Last August, U.S. Navy operators on the ground lost all contact with a Fire Scout helicopter flying over Maryland. They had programmed the unmanned aerial vehicle to return to its launch point if ground communications failed, but instead the machine took off on a north-by-northwest route toward the nation’s capital. Over the next 30 minutes, military officials alerted the Federal Aviation Administration and North American Aerospace Defense Command and readied F-16 fighters to intercept the pilotless craft. Finally, with the Fire Scout just miles shy of the White House, the Navy regained control and commanded it to come home. “Renegade Unmanned Drone Wandered Skies Near Nation’s Capital,” warned one news headline in the following days. “UAV Resists Its Human Oppressors, Joyrides over Washington, D.C.,” declared another.

The Fire Scout was unarmed, and in any case hardly a machine with the degree of intelligence or autonomy necessary to wise up and rise up, as science fiction tells us the robots inevitably will do. But the world’s biggest military is rapidly remaking itself into a fighting force consisting largely of machines, and it is working hard to make those machines much smarter and much more independent. In March, noting that “unprecedented, perhaps unimagined, degrees of autonomy can be introduced into current and future military systems,” Ashton Carter, the U.S. undersecretary of defense for Acquisition, Technology and Logistics, called for the formation of a task force on autonomy to ensure that the service branches take “maximum practical advantage of advances in this area.”

In Iraq and Afghanistan, U.S. troops have been joined on the ground and in the air by some 20,000 robots and remotely operated vehicles. The CIA regularly slips drones into Pakistan to blast suspected Al Qaeda operatives and other targets. Congress has called for at least a third of all military ground vehicles to be unmanned by 2015, and the Air Force is alr...