The first YF-23, with Pratt & Whitney engines, supercruised at Mach 1.43 on Sep. 18, 1990, while the second, with General Electric engines, reached Mach 1.6 on Nov. 29, 1990. By comparison, the YF-22 achieved Mach 1.58 in supercruise. During the late 1970s, a new generation of Soviet fighters and Surface-to-Air Missiles (SAMs) prompted the U.S. Air Force (USAF) to find a replacement for the F-15 Eagle air superiority fighter.For this reason in 1986, the USAF awarded demonstration contracts to two competing industry teams, the Lockheed-Boeing-General Dynamics (whose proposal was the YF-22A) and the Northrop-McDonnell Douglas (whose proposal was the YF-23A), which would have competed one versus the other in the Advanced Tactical Fighter (ATF) program.The Northrop YF-23A was designed to meet USAF needs for survivability, ease of maintenance and supercruise. To satisfy the latter requirement two different engines (the Pratt & Whitney YF119-PW-100L and the General Electric YF120) were competing one versus the other too. Called Augmented Turbofans, these new engines would have allowed both the YF-22 and the YF-23 to fly supersonic without using the afterburner, resulting in fuel savings and increased combat radius and effectiveness.