22,000 FEET ABOVE THE NEW JERSEY COAST — "Thirty feet, nice and slow. … Twenty feet. … Fifteen, nice and slow. Ten feet. Five feet. And contact, boom interphone."

Senior Master Sgt. Jimmie Rush Jr., an Air Reserve Technician and boom instructor with the 514th Air Mobility Wing at Joint Base McGuire-Dix-Lakehurst, moves the boom from his KC-10 into position to refuel another tanker, giving his pilot constant updates as two massive jets inch toward an aerial hook-up.

Every 15 minutes, somewhere in the world, an Air force tanker like Rush's KC-10 takes to the skies.

The flying fuel tanks spend their days — and nights and weekends — standing ready to provide badly needed fuel to most any friendly who asks.

They even top off Air Force One.

But the tankers are among the oldest airplanes in the Air Force. The average age of a KC-135 is 55 years old; the "newer" KC-10s average 30 years old, officials said.

They are operated by Air Mobility Command, U.S. Air Forces in Europe, Pacific Air Forces, Air Force Reserve Command and the Air National Guard.

Despite their advanced age, the tankers can't afford to slow down. There is always an airplane running out of gas, looking for a hook-up with a tanker, often in the middle of a mission.

The statistics bear that out: Air Mobility Command, Air National Guard and Air Force Reserve Command tankers flew 33,645 air refueling sorties in fiscal 2015, filling up aircraft 132,341 times and moving about 209 million gallons of fuel, according to Air Mobility Command.

Fighters, bombers and cargo aircraft cannot do their jobs without the ability to refuel midair. In October, a CBS News' "60 Minutes" story about the air war against the Islamic State group noted that a B-1 bomber carrying more than 17tons of bombs needed to refuel twice while en route from Qatar to Iraq.

With the KC-46 still in development, the Air Force's existing tanker fleet will continue to be a workhorse, making sure that combat and mobility aircraft get where they need to go.

"When all is said and done, our ability to project power — whether it's on the ground, whether it's in the air — all basically relies on aerial refueling," said Rep. Adam Kinzinger, R-Ill., who flew KC-135s from 2005 to 2008. "You can't get Marines in theater unless you stop everywhere without aerial refueling. You can't get bombs on target. It's the key backbone of being able to project power."

Kinzinger is a major in the Wisconsin Air National Guard, and he now flies the RC-26B. When he flew KC-135s, the tankers in his unit were in tiptop shape, but Kinzinger could tell that he was flying an old plane, he told Air Force Times in a Nov. 5 interview.

"It's updated with the new engines, the new avionics, so I didn't necessarily sense as I was flying that this was an old thing about to break apart, but I definitely knew that you had to be wary of the age of it," he said.

The reason the KC-135s keep flying is the aircraft has "fantastic maintainers" who continually scour the planes for cracks and other problems, Kinzinger said.

"There was always a little, kind of a power struggle between pilots and maintainers, just basically on who owns the aircraft," he said. "They treated them like their babies."

The age of the KC-135 makes it all the more important to press ahead with replacing it with the KC-46A, he said.

"It's not going to be an overnight process," Kinzinger said. "We're talking a couple of decades, and we don't want to get to the point where the KC-135s hit the physical ends of their lives and we don't have a replacement."

The KC-46 is expected to be declared fully operational by September 2018, and plans call for the Air Force to purchase 179 of the new planes by 2027. Right now, the Air Force has 396 KC-135s and 59 KC-10s.

Until the replacement tankers arrive, the Air Force has to live with the risk that there will come a point when KC-135s can no longer fly, said Gregory Cook, a spokesman for that Airlift/Tanker Association.

"If something catastrophic happens and grounds the fleet, we're in trouble because the KC-10 fleet is the only other tanker option we have," Cook said in a Nov. 17 interview.

Stretched thin

The tanker fleet is already so stretched that the Air Force may have problems producing enough tankers for an unexpected scenario, such as operations in Libya in 2011, Cook said. On any given day, the Air Force has tankers set aside for nuclear-capable bombers. Meanwhile, tankers are supporting ongoing operations against the Islamic State group and elsewhere. Tankers are also refueling mobility aircraft and fighters as they cross oceans.

Other tankers are in depot, he said. The older the tankers get, the longer it takes the planes to get through depot.

"When they go through for heavy maintenance, they almost have to rebuild the tanker," Cook said in a Nov. 17 interview. "They have to take it apart. If they find stuff, they have to remanufacture parts that are no longer being produced. They almost have to remanufacture the airplane many times when it goes through a major overhaul."

For its age, the KC-10 holds up remarkably well, said Master Sgt. Eric Austin, lead production superintendent for the 605th Aircraft Maintenance Squadron at Joint Base McGuire-Dix-Lakehurst.

That doesn't mean that KC-10 maintainers are sitting idle on the flightline, he said.

"As for the ops tempo with the KC-10, it's in high demand, as we say, so we meet a lot of mission requirements," Austin said.

Because the KC-10 carries a lot of fuel, the plane's fuel system requires a good deal of maintenance, he said.

"Fuel leaks on tanker aircraft aren't that uncommon, and that's something that we have to deal with on a daily basis," Austin said. "To be expected when you're carrying upwards of 300,000 pounds of fuel on the aircraft."

Still, the KC-10s are in such high demand that it can be challenging to make sure they get all the maintenance they need, he said. That's why maintainers do as much preventive maintenance as possible.

"We don't just fly them until they break," Austin said. "We recognize when discrepancies are piling up and park it and fix it."

Tankers are not the Air Force's "show pony," but it is vital for people to understand that tankers link the continental U.S. and the rest of the world, said Col. John Price, commander of the 305th Air Mobility Wing at Joint Base McGuire-Dix-Lakehurst.

"Sometimes, that KC-10 brings the open hand, as we did in Nepal," following the April earthquake, Price said. "It's the helping hand that is helping folks that couldn't help themselves. We respond to the other side of the world in a way that no other nation in the world can do. That's just straight up awesome. Tankers need to be part of that 'well done.'

"In the same way, the KC-10 is hauling a B-2 across the Atlantic to put a nice piece of warm iron on somebody's front doorstep. We'll talk about the B-2 — or maybe we won't — but we don't talk about the tanker. Yet the B-2 is not going to get from Whiteman Air Force Base [in Missouri] to the other side of the globe without a long string of tankers."