More than 40 countries — including the United States, Great Britain, Russia and China — are developing a new generation of robotic weapons that can be programmed to seek out and destroy enemy targets without direct human control. The push for autonomous machines has raised a host of legal and ethical questions and sparked concerns that the Geneva Conventions — international rules of war that date back to the 1860s — may not be adequate to control robotic warfare. Military experts say autonomous weapons could save lives by keeping soldiers out of harm's way and by using pinpoint accuracy to avoid civilian deaths and other collateral damage. But opponents fear the emerging technology might trigger a new arms race and encourage leaders to use force rather than diplomacy. Meanwhile, the U.S. military is developing revolutionary ways to supply and protect soldiers, including Kevlar underwear, invisible camouflage and customizable 3D-printed food.