The list of ship commissionings in 1921 includes a chronological list of all ships commissioned in 1921.
| Operator | Ship | Flag | Class and type | Pennant | Other notes | |
|---|---|---|---|---|---|---|
| 27 April | 
Royal Netherlands Navy
|
K IV | K III-class submarine | K IV | ||
| 21 July | 
United States Navy
|
Maryland | Colorado-class battleship | BB-46 | ||
| 10 August |
United States Navy
|
California | Tennessee-class battleship | BB-44 | ||
| 11 October |
Royal Netherlands Navy
|
K VI | K V-class submarine | K VI | ||
| 16 December |
United States Navy
|
Salinas | Patoka-class oiler | AO-19 | ||
| Unknown | 
Chilean Navy
|
Almirante Latorre | Almirante Latorre-class battleship | Purchased from the Royal Navy |