A replenishment oiler or replenishment tanker is a naval auxiliary ship with fuel tanks and dry cargo holds which can supply both fuel and dry stores during underway replenishment (UNREP) at sea. Many countries have used replenishment oilers.
The United States Navy's hull classification symbol for this type of ship was AOR. Replenishment oilers are slower and carry fewer dry stores than the U.S. Navy's modern fast combat support ships, which carry the classification AOE.
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 the First World War. 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 the Second World War, the United States Navy's dramatically enlarged fleets, especially those in the Pacific Theater, required massive quantities of black oil, diesel oil, avgas, 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.
Modern examples of the fast combat support ship include the large British Fort class, displacing 31,066 long tons (31,565 t) and measuring 669 feet (204 m) in length; the Australian HMAS Sirius; and the United States' Supply-class USNS Arctic, which displaces 48,800 long tons (49,600 t) and has an overall length of 754 feet (230 m).
For smaller navies, such as the Royal New Zealand 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.
Their size, additional facilities, and ability to support the operation of other vessels, means that replenishment oilers have been used as command ships, with some ships, such as the French Durance-class, this capability being built into the vessels from the start.
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.
Replenishment oilers include:
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 Akar class is a series of replenishment oilers and fleet support ships, originally designed and built for service in the Turkish Navy.Beiyou 572-class replenishment oiler
Beiyou 572 class oil tanker is a class of naval auxiliary ship currently in service with the People's Liberation Army Navy (PLAN). The name of this class is after the first unit commissioned, with the exact type still remains unknown, and a total of four of this class have been confirmed in active service as of mid-2010s.Beiyou 572 class series ships in PLAN service are designated by a combination of two Chinese characters followed by three-digit number. The second Chinese character is You (油), meaning oil in Chinese, because these ships are classified as oil tankers. The first Chinese character denotes which fleet the ship is service with, with East (Dong, 东) for East Sea Fleet, North (Bei, 北) for North Sea Fleet, and South (Nan, 南) for South Sea Fleet. However, the pennant numbers may have changed due to the change of Chinese naval ships naming convention.Boraida-class replenishment oiler
The Boraida class is a ship class of two replenishment oilers built for the Saudi Navy by CN la Ciotat, Marseille. It is a modified version of the Durance-class replenishment ship.Cimarron-class fleet replenishment oiler
The Cimarron class was a class of five replenishment oilers which served in the United States Navy between 1981 and 1999. These ships were sized to provide two complete refuelings of a fossil-fueled aircraft carrier and six to eight accompanying destroyers. All five of the class were jumboized in 1990-92 by being cut in two and a 108-foot (35.7 m) section inserted, increasing their capacities from 120,000 bbls to 180,000 bbls, adding capacity for 300 tons of munitions and improving underway replenishment capabilities. The class was retired in 1998-99 after less than 20 years of service as a result of post-Cold War force reductions, and the advent of the more economical diesel-powered Henry J. Kaiser-class oilers.Cimarron-class oiler (1939)
The Cimarron-class oilers were an underway replenishment class of oil tankers which were first built in 1939 as "National Defense Tankers," United States Maritime Commission Type T3-S2-A1, designed "to conform to the approved characteristics for naval auxiliaries in speed, radius and structural strength", anticipating their militarization in the event of war. "Tentative plans had been reached with the Standard Oil Company of New Jersey to build ten high-speed tankers with the government paying the cost of the larger engines needed for increased speed. By the first week in December , Standard Oil had solicited and received bids from a number of yards providing for the construction of a number of 16,300-ton (deadweight) capacity tankers. Bids were requested for two versions: a single-screw design of 13 knots and a twin-screw design of 18 knots. The price difference between the two would be used to establish the government's cost subsidy for greater speed. Plans and specifications for both designs were prepared for Standard Oil by naval architect E. L. Stewart. It seems certain that the design for the 18-knot tanker (Standard Oil Co. of New Jersey Design No. 652 NDF) evolved out of the bureau's (C&R) design for a fleet oiler." Three of the original twelve ships were commissioned directly into the Navy at launch in 1939; the remainder entered merchant service with Standard Oil of New Jersey and Keystone Tankships before being acquired under the Two-Ocean Navy Act of July 1940. A further eighteen were built for the Navy between 1943 and 1946, with five additional units, sometimes called the Mispillion class, built to the slightly larger Type T3-S2-A3 design.
Four of the Cimarrons were converted to escort carriers in 1942; two others were sunk by enemy action.Durance-class tanker
The Durance class is a series of multi-product replenishment oilers, originally designed and built for service in the French Navy. Besides the five ships built for the French Navy, a sixth was built for the Royal Australian Navy, while the lead ship of the class currently serves with the Argentine Navy.
They will be replaced under the FLOTLOG project by four derivatives of Italy's Vulcano Logistic Support Ship, scheduled to be delivered in 2022, 2025, 2027 and (subject to ratification of the next procurement plan) 2029.Escambia-class oiler
The Escambia-class oilers were a class of twelve T2-SE-A2 tankers that served in the United States Navy, built during World War II. The ships were named for United States rivers with Native American names. They were very similar to the Suamico class (of which they are sometimes accounted a subclass), differing principally in having the more powerful turboelectric plant of the P2-SE2 transports which developed 10,000 shp.
All of the ships were decommissioned and transferred to the Military Sea Transportation Service in the post-war period. Several were later transferred to the United States Army and converted to floating electricity generating stations, and served in that role in Vietnam.Etna-class replenishment oiler
Etna-class is a ship class of two naval replenishment and logistic support ships used by the Italian Navy and by the Greek Navy The two ships are almost identical but they have differences in their armament and sensor equipment.Fort Victoria-class replenishment oiler
The Fort Victoria or Fort II class is a class of replenishment oiler of the Royal Fleet Auxiliary, a role that combines the missions of a tanker and stores supply ship. As such they are designated auxiliary oiler replenisher (AOR). They are tasked with providing ammunition, fuel, food and other supplies to Royal Navy vessels around the world. There are two ships in the class, Fort Victoria and Fort George, the latter being taken out of service and despatched for scrapping at a Turkish breakers as a consequence of budgetary cutbacks across the Royal Navy.HMAS Supply
Two ships of the Royal Australian Navy (RAN) have been named HMAS Supply.
HMAS Supply (AO 195), an Tide-class replenishment oiler launched on 1 September 1954 into the Royal Fleet Auxiliary and commissioned on 15 August 1962 into the Royal Australian Navy, decommissioned on 16 December 1985.
HMAS Supply (A 195), a replenishment oiler is the lead ship in the new Supply-class AOR based on the Cantabria-class oiler. The keel was laid down by Navantia on 17 November 2017, and Supply was launched on 23 November 2018.HMCS Provider (AOR 508)
HMCS Provider was a replenishment oiler and sole ship of her class of first the Royal Canadian Navy and later the Canadian Forces. She was the first dedicated auxiliary oiler replenishment ship commissioned for the Royal Canadian Navy in 1963, and the largest ship built in Canada to that date. Originally assigned to the East coast, her open deck made her vulnerable and she was reassigned to the West coast. The ship was paid off in 1998, sold for scrap and broken up in Turkey in 2003.Henry J. Kaiser-class replenishment oiler
The Henry J. Kaiser class is an American class of eighteen fleet replenishment oilers which began construction in August 1984. The class comprises fifteen oilers which are operated by Military Sealift Command to provide underway replenishment of fuel to United States Navy combat ships and jet fuel for aircraft aboard aircraft carriers at sea. One ship, operated by the United States from 1987 to 1996, was sold to Chile in 2009 and commissioned into the Chilean Navy in 2010; and two ships were scrapped in 2011 while still incomplete.
Twelve of the Kaisers are not double-hulled like most modern tankers; the class will be replaced under the TAO(X) project which will build 20 double-hulled ships, starting with USNS John Lewis and USNS Harvey Milk.Patoka-class oiler
The Patoka-class oilers were a series of eight fleet replenishment oilers built for the United States Navy after World War I. All but one of the vessels were commissioned between 1919 and 1922, and all were held in various states until the eve of World War II, where all served with the Navy for the duration of the war. All eight survived the war, after which they were decommissioned and scrapped.Protecteur-class replenishment oiler
The Protecteur-class auxiliary oiler replenishment (AOR) ships were used by the Royal Canadian Navy to resupply ships at sea with food, munitions, fuel and spare parts. They had more sophisticated medical and dental facilities than smaller warships. At 172 metres (564 ft) the ships were the largest operated by the RCN. Entering service in 1969, the last vessel of the class was paid off in 2016.Stromboli-class replenishment oiler
The Stromboli class is a series of two replenishment oilers used by the Marina Militare since 1975. They are to be replaced by the Vulcano class beginning in 2019.The ships are capable of loading:
4.000 t (3.937 long tons) of NATO F76 diesel fuel
400 t (390 long tons) of NATO F44/JP5 aviation fuel
300 t (300 long tons) of solid goodsTide-class replenishment oiler
The Tide class was a series of six replenishment oilers used by the British Royal Fleet Auxiliary (RFA), the Royal Australian Navy (RAN), and the Chilean Navy.
The class was based on RFA Olna, which had served with the British Pacific Fleet during World War II. Three ships were laid down for the RFA in 1953, with a fourth being ordered by the RAN at the same time. Two more ships, built for the RFA to a modified design, were launched in 1962.
Upon completion, the Australian Tide Austral could not be accepted into service because of manpower and financial difficulties. The ship was instead loaned to the RFA from 1955 until 1962, when she was returned to the RAN and commissioned as HMAS Supply. She was paid off in 1985.The first three ships were removed from service and scrapped during the late 1970s. The two modified ships, Tidespring and Tidepool saw service in the Falklands War, after which Tidepool was sold to the Chilean Navy and renamed Almirante Jorge Montt. Tidespring remained with the RFA and was scrapped in 1992. Supply remained with the RAN until 1985.USNS John Lewis (T-AO-205)
USNS John Lewis (T-AO-205) is a United States Navy replenishment oiler and the lead ship of her class. She is part of the Military Sealift Command fleet of support ships.USS Saugatuck
USS Saugatuck (AO-75) was a Suamico-class replenishment oiler of the United States Navy.
The ship was laid down on 20 August 1942 as SS Newtown, a Maritime Commission type Type T2-SE-A1 tanker hull, under Maritime Commission contract (MC hull 355) at the Sun Shipbuilding & Drydock Co., Chester, Pennsylvania. She was renamed Saugatuck on 16 September 1942. Launched on 7 December 1942, and delivered to the U.S. Navy, she was converted for naval service at Bethlehem Steel Co., Key Highway Plant, Baltimore, Maryland. She was commissioned on 19 February 1943, with Lt. Comdr. Ben Koerner, USNR, in command. It was named for the Saugatuck River in Connecticut.Wichita-class replenishment oiler
Wichita-class replenishment oilers comprised a class of seven replenishment oilers used by the United States Navy from the late 1960s to the mid-1990s. The ships were designed for rapid underway replenishment using both connected replenishment and vertical replenishment.
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World War II Maritime Commission ship designs