|The D-21 mounted on the back of the M-21. Note the intake cover on the drone, which was used on early flights.|
|Role||High-altitude reconnaissance aircraft and drone|
|First flight||22 December 1964|
|Primary user||Central Intelligence Agency|
|Number built||M-21: 2, D-21A/B: 38|
|Developed from||Lockheed A-12|
The Lockheed D-21 was a Mach 3+ reconnaissance drone. The drone was originally designed to be launched off the back of its A-12-based M-21 aircraft. Development began in October 1962. Originally known by the Lockheed designation Q-12, it was intended for reconnaissance missions deep into enemy airspace. The D-21 was designed to carry a single high-resolution photographic camera over a pre-programmed path, then release the camera module into the air for retrieval, followed by the drone's self-destruct.
In the early 1960s, Lockheed had developed the Mach 3 A-12 reconnaissance aircraft for the CIA. After the downing of Gary Powers' U-2 in 1960, concepts for drones were proposed. Kelly Johnson, in charge of Lockheed's secret Skunk Works that had built the A-12, thought the A-12 itself would be too big and complicated to make a useful drone, but felt that the design and technology could be used to build a smaller aircraft that could perform the same mission. In October 1962, the CIA and US Air Force instructed Lockheed Skunk Works to study a high-speed, high-altitude drone concept. The Q-12's design had a double-delta wing similar to the A-12's outer wing design. The Q-12 was to be air-launched from the back of an A-12, and used key technology from the A-12 project, including titanium construction.
Kelly Johnson wanted to power the Q-12 with a ramjet engine built by Marquardt for the Boeing BOMARC long-range surface-to-air missile. Marquardt's plant was close to Lockheed's, helping ensure security, and the two companies had already collaborated on several programs. Marquardt engineers indicated that the BOMARC ramjet could be used, though the engine, ultimately designated the RJ43-MA-11, needed some work, since it wasn't designed to burn for much longer than it took a BOMARC to hit a target a few hundred kilometers away. In contrast, the Q-12's engine was to operate for at least an hour and a half, much longer than any ramjet at that time. The engine also needed to be modified to burn the same JP-7 fuel used by the mother plane.
A mockup of the Q-12 was ready by 7 December 1962. Radar tests indicated that it had an extremely low radar cross section. Wind tunnel tests also indicated the design was on the right track. However, the CIA was not enthusiastic about the Q-12, mostly because the agency was overextended at the time with U-2 missions, getting the A-12 up to speed, and covert operations in Southeast Asia. In contrast, the Air Force was interested in the Q-12 as both a reconnaissance platform and a cruise missile, and the CIA finally decided to work with the USAF to develop the new drone. Lockheed was awarded a contract in March 1963 for full-scale development of the Q-12.
The reconnaissance payload and guidance systems were carried in a "Q-bay" about 6 feet (1.9 m) long. These systems were built into a module that plugged neatly into the bay and was known as a "hatch". As per the original design concept, the hatch would be ejected at the end of the mission, and the aircraft would then blow itself up with a self-destruct charge. The hatch would be snagged out of the air by a C-130 Hercules, a technique that had been refined by the Air Force to recover film canisters from reconnaissance satellites.
In late 1963, the project was named "Tagboard"; the Q-12 was re-designated D-21 while the A-12 version became M-21 (D- for "daughter" and M- for "mother"). Two production slots from the original 18 A-12 units were designated for the M-21, serial numbers 60-6940, and -6941. The M-21 was a two-seat version of the A-12, with a pylon on the fuselage centerline between the tailfins to carry the drone in a nose-up attitude. A periscope allowed the back-seater, or Launch Control Operator (LCO), to observe the D-21. Two M-21s were built, along with an initial batch of seven D-21s for test flights.
The M-21/D-21 program was canceled after an in-flight accident in July 1966. After this the D-21 drone was modified to the D-21B version to add a booster rocket and mount on an underwing pylon on B-52Hs. After flight testing and four operational launches, the B-52H/D-21B program was ended in July 1971.
The M-21/D-21 combination began captive flight-testing on 22 December 1964, continuing through 1965. Aerodynamic covers that were in place over the intake and exhaust were removed after the first few tests, as it was unable to drop them at Mach 3 without damaging the M-21 and/or D-21. Increased drag caused by the removal was overcome by using the D-21's ramjet as a third engine, drawing fuel from the M-21's tanks until the drone was released.
The first launch of the D-21 from the back of the M-21 occurred successfully on March 5, 1966. The release was successful, though the drone hovered above the back of the M-21 for a few seconds, which seemed to one of the flight crew like "two hours". Kelly Johnson called it "the most dangerous maneuver we have ever been involved in, in any airplane I have ever worked on." The D-21 itself crashed after a flight of a few hundred kilometers. As a result, the CIA and the Air Force were still not very enthusiastic about the program. Kelly Johnson conferred with Air Force officials to see what he could do to tune the project more closely to the service's needs. Among other things, Johnson suggested launching the D-21 from a larger aircraft and using a solid rocket booster to get the drone up to speed.
A second successful launch took place on 27 April 1966, with the D-21 reaching its operational altitude of 90,000 feet (27,400 m) and speed in excess of Mach 3.3, though it was lost due to a system failure after a flight of over 1,200 nmi (2,200 km). This was regarded as very satisfactory progress. The successful tests sharpened the interest of the program's government backers, and by the end of the month a contract for 15 more D-21s had been placed. A third successful flight took place on 16 June 1966, with the D-21 flying through its complete mission, though the hatch wasn't released due to an electronics failure.
However, the fourth and final launch a month later on July 30 ended in disaster. The D-21 struck the M-21's tail immediately after separation, destroying both aircraft. The two crewmen ejected safely and landed at sea. The pilot, Bill Park, survived, but the LCO, Ray Torick, drowned when his pressure suit leaked. As a result, Kelly Johnson immediately ended launches from the M-21. However, he felt that the B-52 launch scheme was still practical, and the D-21 program remained alive and well.
The modified drone was designated D-21B (although there was no -21A version) and all D-21s on order in mid-1966 were completed as D-21Bs. Two B-52Hs were modified to carry two drones each and were given two large underwing pylons to carry the drones, replacing the smaller pylons used for the B-52's AGM-28 Hound Dog cruise missiles. Two independent LCO stations were added at the rear of the bomber's flight deck, along with command and telemetry systems; a stellar navigation system to ensure that the drones were launched from well-defined coordinates to reduce flight guidance error; and a temperature control system to keep the drones at a stable temperature before launch.The B-52Hs could communicate with the D-21Bs, which had improved remote control links that remained active up to 10 minutes into the mission.
The booster was a solid-fuel rocket with a length of 44 feet 4 inches (13.5 m) and a weight of 13,290 pounds (6.025 tonnes), making it longer and heavier than the drone itself. The booster had a single small tailfin on the bottom to ensure that it flew straight. The tailfin folded to ensure ground clearance. The booster had a burn time of about a minute and a half, and a thrust of 27,300 pounds (121 kN).
Initial testing began in September 1967 and went on until July 1969. The first attempted launch of a D-21B was on 28 September 1967, but the drone accidentally fell off the B-52's pylon. Its booster fired but the D-21B went straight into the ground. Kelly Johnson called the incident "very embarrassing". Three more launches were performed from November 1967 through January 1968. None were completely successful, so Johnson ordered his team to conduct a thorough review before renewing launch attempts. The next launch was on 30 April 1968, and was also a failure. The Lockheed engineers went back to the drawing board once more, and on 16 June 1968 they were rewarded with a completely successful flight. The D-21B flew a test mission at the specified altitude and course over its full range, and the hatch was recovered successfully, though it didn't have a camera payload.
The troubles were not over yet, however. The next two launches were failures, followed by another successful flight in December. A launch near Hawaii in February 1969 to simulate an actual operational flight was a failure as well, but the next two flights, in May and July, were both successes.
Four operational missions took place under the name SENIOR BOWL, from November 9, 1969 to March 20, 1971, all over the People's Republic of China to spy on the Lop Nor nuclear test site. On the first mission, the Chinese never spotted the stealthy drone, but it disappeared and was not recovered. Once again, the Lockheed engineers went back to the drawing board. Another test flight was conducted on 20 February 1970, and was successful. However, the second operational mission was not until 16 December 1970. The D-21B made it all the way to Lop Nor and back to the recovery point, but though the hatch was dropped as planned, it did not deploy its parachute and was destroyed on impact.
The third operational flight, on 4 March 1971, was even more frustrating. Once again, the D-21B traveled to Lop Nor and back, and properly discarded the hatch. The hatch deployed its parachute, but the midair recovery failed, and a destroyer that tried to retrieve the hatch from the sea ran it down. The hatch sank and was lost. The fourth, and last, flight of the D-21B was on 20 March 1971. It was lost over China on the outbound leg. According to recent information out of China, it mulfunctioned and crashed in a forest. It is said to be largely intact and wreckage collected by the Chinese military.
In July 1971, the D-21B program was cancelled, due to a combination of the poor level of success and the introduction of a new generation of photo reconnaissance satellites, as well as President Richard Nixon's rapprochement with China.
When Ben Rich, Kelly Johnson's successor at the Skunk Works, visited Russia in the 1990s after the fall of the USSR, a contact gave him a package that contained parts of the D-21 that had disappeared on the first operational flight. It had crashed in Siberia. The Soviets had apparently been puzzled as to what it was, but it appears that they also obtained the wreckage of the D-21 lost on the fourth operational flight. The Tupolev design bureau reverse-engineered the wreck and came up with plans for a Soviet copy, named the "Voron (Raven)", but it was never built.
In the end, 38 D-21/D-21B drones were built with 21 expended. The other 17 were put in mothballs at the Davis-Monthan Air Force Base "boneyard" near Tucson, Arizona and redesignated as GTD-21B. Since the base is open to the public, the exotic D-21s were eventually spotted and photographed, leading to speculation as to their nature, speculation that was inflamed by misinformation from the Air Force. For example, they were described as test machines used in development of the A-12 / SR-71.
The mothballed drones were passed off to NASA, which took four. In the late 1990s, NASA considered using their D-21s to test a hybrid "rocket-based combined cycle (RBCC)" engine, which operates as a ramjet or rocket, depending on its flight regime. This idea was abandoned, with NASA preferring to use a derivative of the agency's X-43A hypersonic test vehicle for the experiments. Other D-21s have been released to museums for display.
|Serial number||Model||Location or fate|
|60-6940||M-21||Museum of Flight, Seattle, WA|
|60-6941||M-21||Lost, 30 July 1966|