The codename of the US stealth aircraft demonstrator program was Have Blue. Developed by Lockheed’s Skunk Works for the US government, it tested whether an aircraft could be designed with an exceptionally small radar cross-section.
The project grew out of the Experimental Survivable Testbed, or XST, competition in the 1970s. Lockheed’s winning design used sharply faceted surfaces to scatter radar energy away from the transmitter. Engineers drew on the mathematical work of Soviet physicist Pyotr Ufimtsev, whose research helped make radar-reflection calculations practical with emerging computer tools.
Two flyable Have Blue demonstrators were built. The first flew at Groom Lake, Nevada, on 1 December 1977. Both aircraft were eventually lost to accidents, but the tests successfully demonstrated the concept and its flight-control challenges. The faceted aircraft acquired the nickname “Hopeless Diamond.”
Have Blue was not the operational stealth fighter itself. Its success led to Senior Trend, the development program that produced the Lockheed F-117 Nighthawk. Tacit Blue was a separate Northrop stealth demonstrator, while F-22 is an operational fighter rather than a demonstrator codename.