A newly declassified document shows that, during the Cold War, the U.S. military considered turning Lockheed’s D-21 Tagboard supersonic spy drone into an unmanned strike platform. The plan would have given the U.S. Air Force a high-speed, deep-penetrating, air-launched strike weapon and it’s a capability the service is still interested in acquiring today. In January 1971, John McLucas, then both Undersecretary of the Air Force and Director of the National Reconnaissance Office (NRO), sent a memo to Deputy Defense Secretary David Packard about the armed D-21 proposal. NRO, the very existence of which remained classified until 1992, released this record and nearly 100 other documents related to the Tagboard program as part of its continued transparency efforts, on Mar. 21, 2019.

“With respect to your question about whether TAGBOARD should be considered as a drone/bomber, we have done some investigation and discussed this with the Air Staff and SAC [Strategic Air Command],” McLucas wrote. “I will be glad to do any additional analysis or other work which you might suggest.”

USAF A D-21 drone.

But Tagboard’s origins, and nearly two decades of development and operational activities up to that point, were rooted almost exclusively in intelligence collection. To rewind a bit, after the Soviet Union shot down Gary Powers flying a U-2 Dragon Lady spy plane over their territory in 1960, there was a considerable impetus to develop less vulnerable intelligence gathering assets that could penetrate far into denied areas with limited risk. Lockheed, which had designed and built the U-2, was already in the process of developing a successor, known as the A-12 Oxcart at the time. This aircraft subsequently evolved into the Air Force’s famous SR-71 Blackbird.

Lockheed SR-71s under construction.

The A-12 could fly at over three times the speed of sound at around 90,000 feet, but there were still reservations within the U.S. government about sending any manned aircraft on high-risk missions over hostile countries, such as the Soviet Union. At the same time, NRO was pushing ahead with the first generations of spy satellites, which, at the time, offered a way to spy on these areas with virtual impunity. The problem with early spy satellites was that they could only carry limited amounts of wet film, reducing their capacity to cover large areas and do so over a protracted period of time. In addition, they had limited repositioning flexibility once they entered their orbits. On top of all this, it was a complex process to prepare additional satellites for launch, making it difficult to ensure one was ready to go on short notice in response to new developments.

NRO A graphic describing the general features of the KH-4B Corona spy satellite, which NRO declassified more than a decade ago as part of a separate release of records. Note that this satellite, the first which the United States launched in 1967, still had an average mission life of fewer than 20 days.

So, the U.S. government had sought out additional alternative intelligence gathering platforms that were less vulnerable than manned aircraft, but more flexible than a satellite. The Central Intelligence Agency, which controlled the A-12 fleet, approached Lockheed and its Skunk Works advanced projects division in 1962 to ask for new options. One concept that Skunk Works proposed envisioned using a modified A-12 as a mothership to carry and launch a rocket booster with a small satellite on top into low orbit. You can read more about this project here. Another idea involved a modified A-12 as a launch platform for an air-breathing, high-altitude supersonic unmanned spy drone. CIA passed on this proposal, but NRO picked it up, ultimately giving the project the codename Tagboard. At that time, there were no plans to turn the unmanned aircraft into a strike platform. The delta-wing unmanned aircraft, constructed primarily of titanium, was more than 40 feet long and had a wingspan of 20 feet. A modified Marquardt RJ43 ramjet engine, also found on the CIM-10 Bomarc surface-to-air missile and AQM-60 Kingfisher target drone, could propel the D-21 to speeds over Mach 3 at altitudes of around 100,000 feet – higher than the A-12’s service ceiling.

Lockheed via NRO A declassified technical drawing of the D-21 drone.

Tagboard needed its modified two-seat A-12 motherships, which became known as M-21s, to get it to sufficiently high speed for the ramjet to operate efficiently. After release from the M-21, the drone would fly a pre-programmed route totaling more than 3,000 miles using an automated stellar navigation system, something you can read about more here. The drone carried a single Hycon HR 335 camera that could capture images of areas up to between 14 and 16 miles wide, depending on altitude, as it screamed across enemy territory.

Lockheed via NRO A declassified technical drawing of the M-21 mothership with the D-21 drone on top.

After conducting its mission, its route would take it back out to neutral territory, where it would eject the film canister, which would then deploy a parachute. The D-21 was not reusable and was configured to self-destruct after releasing its payload. A specially modified JC-130 Hercules cargo aircraft would snatch the film out of the air using a complex trapeze before reeling it in inside and transporting it back to base for processing. The Air Force, with the help the CIA and NRO, had devised this concept first in the 1950s to catch falling film pods that spy satellites released. This continued to be the standard practice for retrieving film and other data from satellites until technology had advanced to the point where it was practical to transmit imagery and other information wirelessly straight to a ground station.

USAF A JC-130 Hercules practices a maneuver to catch falling film canisters near Edwards Air Force Base in 1969.