On August 2, 2010, a U.S. Navy helicopter wandered lazily into the skies of the highly restricted airspace that extends like an invisible dome over the American capital. The event might have merited nothing more than a routine log entry for air-traffic controllers at Ronald Reagan Washington National Airport, except for one disturbing detail. The helicopter had no human pilot. The aircraft had no cutout space for windows, and its cockpit was filled with nothing more than electronic instrumentation. It was a drone.