Submarines are relatively 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 up with the 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.
With the increased size and automation of modern submarines, plus their reliance on nuclear power, tenders are no longer as necessary as they once were.
The Russian Navy decommissioned all its Ugra class tenders inherited from the Soviet Navy by 2001. The last remaining ship of this class was the INS Amba (A54), initially sold to the Indian Navy in 1968 for use with their fleet of s. She was reportedly decommissioned from service in July 2006.