“Ten (fifteen, twenty…) U.S. Air Force aerial refueling aircraft have departed air bases in the continental United States and redeployed to Spain, the United Kingdom, or Guam.” Reports of this kind usually indicate that Washington is preparing for another military operation somewhere far from its own territory.
Even before bombers and fighters begin their missions, and while airborne troops are still preparing to deploy to staging airfields, the tanker aircraft are already positioned along the planned flight routes of combat aviation. The large fleet of aircraft in this category is one of the key tools used by the United States for global power projection. The deployment of tanker aircraft also preceded the current conflict with Iran.
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How It All Began
The idea of extending an aircraft’s flight time through aerial refueling was first implemented more than a century ago in the United States. One of the pioneers behind this concept was Russian émigré and World War I military pilot Alexander Prokofiev-Seversky. The aviation company he later founded eventually became widely known as Republic Aviation Corporation.
His proposed concept was extremely simple. A tanker aircraft flying slightly ahead and above the receiving aircraft would release a long hose. A crew member aboard the receiving aircraft then had to manually catch the hose and insert it into the fuel tank opening, after which fuel was pumped using a hand pump.
This method was tested in practice on June 25, 1923, using two single-engine Airco DH-4B biplanes operated by the United States Army Air Service. Later that same year, similar aerial refueling experiments were conducted in United Kingdom and France.
For the next two decades, aerial refueling remained largely a demonstration stunt and a tool for setting endurance records rather than a practical operational capability. Notably, the Fédération Aéronautique Internationale (FAI) stopped registering flight endurance records achieved with aerial refueling after 1959.
That year, pilots Robert Timm and John Cook managed to keep a single-engine Cessna 172 in the air for 64 days, 22 hours, and 19 minutes. The reason for discontinuing such records was straightforward: flights of such extreme duration pushed pilots to dangerous levels of exhaustion, creating a high risk of accidents.
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British Priority
In 1935, British pilot and inventor Alan Cobham demonstrated an aerial refueling system that eliminated the need for the manual “catch the hose” procedure. In this system, the receiving aircraft deployed a steel cable behind it. This cable was caught by a hook attached to another cable released from the tanker aircraft. The cable was then reeled back into the tanker, where the receiving aircraft’s cable was connected to the refueling hose. The receiving aircraft subsequently reeled in its cable, drawing the hose toward itself. Once positioned high enough above the receiving aircraft, fuel could flow under gravity.
In 1934, Cobham founded the company Flight Refuelling Ltd (FRL). By 1939, its looped refueling system was used to refuel large flying boats such as the Short Empire during regular transatlantic flights. Tanker duties were performed by Handley Page Harrow aircraft. The outbreak of World War II brought these operations to an end.
Toward the end of the war, as the United Kingdom prepared to deploy its bomber formation known as Tiger Force to the Far East, planners expected Avro Lancaster and Avro Lincoln bombers to receive fuel in flight from converted tanker aircraft based on the Handley Page Halifax, equipped with FRL systems. This would have allowed British aircraft to strike targets in the Japanese home islands despite their shorter range compared with American Boeing B-29 Superfortress bombers. However, the war ended before these plans were implemented.
After the war, the United States Air Force acquired several FRL systems and installed them on Boeing B-29 Superfortress bombers converted into tanker aircraft. These were used to refuel specially modified B-29s and later the Boeing B-50 Superfortress. The main modification introduced by the United States was the addition of an automatic coupling mechanism for the refueling nozzle. This allowed aerial refueling at higher altitudes and eliminated the need to descend and depressurize the aircraft so a crew member could perform the connection manually.
This refueling system was used by the Boeing B-50 Superfortress bomber named Lucky Lady II during its famous first nonstop circumnavigation of the globe in 1949. From February 26 to March 3, the aircraft completed a flight around the world without landing in 94 hours and 1 minute. This achievement was made possible by four aerial refuelings carried out by four pairs of Boeing KB-29M tanker aircraft.
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American Technologies
In January 1948, Carl Spaatz, the first Chief of Staff of the newly established United States Air Force, declared aerial refueling one of the service’s key development priorities. The advantages were clear: it significantly extended the operational range of combat aircraft, enabled rapid redeployment to distant theaters of operation, and reduced the need for numerous overseas air bases. By June 30, 1948, the U.S. Air Force had already formed its first two tanker squadrons.
Aerial refueling was first used in combat during the Korean War (1950–1953). Republic F-84 Thunderjet fighter-bombers conducted missions from airfields in Japan, while refueling was performed by modified Boeing B-29 Superfortress aircraft. These operations used the “probe-and-drogue” refueling method, which was simpler and more practical than the earlier system developed by Flight Refuelling Ltd.
In the following years, aerial refueling became widely used in tactical aviation – for example, during exercises involving the transfer of American aircraft to Europe. However, the primary mission remained the refueling of strategic bombers carrying nuclear weapons. Organizationally, tanker units were incorporated into the Strategic Air Command.
Despite its convenience, the probe-and-drogue system had one limitation: a relatively low fuel transfer rate. In the late 1940s, Curtis LeMay, commander of Strategic Air Command, tasked Boeing with developing a refueling system capable of transferring fuel at a much higher rate. The result was the rigid telescopic boom system, known as the “flying boom,” which eventually became the standard refueling method for the U.S. Air Force.
There are a few exceptions. The probe-and-drogue system is still used for refueling search-and-rescue helicopters and remains the standard method in United States Navy aviation. The specifics of aerial refueling in naval aviation, however, are a topic deserving separate discussion.
American Scale
The first tanker aircraft equipped with the flying boom system was the Boeing B-29 Superfortress. Between 1950 and 1951, 116 of these bombers were converted into KB-29P tanker aircraft.
In 1957, production began on the world’s first mass-produced aerial refueling aircraft – the Boeing KC-97 Stratofreighter, which was developed on the basis of the strategic transport aircraft Boeing C-97 Stratofreighter. By 1956, as many as 811 of these aircraft had been built. Initially, the KC-97’s primary mission was to refuel the medium strategic bombers Boeing B-47 Stratojet. Each wing of 45 B-47s was assigned 20 KC-97 tankers. And there were no fewer than thirty-one such wings.
However, the career of the B-47 proved relatively short – the aircraft were retired by 1966. The KC-97, meanwhile, continued serving in the regular United States Air Force until 1973, and in the United States Air National Guard for another five years beyond that.
The piston-powered Boeing KC-97 Stratofreighter was not particularly well suited for refueling jet combat aircraft with high cruising speeds. As a result, in 1957 the United States Air Force began receiving jet-powered tanker aircraft – the Boeing KC-135 Stratotanker. This elegant four-engine aircraft with swept wings shared common roots with the passenger airliner Boeing 707. By 1965, a total of 803 aircraft had been produced, some of which were later converted for other missions. At the height of the Cold War, the U.S. Air Force had more than six hundred KC-135 tankers in service.
The end of the Cold War led to reductions and organizational restructuring. In 1992, all tanker units were transferred from the Strategic Air Command to the Air Mobility Command. By 2024, 376 KC-135 aircraft remained in service (151 in the regular Air Force, 62 in the Air Force Reserve, and 163 in the United States Air National Guard). All of them have undergone multiple modernization programs over the years. Interestingly, one KC-135 built in 1957 is still serving with the 161st Air Refueling Wing of the Arizona Air National Guard – meaning the aircraft is now nearly 70 years old. Even the newest KC-135s are already 61 years old.
Between 1981 and 1987, the United States Air Force received 60 tanker-transport aircraft – the McDonnell Douglas KC-10 Extender, developed on the basis of the three-engine passenger airliner McDonnell Douglas DC-10. A distinctive feature of the Extender was the use of two fuel transfer systems – the flying boom and the probe-and-drogue (“hose-and-drogue”). This allowed the KC-10 to refuel aircraft operated by the United States Navy and the United States Marine Corps. In addition, the KC-10 could also serve as a transport aircraft, carrying up to 77 tons of cargo.
Despite their relatively young age, all KC-10 aircraft were retired between 2020 and 2024. The main reason was the effort to standardize the U.S. Air Force tanker fleet following the introduction of the new Boeing KC-46 Pegasus.
The Boeing KC-46 Pegasus, developed on the basis of the twin-engine passenger airliner Boeing 767, was selected by the United States Air Force through the competitive KC-X program. Not without controversy – which deserves a separate discussion – it won over Airbus’s proposal, the KC-45, based on the Airbus A330. Currently, 179 KC-46 aircraft have been ordered. Between 2019 and the beginning of 2026, the Air Force received 110 of them, with the remaining units expected to be delivered in the coming years.
The latest KC-46 aircraft, along with older KC-135s, are participating in Operation Epic Fury against Iran. However, the military has raised significant concerns regarding the KC-46’s quality and reliability. It is possible that procurement of these aircraft will be limited to the initial order, with an additional competition planned to replace the remaining KC-135s. Consequently, the KC-135 fleet is likely to remain in service at least until the middle of the next decade.
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