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The D-21 had originally been designed for launch from the trisonic Lockheed A-12 but difficulties (culminating in a fatal accident) forced Lockheed to find a new carrier.
The Lockheed D-21 was a highly-advanced, remotely piloted aircraft (RPA) designed to carry out high-speed, high-altitude strategic reconnaissance missions over hostile territory. It was powered by a ramjet. The D-21 had originally been designed for launch from the trisonic Lockheed A-12 (developed alongside the SR-71), but difficulties (culminating in a fatal accident) forced Lockheed to find a new carrier.
Two H-model ‘Buffs’ (B-52H-140-BW 60-0021 and B-52H-150-BW 60-0036) were converted to carry the D-21B reconnaissance drone under Operation Senior Bowl, funded by the CIA. The D-21 drone was modified to D-21B standards, with a 90-second solid fuel rocket booster for accelerating the drone to its 80,000 ft operating altitude and Mach 3 operating speed.
As explained by Jon Lake in his book B-52 Stratofortress Units in Combat 1965-73, the first of the two launch aircraft (B-52H-140-BW 60-0021) was sent to Palmdale on Dec. 12, 1966, where it was fitted with massive inboard underwing pylons from which the D-21s could be suspended. The gunner and EWO positions in the cockpit were also replaced by new Launch Control Officer stations. The aircraft were fitted with camera ports in the fuselage sides and in the launch pylons to allow the launch to be filmed, but the normal tail armament was retained, contrary to some reports.
After training at Groom Lake (‘The Ranch’) with a unit simply known as A Flight, the two D-21 carriers were operated from late 1968 by the 4200th Support Squadron (SS) at Beale Air Force Base (AFB), being kept on a virtual alert status with two ‘birds’ on each B-52H. After launch from Beale, the B-52Hs flew to Andersen, Hickam or Kadena AFBs, from where operational missions were mounted. Sorties were flown on Nov. 9, 1969, Dec. 16, 1970, Mar. 4, 1971 and Mar. 20, 1971. The first and last drones were lost over enemy territory, and the second and third missions were fruitless because the vital palletised camera hatches containing the mission film were not recovered after being ejected from the drones. All the D-21Bs launched from 4200th SS B-52Hs were dropped from the starboard pylon, with the port station carrying the back-up D-21B, which was never used operationally. The programme was terminated on Jul. 23, 1971.
The aircraft wore standard early style SIOP camouflage, with painted radomes, although 60-0036 featured a non-standard white-painted cockpit roof to reflect the bright sun at high altitude. Both ‘Buffs’ remain operational today and in 2017 60-0036 received a special “Tagboard Flyer” nose art by famous aviation artist Mike Machat to celebrate the 50th anniversary of D-21 supersonic reconnaissance drone.
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