• KC-10A Extenders served as aerial refueling tankers in the US Air Force from 1981 to 2024.
• The first KC-10A Extender ever built is on display at the Air Mobility Command Museum in Delaware.
• Visitors can get a rare glimpse into the aircraft's refueling operator station.

Military aircraft don't have time to stop and refuel during sensitive, time-critical missions. That's where aerial refueling tankers come in.

With their ability to transfer up to 56,154 gallons of fuel to planes in midair, KC-10A Extenders refueled bombers, fighter jets, cargo planes, and other aircraft in the US Air Force for over 40 years, increasing their range and mobility.

The Air Mobility Command Museum on Dover Air Force Base in Delaware offers visitors the chance to see inside the first KC-10A Extender ever built.

Business Insider visited the museum in May to tour the KC-10A Extender and get a rare glimpse into its refueling operator station. Take a look.

KC-10 Extenders were primarily built as aerial refueling aircraft, but they also carried cargo and conducted aeromedical evacuations.

KC-10s entered service in the Air Force in 1981. They provided in-flight refueling in combat operations during the Gulf War and the Iraq War, and supported aircraft during Operation Allied Force in 1999.

They also helped carry out the largest non-combatant evacuation operation in US history during the Taliban offensive in Afghanistan in 2021, when 40% of the KC-10 fleet was deployed to evacuate over 3,000 people and refuel other aircraft, according to the Air Force.

The KC-10 was a military version of the DC-10 airliner built by McDonnell Douglas, which merged with Boeing in the late 1990s. The DC-10 has similarly been retired by commercial airlines.

The last KC-10 was retired in 2024.

While KC-10 refueling jets have been retired, the Air Force still uses KC-135 Stratotankers, which entered service in 1957, and introduced the KC-46A Pegasus in 2019 as part of efforts to upgrade its aging tankers.

The US Air Force plans to buy over 260 KC-46s from Boeing, with each costing about $200 million. The Stratotankers and Pegasus aircraft have fallen short of readiness standards in recent years.

With a capacity of over 356,000 pounds of fuel, KC-10s could carry nearly twice as much fuel as the KC-135 Stratotanker. However, KC-10s were phased out, while the Air Force still uses KC-135s.

So, why didn't KC-10s remain in service as long?

"You can ask 10 different people and get 20 different answers to that," Michael Hurlburt, operations manager at the Air Mobility Command Museum and an Air Force veteran, told Business Insider.

Hurlburt thinks the KC-10's third engine was partially to blame, since its position above the fuselage on the vertical stabilizer required special scaffolding platforms for inspection before every flight, which he called a "maintenance nightmare."

The KC-10A Extender on display at the Air Mobility Command Museum on Dover Air Force Base was the first one ever built.

The museum's KC-10A Extender was built as a prototype for a larger, longer-range alternative to KC-135 Stratotankers. It clocked over 32,560 flying hours before it was retired to the Air Mobility Command Museum in 2022.

The KC-10A Extender measures 181 feet and 7 inches long with a wingspan of 165 feet and 4 ½ inches.

The aircraft is open for guided tours. Museum admission is free.

A model of the KC-10A Extender helps orient visitors when they step inside the aircraft.

The flight deck and passenger compartment are located up front. The cargo bay takes up most of the remaining space, with the refueling operator station at the back of the plane.

The KC-10A Extender could carry up to 75 passengers.

Seats in the passenger compartment resembled those on regular commercial airlines.

The crew consisted of a pilot, co-pilot, flight engineer, and boom operator.

For cargo transport missions, a loadmaster would join the crew. For aeromedical evacuations, two flight nurses and three medical technicians were added.

The cargo bay could hold 170,000 pounds of cargo.

On refueling missions, extra fuel tanks were also kept in the cargo bay, totaling up to 356,000 pounds of transferable fuel.

On display in the cargo bay was a wing air-refueling pod, or WARP.

WARPs can be mounted under a tanker's wings to provide additional refueling points. On the KC-46, the successor to the KC-10, WARPs are in testing to enable the Pegasus to simultaneously refuel two aircraft.

The refueling operator station was located down a narrow set of stairs at the rear of the aircraft.

To receive fuel in-flight, other aircraft positioned themselves behind and lower than the KC-10.

The boom operator used a joystick to connect the boom — the extended gas pump — to other planes to transfer fuel during in-flight refueling.

In KC-10s, boom operators sat upright. In KC-135s, boom operators lie on their stomachs to operate the controls.

The boom operator's job is to guide a rigid pipe into a receptacle on the receiving aircraft.

Once the boom is connected, the operator turns on the pumps to begin transferring fuel at a maximum rate of 1,100 gallons per minute. An F-15 Eagle, for example, can carry over 5,000 gallons of jet fuel.

In-flight refueling is a dangerous operation requiring tankers and the planes they refuel to fly within 8 to 12 feet of each other at hundreds of miles per hour.

"You're close enough that you can wave and say hi to the other pilot in the other airplane," Hurlburt said.

Mistakes can be catastrophic. In July 2025, a KC-46A Pegasus refueling aircraft's boom got stuck in the receptacle of an F-22A Raptor and broke off, causing nearly $10 million in damage. In March, a KC-135 tanker crashed in Iraq, killing all six crew members.

Museum visitors can take a closer look at the boom outside the aircraft.

The boom is labeled with signage from the 305th Air Mobility Wing, located at Joint Base McGuire-Dix-Lakehurst in New Jersey, where this KC-10A Extender served from 1995 until its retirement in 2022.

Hurlburt described the boom operator's window as a "very rare view."

"Very few airplanes have something like this, and very few people get to see areas like this," he said. "We're pretty proud of being able to show this off."

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