United States Navy oiler

In the United States Navy, an Oiler is a Combat Logistics ship that replenishes other ships with fuel and in some cases food, mail, ammunition and other necessities while at sea, in a process called Underway Replenishment or UNREP. Up through the Second World War Navy oilers used commercial tanker hulls, with the addition of UNREP gear, defensive guns, and military electronic and damage-control equipment; since the 1950s however they have been built from the keel up as specialized naval auxiliaries. They were previously classified as Fleet Oilers in the 20th Century; under the current MSC operation their full classification is listed as Fleet Replenishment Oilers. Since the 1960s the classification Transport Oiler (AOT) has applied to tankers which ship petroleum products to depots around the world, but do not engage in UNREP.

The first fleet oilers were identified by the hull designation AO, which is still in use. Large, fast multifunction oilers which also provide ammunition and dry stores are identified as Fast Combat Support Ships (AOE), and mid-size ones Replenishment Oilers (AOR). The AOR designation is no longer in use. All of these oilers provide the combined services of the AO, AE, AFS and AK.

The style "USNS" and prefix "T" identify a ship as being operated by a civilian crew under the Military Sealift Command (known as the Military Sea Transportation Service until 1970).

Note: tonnages are given in naval light/full load displacement

Arethusa was built in Britain 1893 as the SS Luciline and was purchased in 1898, serving originally as a water carrier. In 1910 she was converted to carry fuel oil, mostly in support of destroyers: she thus became the Navy's first oiler. With the new hull designation system of 1920 she was redesignated AO-7.

The Navy's first fuel ships designed and built as oilers, rather than colliers, the Kanawha class comprised two ships commissioned just before World War I, which displaced 5,950/14,800 tons. Until 1920 they were designated "Fuel Ship No. 13" etc. Maumee was the first large US Navy vessel with diesel engines. In 1917 Maumee also became the first ship in the world to refuel others while underway in wartime conditions, and the first to do so in rough seas, having been positioned in the mid-Atlantic to aid the crossing of short-legged US destroyers to Britain under the supervision of her Chief Engineer, Lt. Chester W. Nimitz.

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