In 1968, the United States started a new aircraft project following the development of the high-performance interceptor Mig-25 by the Soviet Union. The requirements of the F-X project were 40,000 lb. MTOW, a maximum speed of 2.5 Mach, and a high thrust-to-weight ratio. In 1969, McDonnell-Douglas's F-15 was selected, leading the way to the birth of the fighter that would replace the F-4 Phantom II. It carried a powerful radar (APG-63) and plenty of missiles (4 AIM-7 and 4 AIM-9) to deal with the Mig-25. As the F-X project continued, the challenges of equipping the Air Force with such a capable and expensive aircraft began to arise. The team that led the debate was nicknamed the "Fighter Mafia" at the time. The core staff of this team was Colonel John Boyd, Colonel Everest Riccioni, Analyst Pierre Spray, and Engineer Harry Hillaker. The Fighter Mafia believed that the ideal fighter should be light and highly maneuverable. Thus, it could easily change its speed, altitude, and direction. Also, it would be difficult to detect the light and, therefore, the small plane. It would also be cheap to manufacture and operate. Later, Boyd and his team received funding from Northrop and General Dynamics to develop these concepts. The Air Force did not support these efforts, as it would undermine the F-15 (Project F-X). Finally, they realized that the budget would not be enough to get enough F-15s and then the Fighter Mafia's ideas started to be valued. The Advanced Day Fighter concept emerged and was named the F-XX project. With the support of the Department of Defense, the Air Force Prototype Study Group was established in May 1971. Two of the six candidates were selected, and the Lightweight Fighter (LWF) project was initiated. The request for proposal was published on June 6, 1972. In light of the lessons learned from the Vietnam War, the Six-day War, and the Indo-Pakistan conflicts, the USAF requested a fast and high maneuverable aircraft that weighs 20 tons and is optimized for combat at Mach 0.6 - 1.6 at an altitude of 30,000 - 40,000 feet. In May 1972, the proposals of General Dynamics and Northrop were selected, and the YF-16 and YF-17 prototypes were manufactured. The prototypes made their maiden flights on February 2, 1974, and June 9, 1974, respectively. That same year, NATO members Belgium, Denmark, the Netherlands, and Norway wanted to replace their F-104Gs. The winner of the LWF project would also have the opportunity to be sold to these countries when the U.S. Air Force's desire to replace its F-4 and F-105 aircraft, combined with these countries' need for a new fighter-bomber, the LWF project turned into the Air Combat Fighter (ACF). The YF-16 aircraft had also evolved into a multi-role fighter from a day fighter, and the number of its underwing pylons was increased from two to three. The radar requirements were also changed, and the Westinghouse APG-66 multi-mode mission radar was selected. 

On June 13, 1975, the U.S. Air Force announced that it had chosen the YF-16. In this choice, the P&W F100 turbofan engines used in the F-15 aircraft played a significant role as much as the YF-16's superior acceleration, climbing, and maneuverability to the YF-17. This selection also reduced engine unit costs and operating costs.