Replenishment oiler

A replenishment oiler is a naval auxiliary ship with fuel tanks and dry cargo holds, which can replenish other ships while underway on the high seas. Several countries have used replenishment oilers.

The US Navy hull classification symbol for this type of ship was AOR. Replenishment oilers are slower and carry fewer dry stores than the US Navy's fast combat support ships (AOEs).

History
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 world wide.

The forerunner of the modern replenishment oiler was a Kriegsmarine (German Navy) ship, the Dithmarschen, which was built in 1938. The Dithmarschen was designed to provide both fuel and stores (including munitions) to the German fleet. After World War II she was claimed by the United States as a war prize and commissioned into the United States Navy as the USS Conecuh (AOR-110). The ship proved the feasibility and flexibility of this sort of vessel in supporting task forces at sea.

The fast combat support ship (AOE) was developed first by the United States Navy as a logistics support vessel for aircraft carrier task forces, but the resulting vessel, while capable of high speed and of maintaining station as a component in the task force, was at the time the most expensive auxiliary ship ever procured by the United States Navy. For other applications not requiring high speed, such as anti-submarine groups, a smaller, less capable but much less expensive variant was desirable. This variant was the Wichita-class AOR.

Characteristics
For smaller navies, such as the Royal Canadian Navy, replenishment oilers are typically one of the largest ships in the navy. Such ships are designed to carry large amounts of fuel and dry stores for the support of naval operations far away from port. Replenishment oilers are also equipped with more extensive medical and dental facilities than smaller ships can provide.

Such ships are equipped with multiple refueling gantries to refuel and resupply multiple ships at a time. The process of refueling and supplying ships at sea is called underway replenishment. Furthermore, such ships often are designed with helicopter decks and hangars. This allows the operation of rotary-wing aircraft, which allows the resupply of ships by helicopter. This process is called vertical replenishment. Furthermore, such ships, when operating in concert with surface groups, can act as the aviation maintenance platform where helicopters receive more extensive maintenance than can be provided by the smaller hangars of the escorting ships.

Armament
Because the replenishment oiler is not a combat unit, but rather a support vessel, such ships are often lightly armed, usually with self-defense systems (such as the Phalanx CIWS close-in weapons systems), small arms, machine guns and/or light automatic cannons. They may also carry man-portable air-defense systems for additional air defense capability.

Examples
Replenishment oilers include:
 * Durance class (French Navy)
 * Preserver and Protecteur classes (Royal Canadian Navy)
 * Boris Chilikin type (Soviet Navy/Russian Navy)
 * Fort Victoria (Royal Navy)
 * (United States Navy)
 * Berlin class (German Navy)
 * Etna class (Italian Navy)
 * SPS Patiño and SPS Cantabria (Spanish Navy)
 * Fusu-class replenishment ship, Fuqing class replenishment ship and Qiandaohu class (People's Liberation Army Navy of China)
 * SAS Drakensberg (A301) (South African Navy)

The Canadian Navy (see Joint Support Ship Project) and the Spanish Navy are actively designing and building replenishment oilers.