A depot ship is an auxiliary ship used as a mobile or fixed base for submarines, destroyers, minesweepers, fast attack craft, landing craft, or other small ships with similarly limited space for maintenance equipment and crew dining, berthing and relaxation. Depot ships may be identified as tenders in American English. Depot ships may be specifically designed for their purpose or be converted from another purpose.

An auxiliary ship is a naval ship designed to support combatant ships and other naval operations. Auxiliary ships are not primary combatant vessels, though they may have some limited combat capacity, usually for purposes of self-defense.