Project Kedlock: the YF‑12 interceptor

Spurred on by the earlier success of his A‑12 design for the CIA, Kelly Johnson discussed the possibility of building a long‑range interceptor version for the Air Force, during a meeting on March 16–17, 1960, with Gen Hal Estes of Air Force Systems Command and Dr Courtland Perkins, the Air Force Secretary for Research and Development. Referred to as the AF‑12, the idea was keenly received and subsequently forwarded to Gen Martin Demler, at Wright‑Patterson AFB, for further discussion and analysis. During late October 1960, Lockheed received a letter of intent for $1 million and was directed to “go forward with Plan 3A” and produce an interceptor version of the A‑12 equipped with the Hughes ASG‑18 Fire Control System (FCS) and the GAR‑9 missile (both radar and missile systems had already been developed for the USAF North American F‑108 Rapier, which had been subsequently canceled on September 23, 1959 due to escalating costs). The program was accorded the classified codename Kedlock, and the seventh A‑12 was nominated to become the AF‑12 prototype.

The modified A‑12 accommodated a fire control system operator in a second cockpit, similar to the M‑21. The forward fuselage chines were cut back to incorporate a radome that housed a 40in‑diameter scanning dish, and four weapons bays were cut into the underside to house the FCS in the forward right bay and a GAR‑9 missile in each of the other three bays. But by June, wind tunnel tests revealed that these modifications had resulted in directional stability problems. To alleviate these, two fixed ventral fins were installed on the underside of each engine nacelle. In addition, a large sideways‑folding fin was mounted at the rear of the aircraft’s centerline. Retraction and extension of the folding fin worked out of phase with the cycling of the landing gear – as the gear retracted, the fin extended and vice versa.

Concurrent to activity on the AF‑12, a two‑seat bomber version of the A‑12, referred to as the RB‑12, was also being studied. A full‑scale mock‑up of the forward fuselage was built and then reviewed by Gen Curtis LeMay and Gen Thomas Power on July 5, 1961; but despite considerable interest, this program would prove to be stillborn.

In total, three AF‑12s were constructed, with the maiden flight of the prototype being conducted by Lockheed test pilot Jim Eastham from Area 51 on August 7, 1963. To draw attention away from the covert CIA A‑12 program, President Lyndon Johnson announced the existence of the “A‑11” at Edwards AFB on February 29, 1963. The “A‑11” title was a deliberate piece of deception engineered by Kelly Johnson; but with the AF‑12 now assigned an official Air Force designation (YF‑12A), this further compounded the confusion!

Test flights of the new interceptor from Edwards AFB continued with increased frequency and confidence and on April 16, 1964, the first missile – now designated AIM‑47 – was ejected in flight. Between March 18, 1965 and September 21, 1966, the three YF‑12As fired a total of seven AIM‑47s. The final mission (G‑20), flown in YF‑12A 60‑6936, successfully intercepted a QB‑47 remotely piloted target drone whilst cruising at Mach 3.2 and an altitude of 74,000ft – the target drone was at sea level!

Aerospace Defense Command officials calculated that 96 F‑12B production aircraft could replace its entire fleet of Convair F‑102 Delta Dagger and F‑106 Delta Dart interceptors and provide protection for the entire United States against incoming Soviet high‑speed, low‑level bombers; but it wasn’t to be. Instead, political shenanigans and a long‑simmering feud over the appropriation of defense funds between Secretary of Defense Robert McNamara and the Air Force resulted in McNamara denying $90 million worth of funds that had been appropriated by Congress to begin F‑12B production. These delaying tactics played out by McNamara eventually paid off and on January 5, 1968, the Skunk Works finally received official notification from the Air Force to close down the F‑12B production line. To seal the fate of future Mach 3 aircraft production, Johnson received a letter from the Air Force dated February 5, 1968, instructing Lockheed to destroy the A‑12/F‑12 tooling, including that used in SR‑71 production. In a later response the designer wrote, “We have proceeded to store such items as are required for producing spare parts at Norton. The large jigs have now been cut up for scrap and we are finishing the clean‑up of the complete area. Ten years from now the country will be very sorry for taking this decision of stopping production on the whole Mach 3 series of aircraft in the USA.”