Since the incorporation of the airplane into military service, air superiority has been a key ingredient to success on the modern battlefield. Global Engagement: A Vision For the 21st Century Air Force, the USAF's latest vision statement, lists air and space superiority as the first of six Air Force core competencies. The F-15 Eagle is currently the USAF's primary air superiority fighter. Designed in the 1960s and introduced into service in the mid-1970s, the F-15's status as the world's premiere air superiority fighter is being challenged by new fighter designs from numerous countries, as well as the proliferation of advanced surface-to-air missile systems. The F-22 is the USAF's follow-on air superiority fighter to the F-15. The design features of stealth, supersonic cruise, integrated avionics, and sustained maneuverability will provide the F-22 with a first shot/first kill capability in all environments, against all current and planned future threats. However, at $102 million a copy, the F-22 is by far the most expensive fighter the USAF has ever persued. Along with the collapse of the Soviet Union, today's environment of shrinking defense budgets has called into question the necessity of buying the F-22 at all. Although there are a number of less expensive alternatives, none of them approach the combat capability of the F-22. The USAF is scheduled to buy 339 F-22s which will reach operational capability in late 2004. This schedule must be maintained in order to ensure the USAF can provide air superiority for U.S. forces in the future.