The Lockheed F-117 Nighthawk is an officially retired American single-seat, subsonic, twin-engined stealth attack aircraft developed by Lockheed's secretive Skunk Works division and operated by the United States Air Force (USAF). It was the first operational aircraft to be designed with stealth technology.

Work on what would become the F-117 commenced in the 1970s as a means of countering increasingly sophisticated Soviet surface-to-air missiles (SAMs). During 1976, the Defense Advanced Research Projects Agency (DARPA) issued Lockheed a contract to produce the Have Blue technology demonstrator, the test data from which validated the concept. On 1 November 1978, Lockheed decided to proceed with the F-117 development program. Five prototypes were produced; the first of which performed its maiden flight in 1981 at Groom Lake, Nevada. The first production F-117 was delivered in 1982, and its initial operating capability was achieved in October 1983. All aircraft were initially based at Tonopah Test Range Airport, Nevada.

The aircraft's faceted shape (made from two-dimensional flat surfaces) heavily contributes to its relatively low radar cross-section of about 0.001 m² (0.0108 sq ft). To minimize its infrared signature, it has a non-circular tail pipe that mixes hot exhaust with cool ambient air and lacks afterburners; it is also restricted to subsonic speeds, as breaking the sound barrier would produce an obvious sonic boom that would increase both its acoustic and infrared footprints. While commonly referred to as the "Stealth Fighter", the aircraft was designed and employed as a dedicated attack aircraft, and indeed its performance in air combat maneuvering was less than that of most contemporary fighters. The F-117 is equipped with integrated sophisticated digital navigation and attack systems, targeting being achieved via a thermal imaging infrared system and a laser rangefinder/laser designator. It is aerodynamically unstable in all three aircraft principal axes, thus requiring constant flight corrections via a fly-by-wire flight system to maintain controlled flight.

Even in the years following its entry to service, the F-117 was a black project, its existence being denied by USAF officials. On 10 November 1988, the F-117 was publicly acknowledged for the first time. Its first combat mission was flown during the United States invasion of Panama in 1989. The last one of 59 production F-117s was delivered on 3 July 1990. The F-117 was widely publicized for its role in the Gulf War of 1991, having flown around 1,300 sorties and scored direct hits on what the US military described as 1,600 high-value targets in Iraq. F-117s also participated in the conflict in Yugoslavia, during which one was shot down by a SAM in 1999. It was also active during Operation Enduring Freedom in 2001 and Operation Iraqi Freedom in 2003. The USAF retired the F-117 in 2008, primarily due to the fielding of the F-22 Raptor. Despite the type's official retirement, a portion of the F-117 fleet has been kept in airworthy condition, and some have been observed flying since being retired from combat. It has been flown by the USAF for research and development, testing, and training purposes.

In 1936, Robert Watson Watt, the British radar pioneer, noted that measures to reduce an object's radar cross-section (RCS) could be used to evade radar detection. In 1962, Pyotr Ufimtsev, a Soviet mathematician, published a seminal paper titled "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 the radar return from an object is related to its edge configuration, not its size. Ufimtsev was extending theoretical work published by German physicist Arnold Sommerfeld. Ufimtsev demonstrated that he could calculate the RCS across a wing's surface and along its edge. The obvious and logical conclusion was that even a large aircraft could reduce its radar signature by exploiting this principle. However, the resulting design would make the aircraft aerodynamically unstable, and the state of computer technology in the early 1960s could not provide the kinds of flight computers that would later allow aircraft such as the F-117 and B-2 Spirit to stay airborne. By the 1970s, when Lockheed analyst Denys Overholser found Ufimtsev's paper, computers and software had advanced significantly, and the stage was set for the development of a stealth airplane.

The F-117 was conceived after the Vietnam War, where increasingly sophisticated Soviet SAMs had downed heavy bombers. The heavy losses inflicted by Soviet-made SAMs upon the Israeli Air Force in the 1973 Yom Kippur War also contributed to a 1974 Defense Science Board assessment that in case of a conflict in Central Europe, air defenses would likely prevent NATO air strikes on targets in Eastern Europe.

It was a black project, remaining an ultrasecret program for much of its life. The project began in 1975 with a model called the "Hopeless Diamond" (a wordplay on the Hope Diamond because of its appearance). The following year, the Defense Advanced Research Projects Agency (DARPA) issued Lockheed Skunk Works a contract to build and test two Stealth Strike Fighters, under the code name "Have Blue". These subscale aircraft incorporated jet engines of the Northrop T-38A, fly-by-wire systems of the F-16, landing gear of the A-10, and environmental systems of the C-130. By bringing together existing technology and components, Lockheed built two demonstrators under budget, at $35 million for both aircraft, and in record time. Undersecretary of Defense for Research and Engineering William J. Perry was instrumental in shepherding the project.

The maiden flight of the demonstrators occurred on 1 December 1977. Although both aircraft crashed during the demonstration program, test data gathered proved positive. The success of Have Blue led the government to increase funding for stealth technology. Much of that increase was allocated towards the production of an operational stealth aircraft, the Lockheed F-117, under the program code name Senior Trend.