design in the 25,000 lb (11,300 kg) class which would out-perform the MiG-21 by 25%. Boyd used his E-M theory to argue that the F-X design was far too heavy, and this led to new requirements for a smaller F-X in the 40,000-pound (18,100 kg) class. However, the appearance of the Mach-3-capable MiG-25 in July 1967 led to serious concerns within the Defense Department that the Soviets had developed a super fighter capable of outrunning anything the US fielded, while its huge wing would make it highly maneuverable. In response, the ADF effort was essentially ignored in favour of an all-out effort to develop a superior F-X, which would emerge as the F-15 Eagle. Boyd was unimpressed with the resulting weight growth in the F-15, and the shelving of the ADF. In the late 1960s he gathered a group of like-minded innovators that became known as the "Lightweight Fighter Mafia". In 1969, this "Fighter Mafia" was able to secure funds for a "Study to Validate the Integration of Advanced Energy-Maneuverability Theory with Trade-Off Analysis". General Dynamics received $49,000 and Northrop $100,000 study contracts to design concepts that embodied Boyd's E-M theory – a small, low-drag, low-weight, pure fighter with no bomb racks; their work would lead to the YF-16 and YF-17, respectively. Although the Air Force’s F-X proponents remained hostile to the concept because they perceived it as a threat to the F-15 program, the ADP concept (revamped and renamed as the "F-XX") gained civilian political support under the reform-minded Deputy Secretary of Defense David Packard, who favored the idea of competitive prototyping. As a result, in May 1971 the Air Force Prototype Study Group was established, with Boyd a key member. Two of its six proposals would be funded, one being the Lightweight Fighter (LWF). The Request for Proposals (RFP) was issued 6 January 1972, and called for a 20,000 lb (9,100 kg) class fighter with a good turn rate, acceleration and range, and optimized for combat at speeds of Mach 0.6–1.6 and altitudes of 30,000–40,000 ft (9,150–12,200 m). This was the region in which the USAF expected most future air combat to occur, based on studies of the Vietnam, Six-Day, and Indo-Pakistani wars. The anticipated average flyaway cost of a production version was $3 million. Five manufacturers – Boeing, General Dynamics, Lockheed, Northrop, and Vought – submitted proposals. The Vought V-1100 and the Lockheed CL-1200-2 Lancer were eliminated