The KC-135 Stratotanker, described by the US Air Force as a gas station in the sky, has provided transport and extended the range and endurance of US tactical fighters and bombers for decades.

The aerial refueling tanker has been a mainstay of the US Air Force's tanker fleet for more than 60 years and continues to remain a key aircraft today.

The KC-135 enhances the Air Force's capability to accomplish its primary mission of global reach, according to the Air Force. It also provides aerial refueling support to Navy, Marine Corps and allied nation aircraft.

The Stratotanker can pump 200,000 pounds (90,700kg) of fuel through a flying boom, which is controlled by a crew member during in-flight refueling, according to the Air Force.

Above the refueling system is a cargo deck that can carry passengers and cargo. Depending on the fuel storage configuration, the KC-135 workhorse can haul up to 83,000 pounds (37,600kg) of cargo.

Four turbofans power the KC-135 to takeoff, carrying gross weights topping 322,500 pounds (146,200kg).

The US Air Force purchased its first 29 Stratotankers in 1954. Hundreds more followed, and the last KC-135 was delivered to the service in 1965.

More than 800 of them have been built since the 1950s, making the KC-135 Stratotanker the most experienced refueler in the world.

A history of service

The US Air Force maintains 377 KC-135 aircraft, according to Flight Global's 2024 World Air Forces directory. Many fly with the Air Force Reserve and Air National Guard, which fly Stratotankers in support of Air Mobility Command's mission.

The Air Force's current inventory are more than 50 years old and have been retrofitted several times with new engines, avionics and structural upgrades.

The life-cycle upgrades expand capabilities and improve reliability for the workhorse aircraft. The upgrades include improved communications, navigation, autopilot and surveillance equipment to meet future civil air traffic control needs.

Through the years, variants of the KC-135 have been altered to do other jobs, including reconnaissance, transport and flying of other command post missions.

For example, the US Air Force and Royal Air Force use RC-135s for special reconnaissance. Meanwhile, US Air Force Materiel Command's NKC-135As are flown in test programs.

The KC-135 has also worked for medical transport. It can transport patients who are ambulatory or on stretchers using patient support pallets during aeromedical evacuations.

The long-lasting aircraft have exceeded expectations.

The Air Force plans to retain the fleet 10 years beyond its planned service life, keeping some jets in service to at least 2050.

Worldwide refueling

This aerial juggernaut has been in service around the world.

The Turkish Air Force had seven KC-135R Stratotanker aircraft upgraded in the last five years with new flight decks.

The Block 45 upgrade remodeled the inside of the flight deck with new displays, computer module updates, autopilot and digital flight director. The upgrades make it easier for pilots to operate the aircraft, note any malfunctions and sustain aircraft over the long run, according to the Air Force's Legacy Tanker Division, which oversees the upgrades.

The US Air Force has also made the Block 45 upgrade to its fleet. Prior to the process, the analog autopilot on the aircraft averaged 500 flight hours between failures. After the upgrade, they averaged 49,000 flight hours between failures, according to a 2021 assessment from the Air Force.

Until recently, the French Air and Space Force and the Singaporean Air Force also used C-135s.

The French Air and Space Force retired the last Boeing C-135FR from service in December. Until that point, it had used the C-135 since the 1960s for strategic readiness, long-distance logistical transport and refueling of aircraft.

The aircraft were part of French Air and Space Force regular missions to practice all phases for nuclear deterrence, which included a long high-altitude flight with inflight refueling.

In Singapore, the KC-135R Stratotanker served from 2000 to 2019. One of the longest missions it flew was a redeployment from New Mexico to Singapore in 2000. The journey took six days to complete, totaling 22 hours of flying.

The aircraft's international presence underscores its reputation for reliability and performance, making it a preferred choice for air forces across the globe.