Southern California's lost long-range interceptors, part 2: Lockheed YF-12

The cancellation of the F-108 Rapier in September 1959 was a setback to efforts by the US Air Force to field an advanced long-range interceptor to take on advanced strategic bombers being developed by the USSR, including the Myasishchev M-50 and Tupolev Tu-22. However, the quest by the aircraft industry of southern California to provide the Air Defense Command with a Mach 3 interceptor did not totally die out with the F-108's termination. Not too long after the F-108 program was axed, a revolutionary aircraft of similar speed to the F-108 would come to form the basis for another US effort to acquire a Mach 3 long-range interceptor, this time from Lockheed.

Desktop model of the YF-12 at the Planes of Fame Museum, Chino (photographed by me in 2018)

In 1960, while undertaking development of the A-12 (Archangel-12) spy plane, Lockheed proposed a long-range interceptor variant of the A-12 for the US Air Force under the internal designation AF-12. The AF-12 design was to have provisions for a second crewmember (radar operator), missile bays for folding fin versions of the GAR-9 (later AIM-47) long-range air-to-air missile, and a Hughes ASG-18 fire control search-and-track radar. Pleased with the AF-12 proposal, in October 1960 the US Air Force signed a contract whereby the seventh through ninth A-12s on order (serial numbers 60-6934/6936) would be completed as AF-12s. The CIA assigned the codename KEDLOCK to the AF-12 program, and a mock-up was inspected by Air Force officials in May 1961, after which the AF-12 design was tweaked the following month to include three ventral fins (two below the engine nacelles and a third larger fin below the extreme rear of the fuselage). To accommodate the Hughes ASG-18 fire-control radar, the chines were cut back insofar that they extended to the front of the cockpit, and the nose was now made of plastic composite material that was transparent to radar and resistant to thermal loads expected from Mach 3+ flight. The AF-12 had a length of 101 feet 8 in (30.97 meters), a wingspan of 55 feet 7 in (16.95 meters), a height of 18 feet 6 in (5.64 meters), a wing area of 1,795 square feet (167 square meters), an empty weight of 60,730 lb (27,604 kg), a gross weight of 124,000 lb (56,200 kg), and a maximum takeoff weight of 140,000 lb (63,504 kg).

Select photos of the Lockheed YF-12A in flight 

Construction of the first AF-12 began in August 1962 at the Lockheed factory in Burbank, California, where other A-12s were being manufactured. After the Defense Department introduced the Tri-Service aircraft designation system on September 18, 1962, the AF-12 was officially designated YF-12 as a matter of convenience given its A-12 heritage. The first YF-12A was completed in the first half of 1963 and transported to Area 51 in Groom Lake, Nevada, where it made it first flight on August 7; the second YF-12A aircraft flew for the first time on November 23, 1963, and the third prototype followed suit on March 13, 1964. The YF-12A's existence was publicly disclosed on February 29, 1964 when President Lyndon B. Johnson referred to it as "A-11" at his first nationally televised news conference, and the aircraft was publicly unveiled at Edwards Air Force Base on September 30. For security reasons, LBJ may have chosen to referred to the YF-12A as "A-11" because the Soviets had breached Lockheed and CIA security, even though the A-11 was a fundamentally different design than the YF-12A (Lowther 2021, pp. 99-100). In the meantime, the AIM-47 Falcon was ejected from a YF-12A for the first time on April 16, 1964, and on March 18, 1965 the YF-12A scored its first kill when an AIM-47 hit an aerial  target 36.2 miles (58.26 km) away. On May 1, 1965, the first and third YF-12As set speed and altitude records of 2,070 miles per hour (3,331.505 km/h) and 80,258 feet (24,462.60 meters) respectively, and four months later, on September 28, the first YF-12A fired an AIM-47 at a speech of Mach 3.2 at an altitude of 75,000 feet (22,860 meters), intercepting a JQB-47E target drone 32.2 miles (51.8 km) away at 500 feet (150 meters). In all, 13 missile firings were conducted from the YF-12A up to 1966.

Forward fuselage mock-up of the Lockheed F-12B, the proposed production F-12

The USAF's Air Defense Command was quite impressed by test flights of the YF-12A, and May 14, 1965 it placed a production order for 93 F-12Bs. The F-12B was similar to the YF-12A but differed in utilizing the nose chines of the A-12 and SR-71 but also eliminating the central large stabilizing fin below the rear fuselage, not to mention that the underside of the forward fuselage was flattened and the tail of the rear fuselage extended as in the SR-71. Instead of using ejectors to toss the AIM-47s from the internal weapons bays, the F-12B would have used deployable trapeze launch rails that could deploy the missiles in a substantially nose-down altitude. Plans called for spreading out the F-12B fleet to different Air Force bases, with three squadrons of 16 F-12Bs each sent to bases in the northeast US, and three squadrons of 16 aircraft deployed on the west coast of the US. However, US Secretary of Defense Robert McNamara did not support development of the F-12B, and due to Vietnam War cost and a lower priority placed by updated intelligence analysts upon defense of the continental US, the F-12B program was cancelled in January 1968. Not too long before the F-12B's cancellation, Lockheed had also looked into a fighter-bomber version of the F-12, unofficially called FB-12 by the company, which resembled the SR-71 and would carried either four AGM-69 nuclear-armed land attack missiles, two AGM-69s and two AIM-7 Sparrow air-to-air missiles, four AIM-7s, three AIM-7s and one M61 Vulcan machine gun, four AIM-47s, or three AIM-47s and one M61. However, the FB-12 went no further than the drawing board because the FB-111 and F-15 would soon be developed to fulfill the FB-12's intended air-to-air and air-to-ground roles. In the meantime, the first YF-12A (serial number 60-6934) suffered a landing mishap that caused the forward fuselage to be damaged beyond repair, leaving the remainder of the first YF-12A to be mated with a static test SR-71 airframe to create the SR-71C two-seat trainer. The second and third YF-12A later were transferred to NASA in 1969 for scientific missions ranging from sonic boom tests to high-altitude air sampling; serial number 60-6936 was lost in a crash near Edwards Air Force Base on June 24, 1971 after an in-flight fire, but both pilots ejected safely, while the sole remaining YF-12A continued serving NASA until November 17, 1979, when it was flown to the US Air Force Museum at Wright-Patterson Air Force Base in Dayton, Ohio. (NASA acquired SR-71 serial number 61-7951 in 1971 for aerodynamic research purposes after the crash of the third YF-12A and assigned it the bogus designation YF-12C and the fair serial number 60-6937 due to the secrecy surrounding the SR-71, operating this aircraft until December 1978, but that is another story.)

Although the F-108 Rapier was canceled without ever reaching the hardware phase and the F-12 almost made it into production when the Defense Department canceled F-12 production plans after deciding that defense of the continental US wasn't too important, some legacies of the F-108 and F-12 programs would find their way into future jet fighters. For example, the AIM-47 Falcon designed to be carried by the F-108 and F-12 would form the basis of the AIM-54 Phoenix, the chief armament of the US Navy's F-14 Tomcat, while the ASG-18 radar was later developed into the more advanced AWG-9 and APG-71 all-weather radars that equipped the F-14. Today, the F-15 Eagle and F-22 Raptor utilize the long-range air-to-air combat role envisaged for both the F-108 and F-12 in tandem with the air superiority role for which they are primarily designed.

References:

Jenkins, D.R., and Landis, T.R., 2008. Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, MN: Specialty Press.

Landis, T.R., and Jenkins, D.R., 2005. Lockheed Blackbirds (Warbird Tech Series, Volume 10), Revised edition. Minneapolis, MN: Specialty Press. 

Lowther, S., 2021. Lockheed SR-71 Blackbird - Origins and Evolution. Horncastle, UK: Tempest Books.