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The Lockheed YF-12 was an American prototype interceptor aircraft evaluated by the United States Air Force. The YF-12 was a twin-seat version of the secret single-seat Lockheed A-12 reconnaissance aircraft, which led to the U.S. Air Force's Lockheed SR-71 Blackbird twin-seat reconnaissance variant. The YF-12 set and held speed and altitude world records of over 2,000 mph and over 80,000 ft (later surpassed by the SR-71), and is the world's largest manned interceptor to date. ==Design and development== In the late 1950s, the United States Air Force (USAF) sought a replacement for its F-106 Delta Dart interceptor. As part of the Long Range Interceptor Experimental (LRI-X) program, the North American XF-108 Rapier, an interceptor with Mach 3 speed, was selected. However, the F-108 program was canceled by the Department of Defense in September 1959.〔Pace 2004, pp. 45–46.〕 During this time, Lockheed's Skunk Works was developing the A-12 reconnaissance aircraft for the Central Intelligence Agency (CIA) under the ''Oxcart'' program. Kelly Johnson, the head of Skunk Works, proposed to build a version of the A-12 named AF-12 by the company; the USAF ordered three AF-12s in mid-1960.〔Pace 2004, pp. 46–47.〕 The AF-12s took the seventh through ninth slots on the A-12 assembly line; these were designated as ''YF-12A'' interceptors.〔Landis and Jenkins 2005, pp. 40–41.〕 The main changes involved modifying the A-12's nose by removing the chines to accommodate the Hughes AN/ASG-18 fire-control radar originally developed for the XF-108, and the addition of the second cockpit for a crew member to operate the fire control radar for the air-to-air missile system. The modifications changed the aircraft's aerodynamics enough to require ventral fins to be mounted under the fuselage and engine nacelles to maintain stability. The four bays previously used to house the A-12's reconnaissance equipment were converted to carry Hughes AIM-47 Falcon (GAR-9) missiles.〔 One bay was used for fire control equipment. The first YF-12A flew on 7 August 1963.〔Green and Swanborough, 1988, p. 350.〕 President Lyndon B. Johnson announced the existence of the aircraft〔McIninch 1996, p. 15.〕 on 24 February 1964.〔Air Force Museum Foundation, 1983, p. 133.〕〔McIninch 1996, p. 14.〕 The YF-12A was announced in part to continue hiding the A-12, its still-secret ancestor; any sightings of CIA/Air Force A-12s based at Area 51 in Nevada could be attributed to the well-publicized Air Force YF-12As based at Edwards Air Force Base in California.〔 On 14 May 1965 the Air Force placed a production order for 93 F-12Bs for its Air Defense Command (ADC).〔Pace 2004, p. 53.〕 However, Secretary of Defense Robert McNamara would not release the funding for three consecutive years due to Vietnam War costs.〔 Updated intelligence placed a lower priority on defense of the continental US, so the F-12B was deemed no longer needed. Then in January 1968, the F-12B program was officially ended.〔Donald 2003, pp. 148, 150.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lockheed YF-12」の詳細全文を読む スポンサード リンク
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