in March 1972. Though the Boeing Model 908-909 was initially most favored, it was quite similar in technology and appearance to the cheaper General Dynamics Model 401-16B. Since one of the goals of the program was to validate emerging technologies, Secretary of the Air Force Robert Seamans chose to select the General Dynamics and Northrop entries. The first YF-16 had its official maiden flight on 2 February 1974. The second YF-16 prototype first flew on 9 May 1974. This was followed by the first flights of the Northrop’s YF-17 prototypes, which were achieved on 9 June and 21 August 1974, respectively. The fly-off commenced in 1974 as both prototypes were delivered. The YF-16s would complete 330 sorties during the flyoff, accumulating a total of 417 flight hours; the YF-17s would accomplish 268 sorties. Air Combat Fighter competition Three factors would converge to turn the LWF into a serious acquisition program. First, four North Atlantic Treaty Organization (NATO) members – Belgium, Denmark, the Netherlands, and Norway – were looking to replace their F-104G fighter-bomber variants of the Lockheed F-104 Starfighter interceptor; furthermore, they were seeking an aircraft that their own aerospace industries could manufacture under license, as they had the F-104G. In early 1974, they reached an agreement with the U.S. that if the USAF placed orders for the aircraft winning the LWF flyoff, they would consider ordering it as well. Secondly, while the USAF was not particularly interested in a complementary air superiority fighter competing with F-X, it did need to begin replacing its F-4 and Republic F-105 Thunderchief fighter-bombers. In April 1974, U.S. Secretary of Defense James R. Schlesinger announced that the LWF program would be redirected to a multirole fighter design in the new Air Combat Fighter (ACF) competition. ACF would not be a pure fighter, but more of a fighter-bomber, which essentially ended opposition from the F-X group. Finally, the U.S. Congress was seeking to achieve greater commonality in fighter procurements by the Air Force and Navy. In August 1974, Congress redirected funds for the Navy’s VFAX program to a new Navy Air Combat Fighter (NACF) program that would essentially be a navalized variant of ACF. These requirements meshed relatively well, but the timing of the procurement was driven by the timeframe needs of the four allies, who had formed a "Multinational Fighter Program Group" (MFPG) and were pressing for a U.S. decision by December 1974. The