Nine airframe companies and three engine manufacturers responded to the challenge when ASD reentered the game and issued its request for information for an ATF in 1981. At this early stage in the program, the Air Force had not decided whether the new aircraft would emphasize air-to-air or air-to-ground missions. The Air Force invited industry to share ideas for a new fighter.
The companies submitted a wide range of configurations in their responses. Lockheed's response favored a derivative of the YF-12A (what most people would recognize as a single-seat SR-71). This aircraft, designed for air-to-ground missions, carried several kinetic-energy penetrator weapons in a central weapon bay. The weapons would be released at supersonic speeds at high altitudes and guided by a laser. The approach, which was worked through spring 1982, built upon technical data gathered from a series of air-to-air missile launches from the YF-12A conducted in the mid- to late-1960s. The YF-12A had fired seven Hughes AIM-47 missiles at altitudes up to 80,000 feet at speeds over Mach 3. The shots, at aerial targets at ranges of over thirty miles, were highly successful. The high-altitude, high-speed approach was also one of Lockheed's candidates for the F-X program, what became the F-15.
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The proposals from most companies for the concept exploration phase showed how they would narrow down their previous approaches for achieving air superiority. This work would lead to the next phase of the program, the demonstration/validation phase, in which they would have to prove their technologies and refine their designs. Lockheed, however, took a radical departure from its high-speed, high-altitude design and started from scratch with an F-117 derivative in its proposal for the concept definition phase.
"Clearly, ATF was going to be superstealth and not a cousin of YF-12 or SR-71," explains Osborne. "I stopped the YF-12 derivative effort, and we started working on an F-117 derivative for ATF." The design submitted in the Lockheed proposal looked like a larger and elongated F-117 with some significant differences. It had a high wing rather than low wing and four tails instead of two. The inlets were placed below and behind the leading edge of the wing. The highly faceted airplane weighed around 80,000 pounds and was far from aerodynamic.
