Flying an F-16 fighter jet on a long reconnaissance mission is about as efficient as driving a Formula One racecar to the grocery store. Its swept wings have great maneuverability at high speeds, but to stay aloft for hours at a time, you’d be better off with a slower, straight-wing craft such as the U.S. Air Force’s unmanned reconnaissance vehicle Global Hawk. But what if you need to monitor vast tracts of land and respond at a moment’s notice to enemy activity?