The F-117 was born after combat experience in the Vietnam War when increasingly sophisticated Soviet surface-to-air missiles (SAMs) downed heavy bomber flights.
In 1964, Pyotr Ya. Ufimtsev, a Soviet/Russian mathematician, published a seminal paper, “Method of Edge Waves in the Physical Theory of Diffraction”, in the Journal of the Moscow Institute for Radio Engineering, in which he showed that the strength of a radar return is related to the edge configuration of an object, not its size. Ufimtsev was extending theoretical work published by the German physicist Arnold Sommerfeld. Ufimtsev demonstrated that he could calculate the radar cross-section across a wing’s surface and along its edge. The obvious conclusion was that even a large airplane could be made stealthy by exploiting this principle. However, the airplane’s design would make it aerodynamically unstable, and the state of computer technology in the early 1960s could not provide the kinds of flight computers which allow aircraft such as the F-117, and B-2 Spirit to stay airborne. However, by the 1970s, when a Lockheed analyst reviewing foreign literature found Ufimtsev’s paper, computers and software had advanced significantly, and the stage was set for the development of a stealthy airplane.