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English: The air superiority fighter development was one of the U.S. Air Force highest priority objectives of the late 1960s, to combat the Migs, and their successors, in the mid-1970s and beyond. USAF started the engine development program for such a fighter in cooperation with the U.S. Navy, and by the mid-1969 they have had three aircraft manufacturers working on the fighter itself. The aircraft companies were under contract to design the best possible single-seat, twin-engine fighter for air-to-air combat, type classified as F-15. While the F-15 designs were not complete, the USAF had a good idea of their general characteristics. With the takeoff weight or the F-15 in the 40,000-pound class, the thrust-to-weight ratio was to be very good. This high thrust-to-weight ratio, in combination with a much lower wing loading than the USAF have had in recent fighters, was to provide acceleration and maneuverability better than anything flying, or that foreseeable on either side of the Iron Curtain. This performance assured the close-in maneuvering ability necessary for winning air battles and maintaining air superiority.