An auxiliary ship is a naval ship which is designed to operate in any number of roles supporting combatant ships and other naval operations. Auxiliaries are not primary combatants, although they may have some limited combat capacity, usually of a self-defense nature.
Auxiliaries are extremely important for navies of all sizes, as without them, the primary fleet vessels can not be effective. Thus, nearly every navy maintains an extensive fleet of auxiliaries. However, the composition and size of these auxiliary fleets varies depending on the nature of each navy and its primary mission. Smaller coastal navies tend to have smaller auxiliary vessels focusing primarily on littoral and training support roles. Larger blue water navies tend to have large auxiliary fleets comprising longer-range fleet support vessels designed to provide support far beyond territorial waters.