The Advanced Tactical Fighter (ATF) was a demonstration and validation program undertaken by the United States Air Force to develop a next-generation air superiority fighter to counter emerging worldwide threats, including Soviet Sukhoi Su-27 and Mikoyan MiG-29 fighters under development in the 1980s. Lockheed and Northrop were selected in 1986 to develop the YF-22 and the YF-23 demonstrator aircraft. These aircraft were evaluated in 1991 and the Lockheed YF-22 was selected and later developed into the F-22 Raptor.