Test of Gremlin drones a near success, but C-130 couldn't retrieve them By (0) A test of the X61-A Gremlin unmanned aerial vehicle ended without the retrieval of the vehicles by a cargo plane, DARPA said on Thursday. Photo courtesy of DARPA Dec. 11 (UPI) -- X-61A unmanned aerial vehicles flew successfully in a test but could not be retrieved by a cargo plane, the Defense Advanced Research Projects Agency said. It was the third test of the vehicles, nicknamed Gremlins Air Vehicles. Three were launched at an undisclosed location in tests beginning in late October, DARPA said in a statement on Thursday.