In what the Navy said was a major breakthrough, an unmanned X-47B aircraft became the first drone to be refueled in mid-air. Flying over the Chesapeake Bay on Wednesday, the aircraft, built by Northrop Grumman, remained steady behind Omega K-707 tanker and received 4,000 pounds of fuel through a long hose, known as a drogue.

The achievement comes at a critical time for unmanned flight. In a speech last week, Navy Secretary Ray Maybus said that pilotless planes “have to be the new normal” in the future. He added that the F-35 Joint Strike Fighter, still in development, “should be, and almost certainly will be, the last manned strike fighter aircraft the Department of the Navy will ever buy or fly.”

And it comes as some members of Congress are pushing the Pentagon to develop autonomous aerial vehicles that could take off and land from aircraft carriers, fly for days at a time (while being refueled), while hauling an arsenal of weapons deep into enemy territory.

Northrop’s X-47B has already flown from carriers—even in concert with piloted F/A 18 Hornet fighter jets. The refueling, officials said, was a significant step toward developing a fleet of drones that will be able to stay aloft for long periods of time.

“What we accomplished today demonstrates a significant, groundbreaking step forward for the Navy,” said Capt. Beau Duarte, the Navy’s Unmanned Carrier Aviation program manager. “The ability to autonomously transfer and receive fuel in flight will increase the range and flexibility of future unmanned aircraft platforms, ultimately extending carrier power projections.”