The Lockheed F-117 Nighthawk was the world's first operational stealth aircraft. Developed in the late 1970s under the code name "Have Blue" at Kelly Johnson's Skunk Works, it used faceted surfaces to deflect radar waves rather than absorb them. The design was so aerodynamically unstable that it required quadruple-redundant fly-by-wire controls. First flight was in 1981; operational status achieved in 1983. The F-117 flew 1,300 combat sorties in the 1991 Gulf War, striking 40% of the strategic targets in Baghdad on the first night. On March 27, 1999, one was shot down over Serbia by a Soviet-era SA-3 missile battery—proving stealth was not invincibility. The F-117 was retired in 2008 as the F-22 Raptor took over its role. The technology pioneered in the F-117 fundamentally changed military aviation design philosophy.