This week, "Salty Dog 502"—one of the Navy's two X-47B carrier-based unmanned aircraft— did something no other drone has ever done: it lined itself up behind a human-flown tanker plane and pulled up for a fill-up. While the technology used for the refueling had been previously tested and demonstrated on a manned Lear jet acting as an "unmanned aircraft surrogate testbed," this was the first time that a drone had completely autonomously flown in behind a tanker plane and completed an actual refueling.



In-flight refueling extends the range of military aircraft, allowing them to stay in the air longer while on patrol and fly extended long-range missions. The refueling plane used in the test, a modified Boeing 707, belonged to Omega Air Refueling, a DOD contractor that provides refueling to Navy and Marine Corps planes and the air forces of other countries. The test was important because of the roles envisioned for carrier-launched drones in the future: combat air patrol around carrier groups, persistent surveillance, and long-range attack missions.

The X-47B flies autonomously, guided by commands from a desktop application rather than by a pilot with remote controls. It was the first unmanned aircraft to ever perform a carrier landing with a tailhook capture (though other drones have been flown from ships, they have either been unmanned helicopters or were small drones captured by hook or net). And while drones have conducted in-flight refueling tests before—DARPA and NASA performed a test using two Northrop Global Hawks—those unmanned aircraft have been piloted by humans remotely.

With that first test completed, both X-47Bs are headed to retirement. Because of the differences in size and performance between the X-47B and the as-yet-to-be-finalized Unmanned Carrier Launched Surveillance and Strike (UCLASS) combat drone, the Navy has decided to stick with surrogate aircraft for further tests of systems that might be adapted for UCLASS. So the only future flying that Salty Dog 501 and Salty Dog 502 will be doing will be aided by cables in a museum display. While the drones have dodged retirement in the past—they were nearly mothballed in 2013—it's unlikely that they will be called back into service.

They will be fairly pricey museum pieces: the X-47B program was awarded to Northrop Grumman in 2007, under a $635.8 million contract that would eventually grow to $813 million by 2012. The refueling test flights were part of a $63 million "post-demonstration" development contract.