The YF-12 "Blackbird" was an experimental fighter-interceptor version of the Lockheed A-12 aircraft. In Air Force flight tests on May 1, 1965, the YF-12 set a speed record of 2,070.101 miles per hour and an altitude record of 80,258 feet. First publicly displayed at Edwards Air Force Base, California, in 1964, the YF-12 was never adopted by the military as an operational aircraft. It was, however, associated with the SR-71 Blackbird reconnaissance plane.
A planned operational version of the YF-12A interceptor, designated F-12B, failed to materialize as Secretary of Defense Robert McNamara ultimately cancelled the program in a cost-cutting measure. As a consequence, on 29 December 1967, Air Force officials instructed Lockheed to terminate F-12B development. The YF-12A program ended in February 1968, and the aircraft joined the A-12 fleet in storage. There they remained until the National Aeronautics and Space Administration (NASA) reached an agreement with the Air Force for a joint research program. Beginning in 1969, NASA operated two YF-12A aircraft and one SR-71A (temporarily designated YF-12C for political reasons). The joint NASA-Air Force program continued for ten years.
In 1959, Lockheed began work on the design of a long-range, high-altitude plane, then known as the A-11. It was a Cold War project. Heading the project team was Clarence "Kelly" Johnson, Lockheed's Vice President for Advanced Development Projects. Kelly Johnson had previously led the development of the U-2 spy plane. The plane's existence remained secret for five years, but the tantalizingly small amount of information sparked a collection of very well done "scientific intelligence" articles by several trade and technical journals on the possible planform of the aircraft, its ultimate capabilities, and its mission. None of these articles put much stock in the notion of interception as the primary mission for the A-11 because of its lack of maneuverability at very high speed; most believed it was a spy plane to replace the U-2.
Five years after work began on the A-12, on February 29, 1964, President Lyndon Johnson told reporters that the aircraft (by that time modified to the A-12 production version with a reduced radar cross section) had attained speeds of over 2,000 mph and altitudes of more than 70,000 feet in tests at Edwards Air Force Base.
The MX1554 "Ultimate Interceptor, 1954" produced the Convair F-102 that fell far short of the planned speed, altitude, and range performance. It could only fly at 677 Knots at 35,000 feet, with a maximum ceiling of 51,800 feet and 566 nautical mile combat radius. While the F-102 and its improved area-rule follow-on F-106 served as "interim interceptors," the Air Force developed further requirements for a long range interceptor. These long range interceptor requirements, first developed in April 1953, were rewritten in July 1955 and November 1956, after several attempts failed to get an acceptable proposal from competing airframe contractors.
The Air Force sought an interceptor to counter the perceived 1960 bomber threats of Mach 2.0 speed at 61,000 feet, and the revised 1963 bomber threats of Mach 2.2 to 2.7 speed at 65,000 feet. Design studies to satisfy these requirements began in 1953 at Air Research and Development Command and in industry with the MX1554 designed to achieve a Mach 4.5, 150,000 pound gross takeoff weight aircraft, but the aircraft appeared to be beyond the state of the art. So another round of design studies attempted to meet the 1955 LRI (long range interceptor) requirements. These studies called for an aircraft with a cruise speed of Mach 1.7 at 60,000 feet and combat speed of Mach 2.5 at 63,000 feet, with a gross takeoff weight of 98,500 pounds. But this aircraft would have had only marginal capability against the postulated 1963 bomber threat.
A subsequent design competition in 1955 between Lockheed, Northrop, and North American was little better than previous ones, but North American came closest to meeting the goals. North American Aviation's letter contract of 06 June 1956 called for a long range interceptor that could operate at 70,000 feet with a combat speed of at least Mach 3. The all-weather interceptor aircraft was to have two engines, two crewmen, and at least two internally carried nuclear or conventional mir-to-air missiles. This Weapon System 202 configuration sported a single vertical tail and large delta wing, and was adopted in 1958 after considering iterations with as many as three vertical tails and a large canard.
In 1960, toward the end of the heyday of the "Century Series" fighter aircraft, Weapon System 202, renamed the XF-108 Rapier interceptor, promised to provide the Air Force with a Mach 3 cruise speed and 1,000 nautical mile range as a companion to the proposed B-70 supersonic bomber. The XF-108 design evolved to meet all of the expected Soviet bomber threats of the early 1960s. But intelligence sources eventually proved a serious Soviet bomber threat did not exist. On 23 September 1959 the Air Force canceled F-108 development.
The Lockheed A-12 family, known as the Blackbirds, were designed by Clarence "Kelly" Johnson. They were constructed mostly of titanium to withstand aerodynamic heating. Fueled by JP-7, the Blackbirds were capable of cruising at Mach 3.2 and attaining altitudes in excess of 80,000 feet. The first version, a CIA reconnaissance aircraft that first flew in April 1962 was called the A-12. An interceptor version was developed in 1963 under the designation YF-12A. A USAF reconnaissance variant, called the SR-71, was first flown in 1964. The A-12 and SR-71 designs included leading and trailing edges made of high-temperature fiberglass-asbestos laminates.
The YF-12A represented a complete breaK with earlier American concepts for interceptors. No longer was maneuverability the important issue; speed and tremendous range were key to the concept of intercepting supersonic or even subsonic bombers. With its long range, supersonic speed, and sophisticated avionics, the targeting information or that supplied by any other source, the F-12 could streak to the target and and knock it out with its high-speed, high-maneuverability missiles. The F-12's 3,500 to 4,000 mile range, fire control and armament allowed it to cover the same territory as an estimated nine F-106s. This 100 foot long "fighter" with a 50 foot wingspan clearly differed from earlier machines.
The Johnson Administration considered improvement in defense against manned bomber attack in order to preclude the Soviets from undercutting the Nike-X defense. The investment cost (including R&D) was estimated at about $1.5 to $2.4 billion and would provide for a small force of F-111 or F-12 type interceptors (e.g., 48 F-111s or 32 F-12s) and about 42 aircraft warning and control aircraft (AWACS). With the introduction of these new types of aircraft, the US might have been able to phase out most of the present interceptor aircraft and a large part of the ground-based aircraft warning and control network, thus producing an actual saving in operating costs over the longer term.
The F-12 and F-111 interceptors, equipped with the improved ASG-18/AIM-47 fire control and missile systems, and used with an effective Airborne Warning and Control System (AWACS), would be better than the existing force in operating from degraded bases, countering concentrated bomber attacks, operating independently of a vulnerable fixed ground environment, and dealing with bombers attacking at low-altitude or carrying air-to-surface missiles. With strategic warning it was estimated that 32 UE F-12s or 48 UE stretched F-111As could achieve the same number kills before weapons release as the current force which had a 10 year cost of $3.0 billion. The 10 year systems cost for the 32 UE F-12 force had increased by 1966 from the previously estimated $1.9 billion to $2.9 billion. Estimates for the F-111 force remained at $1.5 billion. The F-111 force therefore appeared substantially more efficient than the F-12s against the currently projected threat. Supplementary calculations indicated that it was comparable in efficiency to the F-12 force against possible future threats.
The Air Force YF-12 flight test program lasted until 1966 at Edwards. The team of Col. Robert L. Stephens and Lt. Col. Daniel Andre took the plane to the record altitude and speed. Secretary of Defense Robert McNamara chose in 1966 to upgrade the F-106 instead of developing the F-12, and deferred deployment of SAM-D, a continental air defense system. The F-12 development program was reoriented in FY 67 and FY 68 to include further design studies for the F-111 interceptor, cost studies, and adaptation of the Navy AWG-9 fire control system for ADC use, using the YF-12 as a test bed.
Usurped by a demand for its successor's capabilities, the experimental YF-12s were essentially shelved until 1969, when two of them were deployed as research vehicles at the NASA Flight Research Center.
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