American air dominance has long rested on staying technologically ahead of the enemy. With high-speed stealth design, advanced avionics, and integrated computing, the fifth-generation F-35 Lightning II is built to keep that edge for the United States and its allies. The problem—aside from a spate of cost overruns, malfunctions, and delays—is that other countries are no longer far behind. The Chinese J-31 Gyrfalcon 1 resembles the F-35 not just in looks, but also in speed and strike capabilities. The Russian T-50 PAK FA is a fifth-generation fighter jet whose capabilities parallel those of the U.S. F-22. As more countries reach the technology frontier, the advantage gained by any one of them diminishes. And so military planners are looking for another edge: unmanned craft. That means the F-35 could earn a different distinction: As the U.S. Secretary of the Navy Ray Mabus said in April, it "should be, and almost certainly will be, the last manned strike fighter aircraft the Department of the Navy will ever buy or fly."