(US Air Force photo by Master Sgt Michael Jackson)

On Jan. 25, 2019, officials from Boeing and the Air Force gathered at Everett Field in Washington state to see off the first two KC-46 Pegasus tankers, celebrating with specially made cookies and classic rock.

When the tankers landed at McConnell Air Force Base in Kansas for delivery to the Air Force, it was the culmination of two decades of work, coming after two years of delays and more than $3 billion in penalties incurred by Boeing.


It also came more than six months after Congress made an official suggestion about the Air Force's next tanker.

Fire engines from the 22nd Civil Engineer Squadron fire department salute the first KC-46A Pegasus delivered McConnell Air Force Base, Kansas, Jan. 25, 2019.

(U.S. Air Force photo by Airman Michaela Slanchik)

In their markup of the 2019 defense budget in June 2018, members of the Senate Armed Services Committee expressed concern about growing threats to "large high-value aircraft in contested environments."

The Air Force's tankers allow greater operational availability and range for fighters and bombers, but "these assets are manned and increasingly difficult to protect," the committee said.

"Given the increasingly challenging operating environments our potential adversaries are presenting, it is prudent to explore options for optionally unmanned and more survivable tankers that could operate autonomously as part of a large, dispersed logistics fleet that could sustain attrition in conflict," the committee added.

Committee members recommended an extra $10 million in spending on Air Force research, development, testing, and evaluation — bumping the total to $38.4 million.

A KC-46A Pegasus aerial refueling tanker connects with an F-15 Strike Eagle test aircraft, Oct. 29, 2018.

(US Air Force photo by Master Sgt Michael Jackson)

Those lawmakers are not the first to broach the adoption of unmanned tankers.

Boeing is researching automation for its commercial aircraft, though that is partly an effort to address a protracted pilot shortage affecting commercial and military aviation. Russian aircraft maker Ilyushin is working on a similar project, aiming to develop an unmanned transport aircraft for use remote or difficult-to-reach areas.

In 2016, the Air Force's Air Mobility Command chief, who oversees tankers and other transport aircraft, said the service was looking ahead to advanced technology for the KC-Z — a tanker that could enter contested areas and refuel advanced aircraft.

But Air Force Chief of Staff Gen. David Goldfein said this weekend that the service is no longer looking for at single platforms to address major challenges.

A KC-46A crew member starts to unload cargo at Minot Air Force Base, North Dakota, Sept. 17, 2018.

(U.S. Air Force photo by Staff Sgt Steven M. Adkins)

"The days of buying individual platforms that we then described as game changers — those days are behind us," Goldfein said when asked about potentially buying a stealth tanker to support fifth-generation fighters like the F-35, according to Aviation Week.

"There actually are no silver bullets on the horizon," he added.

The Air Force chief has said the service should look to prepare for a networked battlefield, fielding assets that can connect and share with each other. He returned that theme this weekend, while flying to Andrews Air Force Base.

A KC-46A crew member inspects the refueling boom at Minot Air Force Base, North Dakota, Sept. 17, 2018.

(U.S. Air Force photo by Staff Sgt Steven M. Adkins)

"I actually don't know if the next version of tanker operates in the air or operates at low Earth orbit," he said, according to Aviation Week. "I don't know if it's manned or unmanned, and I actually don't care that much as long as it brings the attributes we need to win."

That new approach may see the head of Air Mobility Command working on the next tanker in coordination with the Air Force Space Command, which Goldfein said "makes perfect sense to me."

While the future of the Air Force's tankers remains open-ended, the KC-46 — of which the Air Force expects at least 36 by the end of 2019 — still has definite goals to meet. Air Force Secretary Heather Wilson, the service's top civilian official, confirmed this month that the tanker's wing refueling pods won't be certified by the FAA until 2020.

This article originally appeared on Business Insider. Follow @BusinessInsider on Twitter.