In the summer of 2003, an Air Force pilot named Greg Harbin was doing desk duty at Prince Sultan Air Base in Saudi Arabia. Day in and day out, Harbin sat in front of five computer screens, scanning photographs and video sent by unmanned planes flying 1,200 miles away, over Iraq and Afghanistan. His job was to take that information, along with reports from ground troops, and identify fresh targets -- Taliban fighters or Iraqi insurgents. But one thing puzzled him. When regular units called for an attack by a Predator drone, the request went to Harbin, and then, if...