The Lockheed/Boeing/General Dynamics YF-22 is an American single-seat, twin-engine fighter aircraft technology demonstrator designed for the United States Air Force (USAF). The design was a finalist in the USAF's Advanced Tactical Fighter competition, and two prototypes were built for the demonstration/validation phase of the competition. The YF-22 won the contest against the Northrop YF-23, and entered production as the Lockheed Martin F-22 Raptor. The YF-22 has a similar aerodynamic layout and configuration as the F-22, but with differences in the position and design of the cockpit, tail fins and wings, and in internal structural layout. In the 1980s, the USAF began looking for a replacement for its fighter aircraft, especially to counter the advanced Su-27 and MiG-29. A number of companies, divided into two teams, submitted their proposals. Northrop and McDonnell Douglas submitted the YF-23. Lockheed, Boeing and General Dynamics proposed and built the YF-22, which, although marginally slower and having a larger radar cross-section, was more agile than the YF-23. Primarily, for this reason, it was picked by the Air Force as the winner of the ATF in April 1991. Following the selection, the first YF-22 was retired to a museum, while the second prototype continued flying until an accident relegated it to the role of an antenna test vehicle. Design and development In 1981, the U.S. Air Force developed a requirement for an Advanced Tactical Fighter (ATF) as a new air superiority fighter to replace the F-15 Eagle and F-16 Fighting Falcon. This was made more crucial by the emerging worldwide threats, including development and proliferation of Soviet MiG-29 and Su-27 "Flanker"-class fighter aircraft. It would take advantage of the new technologies in fighter design on the horizon including composite materials, lightweight alloys, advanced flight-control systems, more powerful propulsion systems and stealth technology. In September 1985, the Air Force sent out technical request for proposals (RFP) to a number of aircraft manufacturing teams. The seven bids were submitted in July 1986, and two companies, Lockheed and Northrop, were selected on 31 October 1986. The two teams, Lockheed/Boeing/General Dynamics and Northrop/McDonnell Douglas, undertook a 50-month demonstration phase, culminating in the flight test of the two teams' prototypes, the YF-22 and the YF-23. The YF-22 was designed to meet USAF requirements for survivability, supercruise, stealth, and ease of maintenance. Because Lockheed's submission was selected as one of the winners, the company, through its Skunk Works division, assumed leadership of the