“In the 1970s, a key piece of the stealth formula emerged when the Americans discovered an obscure 20-year-old scientific paper by Pyotr Ufimtsev, a Russian scientist who had proposed reducing RCS by building an aircraft with flat surfaces and irregular angles, rather than the usual aerodynamically streamlined profile. Bill Schroeder, a mathematician for aircraft maker Lockheed (now Lockheed Martin), developed a computer program that made it possible to predict precisely the RCS of such an aircraft exterior.”
http://dsc.discovery.com/convergence/stealth/article/article.html