On 1 December 1977, a strange, faceted aircraft nicknamed the "Hopeless Diamond" lifted off from Groom Lake, Nevada, and vanished from radar before it vanished into the sky. Have Blue, built by Lockheed’s Skunk Works under a DARPA program code-named "Experimental Survivability Testbed," was the first practical combat stealth aircraft. Its origins lay in the work of Soviet physicist Pyotr Ufimtsev, whose 1962 paper on electromagnetic diffraction was translated by the U.S. Air Force and fed into a Lockheed computer program called Echo 1. The Skunk Works team, led by Ben Rich and employing mathematician Bill Schroeder, used Ufimtsev’s equations to design a shape of flat, tilted panels that deflected radar waves away from the receiver. The two Have Blue demonstrators were built with $10 million of Lockheed’s own money and $20 million from classified Air Force funds. Test pilots Bill Park and Ken Dyson flew them against air-defense radars; only the T-38 chase plane ever appeared on the screens. The first Have Blue crashed on 4 May 1978; the second was lost on 11 July 1979. But their eighteen-month test series proved that an aircraft could be all but invisible—and that proof led directly to the F-117 Nighthawk, the B-2 Spirit, and the fifth-generation fighters that now rule the skies.