The Pentagon has confirmed a number of “unauthorized” drone flights last year in restricted airspace over a Virginia base that houses the nation’s most advanced fighter jets. The Wall Street

U.S. officials don’t know who is behind the drones that have flown unhindered over sensitive national-security sites—or how to stop them.

The military and the Pentagon’s UFO investigating arm have tried to determine the source of the drones that flew over Langley Air Force Base.