In the summer of 1975, the Defense Advanced Research Projects Agency (DARPA) launched a competition that would change the nature of aerial warfare. The challenge was not speed, nor altitude, nor maneuverability. It was invisibility — or as close to it as physics would allow. Lockheed, though not initially invited to participate, lobbied aggressively and was admitted under a symbolic $1 contract. Inside the Skunk Works, engineer Denys Overholser had made a critical discovery: a 1966 Soviet paper by Pyotr Ufimtsev, "Method of Edge Waves in the Physical Theory of Diffraction," translated by the Air Force Foreign Technology Division. Ufimtsev's mathematics showed how to calculate radar cross-sections for geometric shapes. Overholser realized that if an aircraft were composed entirely of flat, angled surfaces — facets — the radar energy could be reflected away from the receiver rather than back toward it.