Over the last 15 years, the idea of "killer robots" has morphed from science fiction to reality, with unmanned systems now a common feature in post–9/11 conflict zones. Just about everyone fighting the multi-sided war in Iraq and Syria, for instance, has used drones, from the US and Russia to the Syrian government and Hezbollah to the Islamic State.As robots have become more commonplace on the battlefield, fear has grown that they may be on their way to becoming too independent, too intelligent, and too autonomous, able to do more and more on their own without being steered from afar by human control or restriction.This is the topic of a United Nations–led meeting — entitled the "Meeting of Experts on Lethal Autonomous Weapons Systems" — wrapping up Friday in Geneva. The goal for many at this session is to fight a looming future, to ban the technology and ensure that a human stays at the center of the most important decision in war.But that ship may already have sailed — without need of a crew.