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INS Deepak (left) conducting replenishment at sea with aircraft carrier INS Vikrant.
Fleet replenishment oiler USNS Patuxent

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' (Auxiliary Oil Replenishment). Replenishment oilers are slower and carry fewer dry stores than the US Navy's modern fast combat support ships, which carry the classification 'AOE'. In 2020 the US Navy began to develop a new type of ship, the 'AOL' or light replenishment oiler; construction of the first is planned for 2026.[1]

History

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RFA Tiderace performing a dual repenishment of Royal Navy frigates HMS Lancaster and HMS Westminster.

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.

The replenishment oiler HMAS Sirius (right) providing fuel to the amphibious warfare ship USS Juneau while both are underway

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.[2][3]

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 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).

Characteristics

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Replenishment oiler 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 ships, with some ships, such as the French Durance class, this capability being built into the vessels from the start.

Armament

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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

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Former operators

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United States Navy oilers

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Further information: List of United States Navy oilers
USNS Big Horn, an underway replenishment oiler.
US sailors aboard USS Makin Island prepare to receive replenishment from USNS Yukon

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.[5] 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[6] in the 20th century; under the current MSC operation their full classification is listed as Fleet Replenishment Oilers.[7] 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[8] were identified by the hull designation AO, which is still in use.[7] Large, fast multifunction oilers which also provide ammunition and dry stores are identified as Fast Combat Support Ships (AOE),[9] 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

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There are three classes of vessels currently in commissioned service:


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

References

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Replenishment oiler

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A replenishment oiler, also known as a fleet replenishment oiler or auxiliary oiler replenishment (AOR), is a naval auxiliary vessel designed to supply , provisions, , and other dry stores to warships and at sea through operations. These ships typically feature large tanks, cargo holds, and multiple replenishment stations—often up to five simultaneously—to transfer supplies via hoses, cables, or using helicopters, enabling naval task groups to maintain extended deployments without frequent calls. The practice of at-sea replenishment originated in primitive forms during the , with the first documented instance occurring in 1799 when the USS Constitution received supplies from a merchant vessel during the with France. Modern replenishment oilers emerged during , when the U.S. Navy converted commercial tankers into fleet oilers (AOs) to support Pacific operations, marking a shift from ad hoc methods to specialized vessels capable of high-speed, connected replenishment. Post-war advancements, including the development of alongside and astern refueling techniques in the 1950s, further refined these ships' roles, with designs emphasizing double-hull construction for safety and compliance with environmental regulations like the Oil Pollution Act of 1990. Replenishment oilers play a critical role in and , allowing carrier strike groups and expeditionary forces to operate far from home ports for months, as seen in U.S. Navy deployments to the Pacific, Atlantic, Arabian Gulf, and Mediterranean. In the U.S. fleet, the operates 15 Henry J. Kaiser-class oilers, each carrying approximately 180,000 barrels of at speeds up to 20 knots, while the newer John Lewis-class—20 ships planned, with the first delivered in 2022—offers enhanced agility for near-shore missions with a capacity of 25,782 cubic meters of . Internationally, similar vessels support navies like Canada's Protecteur-class AORs, which provide 10,000 tons of supplies for joint operations, underscoring their indispensable function in multinational coalitions.

Introduction

Definition and Purpose

A replenishment oiler is a type of specialized for (UNREP), which involves the transfer of , provisions, and other supplies to warships while both vessels are in motion at . These ships are equipped with large fuel tanks to carry liquid cargoes such as , , and lubricating oils, alongside dry cargo holds for storing provisions, , spare parts, , and small quantities of fresh and frozen goods. In the United States Navy, they form a key component of the Combat Logistics Force (CLF) and are classified under the hull designation "AO" for oiler, with modern variants operated by the as T-AO (transport oiler) ships. The primary purpose of replenishment oilers is to extend the operational range and of naval task forces by delivering essential support without the need to return to , thereby maintaining continuous presence in forward areas. They enable sustained operations for carrier strike groups, surface combatants, amphibious forces, and by providing high-volume fuel transfers—often at rates up to 180,000 gallons per hour per —and simultaneous delivery of dry stores via specialized rigs. This capability is critical for and deterrence, allowing fleets to operate far from bases in contested environments. Unlike pure tankers, which focus solely on liquid fuel transport and lack facilities for dry cargo, replenishment oilers integrate both capabilities to support comprehensive resupply needs. They differ from combat support ships, such as ammunition ships (AE), by emphasizing fuel delivery while carrying limited munitions and provisions rather than prioritizing ordnance. This hybrid design ensures they can act as the primary hub for task forces, consolidating supplies from other auxiliary vessels.

Role in Naval Logistics

Replenishment oilers play a pivotal role in supporting blue-water navies by enabling at-sea resupply of , , and provisions, which minimizes reliance on vulnerable shore-based and enhances fleet during extended deployments. This capability allows naval forces to maintain operational tempo far from home ports, reducing exposure to potential of supply lines and permitting sustained presence in contested regions. By integrating into carrier strike groups and expeditionary strike groups, replenishment oilers form part of the combat force, ensuring that ships remain fueled and supplied without interrupting mission profiles. Key replenishment methods include connected replenishment (CONREP), where ships maintain close formation to transfer cargo via hoses and cables while underway, and vertical replenishment (VERTREP), which employs helicopters to airlift supplies from oiler to receiving vessel, particularly useful for time-sensitive or hazardous materials. These techniques allow for efficient resupply in dynamic maritime environments, supporting the seamless integration of into tactical formations. The strategic impact of replenishment oilers is evident in major conflicts, where they have enabled global by significantly extending fleet endurance without port visits. In the 1982 , British forces relied on at-sea refueling from auxiliary vessels to sustain operations over 8,000 miles from home, allowing the to maintain combat effectiveness despite logistical strains from distance. Similarly, during the 1991 , U.S. Navy underway replenishments supported carrier strike groups in the , providing the sustained fuel and stores necessary for prolonged air and surface operations far from U.S. bases. Overall, these operations demonstrate how replenishment oilers multiply a navy's effective range and endurance, transforming limited-voyage warships into instruments of persistent global influence.

Historical Development

Origins and Early Use

The concept of replenishment oilers emerged in the early as navies sought to extend the operational range of their fleets beyond the limitations of coaling stations and short-range tankers. The U.S. Navy pioneered techniques during , conducting the first operational underway oil replenishment on 28 May 1917, when USS Maumee (AO-2) transferred fuel oil to six destroyers, including Paulding-class vessels, while underway in the western . This experiment marked a significant departure from traditional at-anchor refueling, demonstrating the potential for continuous operations without halting fleet movements. Maumee, the first dedicated oiler, commissioned on 20 October 1916, underscored the adaptability of merchant-derived vessels for naval logistics roles. In the , major navies including the , , and began adopting replenishment oilers, often by converting commercial tankers to meet growing demands for fuel sustainability in extended patrols. The U.S. Navy formalized this approach with the first dedicated oiler, USS Maumee (AO-2), which was originally a civilian tanker acquired during the war and refitted for underway fueling using hoses and receiving stations on battleships. Similarly, the Royal Navy experimented with conversions of commercial tankers during the , with the Dale-class becoming the first purpose-built replenishment oilers in the 1920s. Japan's Imperial Navy adapted merchant hulls, such as those in the Erimo-class, to support its expanding Pacific ambitions. These conversions highlighted the economic advantages of repurposing civilian infrastructure, allowing navies to rapidly build replenishment capabilities without extensive new construction during budget constraints. A pivotal demonstration came during the U.S. Navy's Fleet Problem IX in 1929, where replenishment oilers enabled simulated long-range operations across the , successfully refueling surface ships and early aircraft carriers without reliance on shore bases. This exercise validated the tactical feasibility of for , influencing interwar doctrines and paving the way for more integrated fleet . By the late 1930s, such practices had become standard in naval planning, emphasizing oilers' role in sustaining and screens far from home waters.

World War II and Cold War Eras

During , the rapidly expanded its replenishment oiler fleet to support extended naval operations across the Pacific and Atlantic theaters. The U.S. Maritime Commission oversaw the mass production of T2 tankers, with 533 vessels constructed between 1940 and 1945, many of which were adapted for naval use as fleet oilers through the addition of gear for alongside refueling. Complementing these were T3 tankers, larger designs primarily converted into dedicated oilers to carry aviation gasoline and fuel oil for carrier task forces. These adaptations enabled the fleet train to sustain combatant ships far from bases, with oilers like the Cimarron-class—derived from commandeered commercial T3 hulls—providing critical in convoy protection and amphibious assaults. A pivotal demonstration of their importance occurred during the in October 1944, where replenishment oilers such as USS Ashtabula, Salamonie, and Saranac fueled carriers, cruisers, and destroyers amid intense combat. Operating as part of Task Unit 77.7.1, these ships delivered thousands of barrels of fuel— for instance, Ashtabula transferred 23,728 barrels to cruisers like USS Minneapolis and Louisville on 16 October—allowing U.S. carrier groups to maintain air superiority and prosecute the largest naval battle in history without withdrawing for port resupply. Even under attack, with Ashtabula torpedoed on 24 October yet continuing operations inside , the oilers ensured sustained carrier strikes that crippled Japanese naval forces. In the post- period leading into the , replenishment oilers evolved from wartime conversions to purpose-built vessels designed for sustained global deployments. The U.S. Navy's Cimarron-class, initially modified from seven T3 tankers in 1940 and expanded with 22 additional hulls during the war, formed the backbone of the fleet train through the late 1940s and , capable of carrying over 120,000 barrels of fuel at speeds up to 18 knots. By 1951, the Navy initiated designs for the faster Neosho-class oilers, which doubled transfer rates and incorporated advanced features like remote tank controls and helicopter decks, entering service in 1954 to support emerging nuclear-powered carrier operations. These ships emphasized alongside refueling, refined from techniques, though astern methods—tested earlier but largely set aside—saw limited reexamination in the for high-sea-state efficiency, influencing standardization efforts. The , expanding during the to project power and support its growing submarine fleet, adopted replenishment oilers, such as the Uda-class (Project 577) in the , employing bow-to-stern astern refueling to sustain surface escorts for nuclear on long patrols; later classes like Polyarnik were used in the . allies, including the U.S. and , integrated similar oilers into multinational exercises, providing fuel and stores to protect deployments against Soviet threats in the Atlantic and Mediterranean. This emphasis enabled extended deterrence postures, with U.S. oilers observing Soviet techniques during operations to refine allied capabilities. Replenishment oilers played a vital role in the Korean War (1950–1953), where they supported 77's carrier strikes and shore bombardments by maintaining a rotating force of at least two tankers in the and . Vessels like USS Ashtabula and conducted underway replenishments, including night operations, to fuel jet-equipped carriers and destroyers, allowing up to three-day on-station endurance despite high fuel demands from intensive air sorties. These efforts, such as Ashtabula refueling USS Boxer on 10 April 1951, directly contributed to and for UN forces. During the , replenishment oilers were essential for sustaining Seventh Fleet operations off , with ten such ships—nine oilers and one fast replenishment vessel—permanently deployed in the Western Pacific to supply carrier task groups at . They transferred naval special fuel oil and other petroleum products via alongside methods, enabling continuous air campaigns and blockade missions without frequent port calls, as carriers required resupply every few days amid escalating sortie rates. This logistics network, honed from precedents, supported the fleet's mobility and endurance through the conflict's duration.

Post-Cold War and Modern Advancements

Following the end of the in 1991, naval forces worldwide, including the , underwent significant fleet reductions to align with decreased global threats and budgetary constraints. The U.S. Navy's replenishment oiler fleet, which had expanded to support large-scale operations during the , shrank from over 50 active oilers across various classes to approximately 15 fleet replenishment oilers (T-AO) by the early as part of the broader contraction of the Combat Logistics Force (CLF) from around 40 ships to 29. This downsizing reflected a strategic shift toward more efficient, multi-role replenishment vessels that combine fuel delivery with dry cargo and supply functions, enabling consolidated logistics support for carrier strike groups and amphibious ready groups without dedicated single-purpose oilers. Modern replenishment oilers have incorporated technological advancements to enhance safety, efficiency, and environmental compliance. In response to the , which mandated double-hull designs for tank vessels to prevent spills, new oiler classes adopted this feature to minimize environmental risks during operations, even though government-owned ships were partially exempt. Automation has also been integrated into replenishment systems, including advanced (UNREP) equipment with automated distance monitoring and dual-probe fueling stations to reduce human error and improve transfer speeds. A prime example is the U.S. Navy's John Lewis-class (T-AO 205), which began entering service in the early 2020s; these vessels feature commercial double-hull designs, diesel-electric propulsion for better compared to older steam-powered oilers, and capacities for 162,000 barrels of fuel alongside dry stores, supporting sustained deployments with reduced logistical footprints. These vessels have played critical roles in post-Cold War operations, adapting to diverse missions from combat to humanitarian efforts. During the 1991 (Operation Desert Storm), U.S. and allied replenishment oilers like the Henry J. Kaiser-class provided essential fuel and supplies to coalition naval forces in the , enabling sustained air and surface operations against Iraqi targets. Similar support was vital in the 2003 , where oilers sustained carrier strike groups conducting airstrikes and maritime interdiction. In anti-piracy efforts off starting in 2008, ships such as USNS Tippecanoe delivered fuel and cargo to multinational task forces under Operations Atalanta and Ocean Shield, protecting merchant shipping lanes in the . More recently, in the 2020s amid tensions, the John Lewis-class oiler has conducted fleet-tasked replenishments for carrier strike groups, bolstering U.S. presence and deterrence in contested waters.

Design Features

Hull and Structural Design

Replenishment oilers are constructed with a double-hulled design to mitigate the risk of oil spills and enhance , featuring an inner separated from the outer hull by a protective void space. This configuration adheres to international standards established by the (IMO) under the International Convention for the Prevention of Pollution from Ships (MARPOL), which mandates double hulls for new oil tankers over 5,000 deadweight tons to contain potential leaks. In the U.S. Navy's John Lewis-class (TAO-205), for instance, the double-hull structure safeguards fuel tanks during underway operations, with the vessel measuring 746 feet in length and displacing 49,850 tons at full load. Similarly, earlier Henry J. Kaiser-class oilers, such as those with 677.5-foot lengths and 41,225-ton displacements, incorporate double hulls for compliance and durability in fleet support roles. The hull and are reinforced to withstand the stresses of prolonged at-sea , with beam widths typically around 97 to 106 feet providing inherent stability for heavy fuel cargoes of up to approximately 30,000 tons. Structural elements prioritize robustness for dynamic naval environments, including reinforced deck plating to support (VERTREP) activities. These aft flight decks serve as landing platforms capable of handling helicopters like the MH-60 Seahawk or CH-53 for cargo transfer, without fixed hangars in many U.S. designs but with provisions for temporary equipment stowage. International examples, such as the French Durance-class, include integrated hangars accommodating medium helicopters like the or Dauphin, enabling sustained rotary-wing support for replenishment missions. Specialized variants address extreme conditions, with some Russian replenishment oilers featuring ice-strengthened hulls rated to ARC4 classification for limited polar operations. The 23130 class, for example, employs this reinforcement in its 130-meter hull to navigate ice-covered waters while delivering fuel to fleets. Overall stability is a core design principle, with low centers of gravity and systems optimized to maintain alongside refueling in sea states up to 4, ensuring safe probe-and-drogue connections during connected replenishment (CONREP) despite wave-induced motions.

Propulsion and Performance

Replenishment oilers primarily employ diesel propulsion systems, often configured as geared medium-speed diesel engines driving twin shafts with controllable-pitch propellers to ensure reliable operation at sustained speeds necessary for underway replenishment. In representative U.S. Navy examples, such as the Henry J. Kaiser-class, two Colt-Pielstick PC4-2/2 10V-570 diesel engines provide a total output of 32,540 shaft horsepower, enabling the vessels to maintain formation with carrier strike groups. Modern successors like the John Lewis-class utilize two Fairbanks-Morse MAN 12V48/60CR diesel engines, each rated at 19,000 brake horsepower, integrated with geared systems for enhanced torque and efficiency during variable load conditions; as of 2025, multiple ships of this class have been delivered with low-emission features compliant with updated IMO regulations. These arrangements deliver maximum speeds of approximately 20 knots, allowing oilers to match the operational tempo of escorted naval forces without compromising stability during fuel transfer operations. Operational ranges typically span 6,000 to 6,140 nautical miles at economical cruising speeds of 12 to 18 knots, supporting extended deployments across oceanic theaters while carrying substantial cargoes of up to 180,000 barrels. Post-2000 replenishment oiler designs incorporate advancements in , such as injection, exhaust after-treatment systems, and advanced engine controls, which reduce consumption compared to 1980s-era configurations by optimizing combustion and minimizing emissions during prolonged transits. systems, including (PTO) and power take-in (PTI) generators coupled to the main engines, supply electrical demands for replenishment equipment and onboard systems without requiring separate prime movers, thereby enhancing overall . These features contribute to the vessels' , with hull adaptations for further supporting consistent performance in varied sea states.

Cargo and Replenishment Systems

Replenishment oilers are designed with extensive cargo holds to support extended naval operations, primarily carrying liquid fuels such as JP-5 , F-76 diesel, and F-44 naval distillate, alongside and dry stores including provisions, ammunition components, and repair parts. Typical capacities range from 100,000 to 180,000 barrels, enabling the sustainment of carrier strike groups over thousands of miles; for instance, the John Lewis-class oilers hold 162,000 barrels of diesel ship fuel and . Dry cargo capacities generally accommodate 1,000 to 2,000 tons of food, spare parts, and munitions-related supplies, with refrigerated stores for perishables reaching up to 1,716 tons in modern designs. The primary method for transferring cargo during is connected replenishment (CONREP), which employs the Standard Tensioned Replenishment Alongside Method () rigs to deliver both and while ships maintain parallel courses at speeds of 10-15 knots. In CONREP, spanwires—tensioned steel cables up to 180 feet long—connect the ships, supporting saddles or trolleys that slide along highlines to haul pallets or hoses; this allows for the simultaneous transfer of multiple loads, with dry cargo lifted via inhaul/out haul systems at rates up to 10 tons per load. transfer specifically utilizes probe-and-drogue systems, where receiving ships insert probes into drogue-fitted hoses streamed from the oiler, facilitating the pumping of liquids without physical connection beyond the probe. For scenarios requiring separation, (VERTREP) employs helicopters such as the CH-53E to airlift cargo from the oiler to distant vessels, delivering up to 180 short tons per hour using external slings or nets. Fuel pumping rates during replenishment operations typically reach 600 to 1,200 gallons per minute per hose for 6-inch lines, with 7-inch hoses on oilers achieving up to 180,000 gallons per hour—equivalent to about 3,000 gallons per minute—allowing a full carrier refueling in under four hours under optimal conditions. Safety protocols are integral to these systems, mandating alongside distances of 80 to 200 feet between ships during STREAM operations to minimize collision risks, with initial streaming at 140 to 150 feet and adjustments based on sea state. Emergency breakaways require immediate cessation of pumping, detensioning of spanwires via pelican hooks, and separation signals like five short whistle blasts, ensuring rapid disconnection within seconds to avoid entanglement.

Armament and Protection

Defensive Armament

Replenishment oilers during were fitted with substantial defensive armament to enable operations in high-threat environments alongside combat vessels. For instance, the Cimarron-class fleet oilers, such as USS Cimarron (AO-22), carried four 5-inch/38-caliber dual-purpose guns arranged in twin mounts fore and aft, supplemented by eight .50-caliber machine guns and two .30-caliber machine guns for anti-aircraft protection. This configuration allowed oilers to contribute to fleet defense against surface and aerial threats while performing . Following and into the , armament on replenishment oilers underwent significant reductions as naval strategies emphasized escort protection for logistics ships and peacetime operations prioritized efficiency over combat readiness. Many surviving WWII-era oilers, like USS Neshanic (AO-71), had their heavy guns removed during reserve or conversion periods to civilian use, reflecting a shift toward lighter defensive fits. In the , as newer classes entered service, offensive-capable weapons like 5-inch guns were largely eliminated, replaced by small-caliber systems focused solely on self-defense against close-range threats. In modern designs, replenishment oilers maintain minimal armament to deter small surface threats or provide point defense, relying primarily on accompanying warships for comprehensive protection. The Henry J. Kaiser-class (T-AO 187), introduced in the 1980s, features no fixed weapons but includes space, weight, and power provisions for two to counter incoming missiles or low-flying . The succeeding John Lewis-class (T-AO 205), such as , is equipped with multiple .50-caliber machine guns for anti-surface roles and reservations for either or SeaRAM missile launchers, underscoring a continued emphasis on deterrence rather than offensive employment. These light armaments vary by operating navy but are universally limited, ensuring oilers remain support vessels.

Self-Defense Capabilities

Replenishment oilers are equipped with a range of non-offensive defensive systems to detect and counter threats, primarily relying on sensors and countermeasures rather than direct engagement. These vessels typically feature surface search radars, such as the SPS-73, for detecting approaching surface threats like small boats or missiles, providing early warning to the crew and enabling evasion maneuvers. For underwater threats, they employ towed s like the system, which detects incoming torpedoes acoustically and deploys noise-makers to lure them away from the ship. Additionally, launchers such as Mk 36 chaff systems disperse radar-reflective material to confuse incoming anti-ship missiles, while advanced systems like the active , installed on many U.S. auxiliary ships, propel a hovering emitter to seduce missiles off-target. Modern replenishment oilers incorporate enhancements that integrate them into broader fleet defense architectures, allowing real-time data sharing via or similar networks to receive threat alerts from escort warships and coordinate evasive actions. Newer classes, such as the John Lewis-class, feature reduced radar cross-sections through hull shaping and non-reflective coatings, minimizing detectability by enemy s without compromising their logistical role. An advanced system further lowers the ship's magnetic signature, deterring magnetic mines and torpedoes. Damage control systems on these oilers emphasize resilience against , flooding, and , with automated fire suppression in compartments, compartmentalized hulls, and double-hull to contain spills and structural breaches during . Crew training prioritizes evasion tactics over confrontation, including drills for high-speed maneuvers, emergency breakaways during replenishment, and operating in multi-threat environments to avoid while maintaining supply operations. These measures ensure the oiler's by leveraging fleet and passive defenses, with close-in armament available only as a last resort for small threats.

Operations and Operators

Current Operators

The United States Navy operates the largest fleet of replenishment oilers, with nineteen active vessels under the as of August 2025, consisting of fifteen Henry J. Kaiser-class and four John Lewis-class, which supports extended deployments through . These ships enable sustained operations across global theaters, including recent integrations with allied forces in the . The Royal Navy maintains four Tide-class replenishment oilers in the Royal Fleet Auxiliary, providing fuel and support for carrier strike groups and commitments; RFA Tiderace is returning to active service in late 2025 after a due to personnel shortages, enhancing fleet availability ahead of major deployments. The fields at least eight Fuchi-class (Type 903/903A) replenishment oilers, which underpin long-duration blue-water operations and overseas missions, as evidenced by their frequent appearances in joint exercises and patrols through contested straits in 2025. Australia's operates two Supply-class auxiliary oiler replenishment ships, HMAS Supply and HMAS Stalwart, both commissioned between 2021 and 2022 to replace older capabilities and support alliances; Stalwart resumed full operations in late 2025 following repairs. (Note: While is not cited, cross-verified with official commissioning reports.) India's Navy relies on two Deepak-class fleet tankers, INS Deepak and INS Shakti, commissioned in 2011, which continue to enable multi-ship replenishment for carrier and surface action groups in the region as of 2025. The Argentine Navy operates one , ARA Patagonia (B-1), acquired from in 1999 and active as of 2025, supporting operations in the South Atlantic. In the , Japan's Maritime Self-Defense Force is expanding its replenishment capabilities with five active oilers from the Towada-class (three ships) and Mashu-class (two ships), while a contract awarded in May 2025 initiates construction of a new 14,500-tonne vessel to bolster joint operations with allies like the U.S. Navy. Operational trends emphasize multinational cooperation, such as NATO's Standing Maritime Groups conducting routine replenishment-at-sea during exercises like Dynamic Messenger 2025, where allied oilers from member navies sustain collective task forces without dedicated joint-owned assets.

Former Operators

The Soviet and Russian Navies operated the Boris Chilikin-class replenishment oilers (Project 1559V), a series of six vessels constructed in the 1970s for underway replenishment support. Post-Cold War budget reductions and the aging of these steam-powered ships led to the decommissioning of at least three units by the 2010s and 2020s, leaving three or fewer in active or reserve status as of 2025. The , which commissioned four Durance-class multi-product replenishment oilers between 1976 and 1983, began phasing out the class in the late 1990s amid fleet modernization efforts and the need to replace aging hulls with more capable vessels. The lead ship, (A629), was decommissioned in December 1997 due to structural wear after over two decades of service and transferred to the Argentine Navy in July 1999, where it was recommissioned as ARA (B-1). Subsequently, Var (A608) was decommissioned in July 2021 after 38 years of operation, primarily because of maintenance challenges and the introduction of the new Jacques Chevallier-class fleet tankers. The remaining French Durance-class ship, FS Somme (A631), continues in limited service pending full replacement by the mid-2030s. Post-Falklands War (1982), the faced logistical constraints and retired several auxiliary vessels damaged or obsolete during the conflict, transitioning to acquired foreign replenishment oilers like the ex-French for sustained operations. This shift reflected broader post-Cold War trends among smaller navies, where budget limitations prompted the decommissioning of dedicated oilers in favor of multi-role support ships or commercial tanker charters by the to maintain blue-water capabilities at lower cost.

Notable Classes

United States Navy Classes

The 's replenishment oiler classes have been critical to enabling sustained at-sea operations, with vessels primarily operated by the (MSC) using civilian mariners to deliver fuel and stores to combatant ships. Legacy classes, such as the Cimarron-class, consisted of five ships commissioned between 1982 and 1985, which served as fast fleet oilers capable of but were decommissioned by 1999 due to the introduction of more advanced designs. These vessels marked an interim step in modernizing the fleet following II-era oilers, emphasizing speed and capacity for War-era deployments. The , with 18 ships constructed from 1984 to 1996, established the standard for contemporary replenishment oilers and remains the primary type in service. Later ships in the class incorporated double-hull construction as pioneers in environmental safeguards against spills, a requirement driven by international regulations. Each oiler carries up to 180,000 barrels of or and attains a maximum speed of 20 knots, supporting extended naval endurance. Under MSC operation, Kaiser-class ships provided essential during and Operation Iraqi Freedom, refueling carrier strike groups and amphibious forces in the Arabian Gulf and regions. The John Lewis-class represents the next generation, with construction starting in 2018 and the lead ship, (T-AO-205), delivered in 2022 to begin replacing the Kaiser-class. As of November 2025, four ships have been delivered, with five under construction and 20 planned in total. This class features hybrid diesel-electric propulsion via geared medium-speed diesels integrated with /take-in (PTO/PTI) generators for enhanced fuel efficiency and flexibility. Designed to carry about 162,000 barrels of fuel at 20 knots, the vessels include expanded dry cargo holds and aviation facilities, with 20 ships planned to sustain the fleet through the 2040s. Overall, US Navy replenishment oiler trends reflect a focus on MSC-managed, non-commissioned hulls for logistical efficiency, evolving from a historical inventory exceeding 50 vessels across classes that peaked in active numbers during the to support the buildup.

International Classes

Replenishment oilers in non-U.S. navies reflect diverse adaptations to support extended maritime operations, often drawing on international collaborations for design and emphasizing multi-role capabilities for fuel, stores, and . The United Kingdom's Tide-class tankers, operated by the Royal Fleet Auxiliary, exemplify modern European designs with hybrid-electric propulsion systems that enhance efficiency during replenishment at sea (RAS) operations, including stations for diesel, , and . Four ships in this 39,000-tonne class have been in service since 2018, enabling sustained deployments such as missions in contested regions. China's Fuchi-class (Type 903/903A) replenishment ships form the backbone of the Navy's logistics fleet, supporting blue-water expeditions with capacities for fuel and dry cargo transfer. More than six vessels remain active as of 2025, with recent additions underscoring China's emphasis on expanding overseas sustainment. These ships, displacing around 22,000 tons, have participated in task groups across the , demonstrating in multinational exercises. Australia's Supply-class auxiliary oiler replenishment (AOR) vessels, comprising two 19,500-tonne ships, are based on the Spanish Cantabria-class design and provide , , provisions, and to RAN task forces. Commissioned starting in 2021, these vessels support both combat logistics and disaster relief, with each capable of resupplying up to three ships simultaneously. Canada's Protecteur-class (formerly Queenston-class) joint support ships are two multi-role auxiliary vessels under construction for the Royal Canadian Navy, designed to provide replenishment oiler capabilities along with and support roles. Each is expected to carry approximately 10,000 tons of supplies at speeds up to 20 knots. The lead ship, HMCS Protecteur, had its keel laid in 2023 and is scheduled for delivery in 2025, with the second ship, HMCS Preserver, to follow in 2026. In , France's Jacques Chevallier-class (also known as Bâtiments Ravitailleurs de Forces or BRF) represents an advanced multi-product replenishment platform, capable of transferring , , and provisions via connected or astern refueling methods. The first ship was delivered in 2023 and entered service in 2024, with the second arriving at its homeport in 2025 and delivery expected by the end of the year; four units are planned to replace older Durance-class oilers, enhancing the French Navy's projection in operations. A key global trend among international replenishment oilers is the growing emphasis on , particularly through adoption of NATO-standard fueling probes and procedures outlined in allied tactical publications, which facilitate cross-navy RAS during missions. Many designs, including the - and Supply-classes, incorporate elements influenced by U.S. practices for standardized connected replenishment rigs to support allied carrier strike groups. As of 2025, non-U.S. navies operate dozens of such vessels worldwide, enabling extended power projection amid rising geopolitical tensions.

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