Heal outside of friendly territory.

While one may have some limited combat (usually defensive) capability, in general auxiliary ships are those that keep the real combat ships functioning at peak efficiency. Without the auxiliaries, no blue-water navy can be efficient, successful, or often afloat. As European navies began to range the oceans during the 1700s and 1800s, those big men-of-war needed support vessels to replenish supplies, make repairs away from ports, and guard those naval bases scattered about the globe. When the age of steam dawned, colliers and later oilers kept the boilers in the destroyers and battleships firing. As navies became ever more diverse, so too did the auxiliary ships; the modern U.S. Navy lists some 86 different types (not counting floating repair docks).