First flying in 1972, the McDonnell Douglas F-15 Eagle has transitioned from a true air superiority fighter into an all-weather strike aircraft. Thus far, the aircraft has compiled one of the most enviable records of a post-Vietnam fighter, logging more than 100 victories and no losses in air-to-air combat. The bulk of the fighter aircraft operated by the USAF in Vietnam had been conceived during the Cold War as interceptors against nuclear-armed Soviet bombers. This strategy involved high-altitude, high-speed, air-to-air missile armament, and a long range. Utilizing these aircraft in Vietnam, with visual engagement rules, pointed to the shortcomings of the planning. Though both the F-105 and F-4 were deployed to Vietnam, neither were truly optimized for the role that they were forced into. Further shortcomings of the then-current fighter strategy was revealed in July 1967 when the Soviet's unveiled the MiG-25 Foxbat. The Foxbat was a twin tail, twin engine fighter aircraft capable of Mach 2.8. The US Air Force responded with renewed interest in what was then known as the F-X program. This program had begun as an effort to develop a multirole aircraft with variable geometry wings. After briefly considering a lightweight, single engine fighter, a concept discarded in light of the shortcomings of the F-104, Project Definition Phase (PDP) contracts were issued to Fairchild-Republic, McDonnell Douglas, and North American Rockwell on December 30, 1968. After considering the proposals advanced by all three firms, a design and development contract was issued to McDonnell Douglas for the aircraft that would be designated F-15.