An oiler is a naval auxiliary ship that carries fuels to refuel other warships. Some navies classify oilers as tankers. If dry goods are also supplied, it is called a replenishment oiler.
The development of the "oiler" paralleled the change from coal- to oil-fired boilers in warships. Prior to the adoption of oil fired machinery, navies could extend the range of their ships either by maintaining coaling stations or for warships to raft together with colliers and for coal to be manhandled aboard. Though arguments related to fuel security were made against such a change, the ease with which liquid fuel could be transferred led in part to its adoption by navies worldwide.
One of the first generation of "blue-water" navy oiler support vessels was the British RFA Kharki, active 1911 in the run-up to World War I. Such vessels heralded the transition from coal to oil as the fuel of warships and removed the need to rely on, and operate within range of "coaling stations". During World War II, the United States Navy's dramatically enlarged fleets, especially those in the Pacific Theater, required huge quantities of bunker oil, Diesel fuel, aviation gasoline, and other fuels and lubricants to support American land, sea, and air operations against remote, widely dispersed Japanese forces. Those supply demands resulted in U.S. Navy personnel refining many established practices for oilers and creating new procedures for replenishing warships while underway and for transporting highly combustible materials with increased effectiveness through hostile waters and over vast ocean distances.[1][2]