List of ship commissionings in 1921
The list of ship commissionings in 1921 is 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.
| Operator | Ship | Flag | Class and type | Pennant | Other notes | |
| 27 April | ' | K IV | ||||
| 21 July | ' | BB-46 | ||||
| 10 August | ' | BB-44 | ||||
| 11 October | ' | K VI | ||||
| 16 December | ' | AO-19 | ||||
| Unknown | ' | Purchased from the Royal Navy |