<hi style=afpcap>The Air Force has for several decades issued a request for proposals for each major aircraft requirement with the two most favoured designs being funded for a pair of prototypes to compete against one another. The Advanced Tactical Fighter originated in the early '80s for a new aircraft type which would be the air superiority fighter for the next century. In both cases a consortium of leading manufacturers amalgamated to bid for this potentially lucrative project, with Lockheed, Boeing and General Dynamics offering their YF-22A, while Northrop and McDonnell Douglas teamed together with their YF-23A (illustrated). In both cases the two prototypes were powered by different engines enabling the Air Force to select the most suitable aircraft type and the best powerplant at the same time. The YF-23A was not selected as the winning design, with the two prototypes being transfered to NASA at Edwards AFB at the completion of the test phase. </hi>
