Lockheed F-117A Stealth Fighter DEVELOPMENT HISTORY
Another development since World War II is that radar has created an open battle field for aircraft. Any attack in enemy territory involved the risk of being detected early - in fact, in the late 60s, the risk was a certainty, without an extensive array of radar jamming equipment, radar warning devices and chaff-bombs. Often, these were carried by other aircraft, with strike aircraft headed for the primary target, and the majority of the aircraft in a mission acting as defense-suppression aircraft.
Jamming techniques struggled, and often failed, to keep up with new radar technology. Radar absorbent materials (RAM) were being developed, but did not in themselves provide the necessary reduction in radar cross-section (RCS) to be of real benefit. Some engineers envisaged a more comprehensive solution. In 1975, the US Air Force held a Radar Camouflage Symposium, the proceedings of which have not yet been declassified. The same year, Engineers at Lockheed's 'Skunk Works' designed an aircraft with hardly any curved surfaces at all. The simple concept was that a sharp edge reflects much less radiation than a rounded surface. The trick was in predicting every possible path of reflected radiation from its source to the aircraft to its final direction, and this was only possible with the new computer technology becoming available in the late 70s.
After some tests on the basic shape, Lockheed obtained funding from the Defense Advanced Research Project Agency (DARPA) for two sub-scale flying prototypes of a stealth attack aircraft. Code named, Have Blue, the project went ahead, after control was transferred for security reasons from the civilian DARPA to the USAF. Little was heard publicly of stealth until the mid 80s.
The first Have Blue prototype flew in early 1978, testing flying characteristics. The second was given the complete stealth treatment, with RAMs and tightly-fitted panels, for tests against captured Soviet radar-guided missiles and other threats. The first prototype was lost in a crash due to a high vertical speed on final approach, but the second went on to prove the capability of a nearly radar invisible design, before itself crashing.
The full-scale development program was code-named Senior Trend, and a full-size F-117A was flown on June 18th 1982. The aircraft is not known to have an official name, but is variously known as Stealth Fighter, Nighthawk, and Black Jet. The Groom Lake development testing team named it the Scorpion. "
From the manual