The YF-23A competed in the late 1980s/early 1990s against the YF-22A in the Advanced Tactical Fighter (ATF) program.During the late 1970s, a new generation of Soviet fighters and Surface-to-Air Missiles (SAMs) prompted the US Air Force to find a replacement for the F-15 Eagle air superiority fighter. In 1986, the USAF awarded demonstration contracts to two competing industry teams—Lockheed-Boeing-General Dynamics (YF-22A) versus Northrop-McDonnell Douglas (YF-23A).The Northrop YF-23A, unofficially named the Black Widow II, emphasized stealth characteristics. To lessen weight and increase stealth, Northrop decided against using thrust vectoring for aerodynamic control as was used on the Lockheed YF-22A. Northrop built two YF-23A prototypes.