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{{Short description|Naval auxiliary ship}}
[[File:Sirius refueling Juneau.jpg|thumb|300px|The replenishment oiler {{HMAS|Sirius|O 266|6}} (right) providing fuel to the amphibious warfare ship {{USS|Juneau|LPD-10|6}} while both are underway]]
A '''replenishment oiler''' or '''replenishment tanker''' is a naval [[auxiliary ship]] with [[fuel tank]]s and dry [[cargo hold]]s which can supply both fuel and dry stores during [[underway replenishment]] (UNREP) at sea. Many countries have used replenishment oilers.

The [[US Navy hull classification symbol|United States Navy's hull classification symbol]] for this type of ship was 'AOR' (Auxiliary Oil Replenishment). Replenishment oilers are slower and carry fewer dry stores than the US Navy's modern [[fast combat support ship]]s, which carry the classification 'AOE'. In 2020 the US Navy began to develop a new type of ship, the 'AOL' or [[List of United States Navy oilers#Light Replenishment Oilers (T-AOL)|light replenishment oiler]]; construction of the first is planned for 2026.<ref name=USNI_20230428>{{cite news|title=Report to Congress on Navy Light Replenishment Oiler |date=April 2023 |url=https://news.usni.org/2023/04/28/report-to-congress-on-navy-light-replenishment-oiler |newspaper=USNI News |publisher=United States Naval Institute }}</ref>

==History==
[[File:RFA Tiderace Dual RAS with HMS Lancaster and HMS Westminster.jpg|thumb|left|{{ship|RFA|Tiderace|A137|6}} performing a dual repenishment of [[Royal Navy]] frigates {{ship|HMS|Lancaster|F229|6}} and {{ship|HMS|Westminster|F237|6}}.]]
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 station]]s or for warships to raft together with [[Collier (ship)|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 [[warship]]s 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 Ocean theater of World War II|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 replenishment|underway]] and for transporting highly combustible materials with increased effectiveness through hostile waters and over vast ocean distances.<ref>[http://www.usmm.org/tankers.html "Tankers Built in U.S. During World War II"], American Merchant Marine at War (usmm.org).  Retrieved June 9, 2017.</ref><ref>Sawyer, L. A.; Mitchell, W. H. (1974).  ''Victory ships and tankers; the history of the "Victory" type cargo ships and of the tankers built in the United States of America during World War II''.  Cornell Maritime Press, Cambridge, Maryland, 1974.</ref>

Modern examples of the [[fast combat support ship]] include the large British Fort class, displacing {{convert|31,066|LT}} and measuring {{convert|669|ft|m}} in length and the United States' {{sclass|Supply|fast combat support ship|0}} {{USNS|Arctic|T-AOE-8|6}}, which displaces {{convert|48,800|LT}} and has an [[Length overall|overall length]] of {{convert|754|ft|m}}.

==Characteristics==
[[File:Wabash Refueling Midway 1974.jpg|left|thumb|Replenishment oiler [[USS Wabash (AOR-5)|USS ''Wabash'']] at work]]
For all but the largest navies, replenishment oilers are typically one of the largest ships in the fleet. 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]]. These ships, when operating in concert with surface groups, can act as an 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 ship]]s, with some ships, such as the French {{sclass|Durance|tanker|4}}, this capability being built into the vessels from the start.

==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.

==Operators==
* {{navy|Argentina}} operates a single {{sclass|Durance|tanker|2}} purchased from France.
* {{navy|Australia}} operates two {{sclass|Supply|replenishment oiler|2}}s.
* {{navy|Brazil}} operates the [[Brazilian tanker Almirante Gastão Motta|''Almirante Gastão Motta'']]
* {{navy|Canada}} operates the {{MV|Asterix}}.
* {{navy|Chile}} operates a single {{sclass|Henry J. Kaiser|replenishment oiler|2}} purchased from the United States, and the [[Chilean oiler Araucano|''Araucano'']].
* {{navy|China}} operates two [[Type 901 fast combat support ship|''Fuyu''-class fast combat support ship]]s, four [[Type 904 general stores issue ship|''Dayun''-class general stores issue ship]]s, nine [[Type 903 replenishment ship|''Fuchi''-class replenishment ship]]s, and a single [[Type 908 replenishment ship|''Fusu''-class replenishment ship]].
* {{navy|Taiwan}} operates the [[ROCS Wu Yi (AOE-530)|ROCS ''Wu Yi'']] and [[Panshih-class fast combat support ship|ROCS ''Panshih'']]
* {{navy|Colombia}} operates two {{sclass|Lüneburg|replenishment ship|2}}s, purchased from Germany.
* {{navy|Egypt}} operates a single {{sclass|Lüneburg|replenishment ship|2}}, purchased from Germany (being supplemented or replaced by two [[Fort Rosalie-class replenishment ship]]s, purchased from the United Kingdom).
* {{navy|France}} operates one [[Bâtiment ravitailleur de forces|Jacques Chevallier-class]] and two {{sclass|Durance|tanker|2}}s
* {{navy|Germany}} operates six {{sclass|Elbe|replenishment ship|2}}s, two {{sclass|Rhön|tanker|2}}s, and three {{sclass|Berlin|replenishment ship|2}}s.
* {{navy|Greece}} operates a single {{sclass|Etna|replenishment oiler|2}} and two {{sclass|Lüneburg|replenishment ship|2}}s, purchased from Germany.
* {{navy|India}} operates two {{sclass|Deepak|fleet tanker|2}}s, one {{sclass|Aditya|auxiliary ship|2}}, and a single {{sclass|Komandarm Fedko|oiler|2}}.
* {{navy|Indonesia}} operates a single {{sclass2|Rover|tanker|2}} purchased from the United Kingdom, two ''Tarakan''-class tankers and more on order.
* {{navy|Italy}} operates a single {{sclass|Etna|replenishment oiler|2}} and two {{sclass|Stromboli|replenishment oiler|2}}s.
* {{navy|Iran}} operates two {{sclass|Bandar Abbas|replenishment ship|2}}s.
* {{navy|Japan}} operates three {{sclass|Towada|replenishment ship|2}}s and two {{sclass|Mashū|replenishment ship|2}}s.
* {{navy|South Korea}} operates three {{sclass|Cheonji|fast combat support ship|2}}s, and the [[ROKS Soyang (AOE-51)|ROKS ''Soyang'']]
* {{navy|Netherlands}} operates [[HNLMS Karel Doorman (A833)|HNLMS ''Karel Doorman'']]
* {{navy|New Zealand}} operates [[HMNZS Aotearoa|HMNZS ''Aotearoa'']].
* {{navy|Norway}} operates [[HNoMS Maud|HNoMS ''Maud'']].
* {{navy|Pakistan}} operates a single [[Type 905 replenishment tanker|''Fuqing''-class replenishment tanker]] and the [[PNS Moawin (A39)|PNS ''Moawin'']]
* {{navy|Peru}} operates the [[HNLMS Amsterdam (A836)|BAP ''Tacna'']]
* {{navy|Poland}} operates the [[ORP Bałtyk|ORP ''Bałtyk'']]
* {{navy|Russia}} operates three {{sclass|Boris Chilikin|fleet oiler|2}}s, one ''Dora''-class tanker, two ''Uda''-class tankers, one ''Iman''-class tanker, four ''Altay''-class tankers, three ''Dubna''-class tankers, two ''Kaliningradneft''-class tankers, and a single [[Project 23130 replenishment oiler]].
* {{navy|Saudi Arabia}} operates two {{sclass|Durance|tanker|2}}s.
* {{navy|South Africa}} operates the {{SAS|Drakensberg}}
* {{navy|Spain}} operates the {{ship|Spanish oiler|Patiño||2}} and {{ship|Spanish replenishment oiler|Cantabria||2}}.
* {{navy|Thailand}} operates the [[HTMS Similan]]
* {{navy|Turkey}} operates two {{sclass|Akar|replenishment oiler|2}}<nowiki/>s and one [[TCG Derya (A-1590)|''Derya'' class]].
* [[File:British-Royal-Fleet-Auxiliary-Ensign.svg|30px|Royal Fleet Auxiliary ensign]] British [[Royal Fleet Auxiliary]] operates one {{sclass|Fort Victoria|replenishment oiler|2}}, four {{sclass2|Tide|tanker|2}}s and two {{sclass2|Wave|tanker|2}}s (maintained in reserve).
* {{flagicon|USA}} [[United States Military Sealift Command]] operates two {{sclass|John Lewis|replenishment oiler|2}}s, fifteen {{sclass|Henry J. Kaiser|replenishment oiler|2}}s, fourteen {{sclass|Lewis and Clark|dry cargo ship|2}}s, and two {{sclass|Supply|fast combat support ship|2}}s.
* {{navy|Uruguay}} operates a single {{sclass|Lüneburg|replenishment ship|2}} purchased from Germany
* {{navy|Venezuela}} operates the [[RBNV Ciudad Bolívar|RBNV ''Ciudad Bolívar'']]

===Former operators===

* {{navy|Philippines}} decommissioned [[BRP Lake Caliraya (AF-81)|BRP ''Lake Caliraya'']] in 2020.
* {{navy|Portugal}} decommissioned [[NRP Bérrio (A5210)|NRP ''Bérrio'']] in 2020. Two new Replenishment Oilers will be received until 2028.<ref>{{Cite web |title=Marinha vai propor ao próximo Governo a compra de mais dois submarinos |url=https://www.jn.pt/6178677755/marinha-vai-propor-ao-proximo-governo-a-compra-de-mais-dois-submarinos/ |access-date=2024-01-02 |website=Jornal de Notícias |language=pt}}</ref>
* {{navy|Ukraine}} decommissioned its only {{sclass|Boris Chilikin|fleet oiler|2}} in 2001.

==United States Navy oilers==
{{see|List of United States Navy oilers}}
[[File:USNS Big Horn.jpg|thumb|300px|right|[[USNS Big Horn (T-AO-198)|USNS ''Big Horn'' (T-AO-198)]] an underway replenishment oiler.]]
[[File:Sailors prepare to receive fuel from the fleet replenishment oiler USNS Yukon (T-AO 202) during a replenishment-at-sea. (48947870241).jpg|thumb|US sailors aboard the {{USS|Makin Island|LHD-8}} prepare to receive replenishment from the {{USNS|Yukon|T-AO-202}}]]
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|Underway Replenishment]] or UNREP.<ref>{{cite web | title= UnRep| url= http://www.phdnswc.navy.mil/Pages/What_We_Do/TestAndEvaluation/UnRep/Default.aspx| work= Naval Surface Warfare Center, Port Hueneme Division| publisher= US Navy| access-date=2009-04-10}}</ref> 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'''<ref>{{cite web | title= Fleet Oilers| url=http://www.ibiblio.org/hyperwar/USN/ships/ships-ao.html | work= Hyperwar| publisher=Ibiblio | date=2002-09-01| access-date=2009-04-13}}</ref> in the 20th century; under the current [[Military Sealift Command|MSC]] operation their full classification is listed as '''Fleet Replenishment Oilers'''.<ref name="ffrep">{{cite web | title= Fleet Replenishment Oilers| url= http://www.navy.mil/navydata/fact_display.asp?cid=4400&tid=600&ct=4| work= US Navy Fact File| publisher=US Navy | date=2007-08-22 | access-date=2009-04-10}}</ref> 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<ref name="fffo">{{cite web | title= Fleet Oilers| url=http://www.ibiblio.org/hyperwar/USN/ships/ships-ao.html | work= HyperwarUS Navy Fact File| publisher=Ibiblio | date=2002-09-01| access-date=2009-04-13}}</ref> were identified by the hull designation AO, which is still in use.<ref name="ffrep"/> Large, fast multifunction oilers which also provide ammunition and dry stores are identified as [[Fast Combat Support Ship]]s (AOE),<ref name="ffcss">{{cite web | title= Fast Combat Support Ships| url= http://www.navy.mil/navydata/fact_display.asp?cid=4400&tid=300&ct=4| work=US Navy Fact File | publisher= US Navy| date= 2007-08-22| access-date=2009-04-10}}</ref> 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).

===Current classes===

There are three classes of vessels currently in commissioned service:

* [[Henry J. Kaiser-class replenishment oiler|''Henry J. Kaiser'' class]] 
* [[John Lewis-class replenishment oiler|''John Lewis'' class]]
* [[Supply-class fast combat support ship|''Supply'' class]]

Both the Henry J. Kaiser-class and Supply class will be replaced by the John Lewis-class ships.

==References==

{{reflist}}

==External links==
*[http://navysite.de/aor/aor6.htm DANFS USS KALAMAZOO (AOR-6) website]
*[http://www.nvr.navy.mil/ US Naval Vessel Register]
*[http://www.german-navy.de/kriegsmarine/ships/auxships/dithmarschen/ KMS Dithmarschen]
*[http://www.naval-technology.com/projects/patino/ Spanish Navy Patino Class AOR]
*[http://www.navy.gov.au/hmas-success HMAS Success, AOR-304]

{{Commons category|Oilers}}

{{Warship types of the 19th & 20th centuries}}
{{MARCOMships}}

[[Category:Ship types]]
[[Category:Auxiliary ships]]