Submarines are small compared to most oceangoing vessels, and generally do not have the ability to carry large amounts of food, fuel, torpedoes, and other supplies, nor to carry a full array of maintenance equipment and personnel. The tender carries all these, and either meets submarines at sea to replenish them or provides these services while docked at a port near the area where the submarines are operating. In some navies, the tenders were equipped with workshops for maintenance, and as floating dormitories with relief crews.
Canada's first Submarine Depot Ship was HMCS Shearwater
The term used in the Chilean Navy is "submarine mother ship", as for example the BMS (buque madre de submarinos) Almirante Merino.
The Russian Navy decommissioned all its Don and Ugra-class tenders inherited from the Soviet Navy by 2001. The last remaining ship of this class was INS Amba , initially sold to the Indian Navy in 1968 for use with their fleet of Foxtrot-class submarines. She was reportedly decommissioned in July 2006.
The Royal Netherlands Navy has one submarine support vessel, the HNLMS Mercuur , commissioned in 1987, as a replacement of the HNLMS Onverschrokken , then known as the HNLMS Mercuur (A 856). Commissioned in 1956, as an ocean going Aggressive-class minesweeper, built in the US, and later used as a submarine tender.
In the United States Navy, submarine tenders are considered auxiliaries, with hull classification symbol "AS". As of 2017 , the Navy maintains two such tenders, USS Emory S. Land and USS Frank Cable .
List of Royal Navy submarine tenders