From the spears hurled by Romans to the missiles launched by fighter pilots, the weapons humans use to kill each other have always been subject to improvement. Militaries seek to make each one ever-more lethal and, in doing so, better protect the soldier who wields it. But in the next evolution of combat, the U.S. Army is heading down a path that may lead humans off the battlefield entirely.

Over the next few years, the Pentagon is poised to spend almost $1 billion for a range of robots designed to complement combat troops. Beyond scouting and explosives disposal, these new machines will sniff out hazardous chemicals or other agents, perform complex reconnaissance and even carry a soldier's gear.

"Within five years, I have no doubt there will be robots in every Army formation," said Bryan McVeigh, the Army's project manager for force protection. He touted a record 800 robots fielded over the past 18 months. "We're going from talking about robots to actually building and fielding programs," he said. "This is an exciting time to be working on robots with the Army."