A repair ship is a naval auxiliary ship designed to provide maintenance support to warships. Repair ships provide similar services to destroyer, submarine and seaplane tenders or depot ships, but may offer a broader range of repair capability including equipment and personnel for repair of more significant machinery failures or battle damage.
The United States Navy became aware of the need for repair ships to maintain Asiatic Fleet ships stationed in the Philippines. Two colliers were converted to USS Prometheus and Vestal in 1913 before the purpose-built USS Medusa was completed at the Puget Sound Navy Yard in 1923.
These Xanthus-class repair ships were built to Royal Navy specifications by Bethlehem Fairfield Shipyard in 1944, but only the first two were temporarily loaned to the United Kingdom while the others were retained for use by the United States Navy:
Japan found repair ships valuable for Pacific island bases. The pre-dreadnought battleship Asahi was modified and recommissioned as a repair ship in 1938. The 9,000-ton purpose-designed repair ship Akashi was launched in 1938 as the intended prototype for a class of five ships, but the remaining four ships were cancelled as other wartime shipbuilding projects assumed higher priority.