrol vessel | Tender and houseboat 1924-1933; Sold 1933 | |
| November 15 | ' | Modified destroyer | Scrapped | ||
| December 1 | ' | Seaplane tender and training ship | date stricken; later scrapped | ||
| December 12 | ' | Scuttled in 1924 | |||
| unknown date | ' | SP-680 | Patrol vessel/minesweeper | Sold |