By 1962 Kelly Johnson had done at least a few studies on using the A-12 as a carrier for a QF-104 Starfighter.
The A-12 was the product of Project Oxcart, a secret military program to develop a high-speed, high-altitude reconnaissance aircraft. First flown in 1962, the A-12 was built by Lockheed’s Advanced Development Projects office, now known as Skunk Works. The A-12 was capable of performing sensitive intelligence-gathering missions while flying at speeds over Mach 3, or three times the speed of sound. The Central Intelligence Agency (CIA) used A-12s for surveillance missions until 1968. Later versions, known as the SR-71 Blackbird, served in reconnaissance and test missions for the US Air Force (USAF) and NASA through the 1990s.
As told by Scott Lowther in the book Origins and Evolution Lockheed SR-71 Blackbird, two of the A-12 airframes were built from the beginning for a very different role. As the programme was developed, the CIA became concerned about the risks of sending a manned vehicle — even one as advanced as the A-12 — over enemy territory. The loss of a pilot and advanced technology over ‘denied’ territory could prove not only technologically devastating but also politically embarrassing, as the shootdown of Francis Gary Powers had amply demonstrated. So, they requested that Kelly Johnson and his team study unmanned drones to be launched from the back of the A-12 as an alternative.
By 1962 Johnson had done at least a few studies on using the A-12 as a carrier for a QF-104. There is little more to go on than the simple description of the idea, so it’s uncertain how changed the QF-104 would have been compared to a standard F-104. The diagram included here should be considered wholly provisional. However, at first glance the concept seems feasible enough. But it would be strange to use a more or less stock F-104, capable of reaching about Mach 2 with a ceiling of 50,000ft, launched from an aircraft capable of flying more than 50% higher and faster. It’s entirely possible that the J-79 turbojet would have been replaced by a ramjet, with aerodynamics and structure changed to permit higher speeds and altitudes.
The A-12/QF-104 idea apparently did not grab the CIA’s interest and the AQ-12, an all-new, highly optimized drone, was wanted instead.
The program would see the AQ-12 being launched from the back of an A-12 designated ‘M-21,’ M for ‘Mother’ and 21 being simply a reversal of the 12 to prevent confusion. The AQ-12 was redesignated D-21, D for ‘Daughter.’
On the fourth flight test, the D-21 experienced an “asymmetric unstart” as it passed through the bow wake of the M-21 causing the mothership to pitch up and collide with the D-21 at Mach 3.25. Crewmembers Bill Park and Ray Torick ejected from the M-21, but Torick’s flight suit became ripped and filled with water when he plunged into the ocean where he drowned.
After the accident, the M-21 launch program was cancelled but testers still believed the D-21 would make a valuable reconnaissance vehicle and decided to launch the drone from B-52Hs under a top-secret test program named Tagboard. The new code name for the D-21 project became Senior Bowl.
Under Senior Bowl, D-21s were used on four flights over communist China, but none of these missions fully succeeded. The USAF canceled the program in 1971 and put the remaining D-21s in storage.
Origins and Evolution Lockheed SR-71 Blackbird is published by Mortons Books and is available to order here.
Photo credit: U.S. Air Force and Scott Lowther via Mortons Books