Last August, several dozen military drones and tank-like robots took to the skies and roads 40 miles south of Seattle. Their mission: Find terrorists suspected of hiding among several buildings. So many robots were involved in the operation that no human operator could keep a close eye on all of them. So they were given instructions to find--and eliminate--enemy combatants when necessary. The mission was just an exercise, organized by the Defense Advanced Research Projects Agency, a blue-sky research division of the Pentagon; the robots were armed with nothing more lethal than radio transmitters designed to simulate interactions with both friendly and enemy robots.