For years the United States has enjoyed almost exclusive use of armed drones, using them to strike enemies remotely and with impunity.
But with adversaries — including ISIS — catching up on the technology, the Pentagon is now playing defense, trying to come up with ways to knock the pilotless aircraft out of the sky.
Much of the U.S. military's research into fighting drones is secret. But contracting and budget documents show that officials are exploring a range of approaches, from the tried and true — machine guns — to cutting-edge technology that includes electronic jamming and laser cannons.
Maryland, with its complex of military...