The D-21B overflight missions were code-named "Senior Bowl."
The first China overflight by a D-21B was made on November 9, 1969.
The B-52H, loaded with two D-21Bs, took off from Beale in the predawn hours and flew west. After twelve hours in the air, it was refueled by a tanker. The B-52H reached the launch point after fourteen hours. This was outside the Chinese early-warning radar network. Article 517 was successfully launched and headed toward China. Its target was the nuclear test site at Lop Nor. The guidance system had all the checkpoints programmed into it.
Once the target was reached, the D-21 was to repeat the maneuvers in reverse order to return to the recovery area. After the telemetry was shut off, however, Article 517 just disappeared. The Chinese never detected it, but Article 517 never reached the recovery zone.[325]
Following the loss, Johnson had the guidance system reprogrammed. This allowed the D-21B to miss a checkpoint and still be able to go on to the next. Inability to do this was the suspected cause of 517's disappearance.[326]
In the wake of the loss, it was decided to fly another test mission. This was made on February 20, 1970, with Article 521. It flew a Captain Hook mission with a total distance of 2,969 nautical miles. It reached an altitude of over 95,000 feet. It followed the programmed flight path within two or three miles. The hatch was recovered, and the photos were good. Lockheed was told to be ready for a second operational mission in March 1970. As events turned out, political considerations caused the program to be idle for nearly a year. It was not until late 1970 that a second "hot" mission was authorized.
The launch was made on December 16, 1970. Article 523 flew the mission to Lop Nor successfully. Over the recovery zone, the hatch separated, but the parachute failed to open and it was destroyed on impact. Several more months went by before authorization was given for additional flights.
The third operational flight was launched on March 4, 1971. The flight of Article 526 was successful, but the attempt to recover the hatch ran into problems. The midair recovery was unsuccessful, and the parachute was damaged. The hatch splashed down, and a U.S. Navy destroyer headed toward the floating payload. During the recovery, the ship "keelhauled" the hatch and it sank. Another ship spotted the floating Article 526 airframe, but was unable to get a cable around it before the D-21B sank.
The fourth, and what proved to be the last, D-21B overflight was made on March 20, 1971. Article 527 flew 1,900 miles into Chinese airspace, but was lost on the final segment of the route, over a very heavily defended area. Published accounts do not indicate if it was lost to Chinese air defenses or due to a malfunction.[327]
THE END OF TAGBOARD
On July 15, 1971, Kelly Johnson received a wire canceling the D-21B
program. The remaining drones were transferred from Beale Air Force Base by a C-5A and placed in dead storage. The tooling used to build the D-21Bs was ordered destroyed. On July 23, Johnson went to Beale to hold a final farewell to mark the disbanding of the 4200th Test Wing. He concluded by saying, "The remarkable part of the program was not that we lost a few birds due to insufficient launches to develop reliability, but rather that we were able to obtain such a high degree of performance with such low cost compared to any other system."[328]
In all, thirty-eight D-21s had been built between 1964 and 1969 (Articles 501 to 538). Of these, twenty-one were flown — four in the M-21 launches, thirteen in B-52H test missions, and four in the overflights. Although two operational D-21Bs were able to reach the recovery zone, no photos were recovered.
Like the A-12 Oxcart, the D-21B Tagboard drones remained a Black airplane, even in retirement. Their existence was not suspected until August 1976, when the first group was placed in storage at the Davis-Monthan Air Force Base Military Storage and Disposition Center. A second group arrived in 1977.[329] The seventeen survivors were Articles 502, 510, 513, 522, 524, 525, and 528–538. They were labeled "GTD-21Bs" (GT stood for ground training). Davis-Monthan is an open base, with public tours of the storage area, so the odd-looking drones were soon spotted and photos began appearing in magazines.[330]
The early reports about the D-21Bs underline how elusive the facts about a Black aircraft can be. The early stories speculated that they had been
"proof-of-concept" test vehicles for the A-ll, that they had been an interim reconnaissance aircraft, used until the SR-71 was operational, and that they had been carried under the belly of the A-11/YF-12A.[331]
It was not until 1982 that a single photo each of the D-21/M-21 and D-21B/B-52H combinations were released. By the mid-1980s, more substantial information was available. The details of the loss of Article 135 were published. The accounts also said that "fewer than five" overflights were made, and that one camera package had been lost during an ocean recovery.[332] The B-52H portion of the Tagboard program remained a blank — it was not clear what year the test launches began nor when the overflights were made. Performance of the D-21 was also not clear. Published accounts gave estimates as high as Mach 4 and 100,000 feet. The published range varied between 1,250 and 10,000 miles.[333]
In 1993, a film entitled "Kelly's Way" was produced for the Edwards Air Force Base Flight Test Museum. It included shots of the D-21 being loaded on the M-21, in-flight shots, and film of two successful D-21 launches.
There was no footage of the B-52 launches.
It was not until publication of Jay Miller's book, Lockheed's Skunk Works: The First Fifty Years, in late 1993 that the details were finally released. Miller's book used Kelly Johnson's own logs and official documents to tell the story of the "Blackest" of the Blackbird family. A year later, Ben Rich's book, Skunk Works, gave a personal account of the Tagboard.
That same year, the surviving D-21Bs were released to museums. The Air Force Museum at Wright-Patterson Air Force Base received one, as did the museum at Dover Air Force Base, and the Pima County Air Museum.[334]
Another was particularly appropriate. After the M-21 program was canceled, Article 134 was placed in storage. When the A-12s and SR-71s were sent to museums, Article 134 was given to the Seattle Museum of Flight. It was still in the original silver and black finish, but the pylon had been removed. When the D-21Bs were released, museum volunteers built a new pylon. D-21B Article 510 was then mounted atop Article 134. On January 22, 1994, the new display was opened.[335]
NASA also saw the possibilities of the D-21Bs as test aircraft. The Ames-Dryden Flight Research Center was able to get four of them, Articles 513, 525, 529, and 537. No test program had been determined, but the opportunity to acquire such a vehicle was too good to pass up. One obvious program would be testing of scramjet engines, similar to those planned for the X-30. The launch would be made from one of NASA's SR-71s. It was felt that the unstart problem that had caused the fatal crash had been solved.
Test instrumentation would replace the camera package. As with the earlier mission profile, the D-21B would be lost at the end of the flight. Any such NASA D-21B flight program would be made a quarter century after the last operational mission. In the meantime, D-21B Article 525 was loaned by NASA to Blackbird Park, where it joined the prototype A-12 and an SR-71 on display.
THE TAGBOARD ASSESSED
The D-21B Tagboard was the ultimate expression of the Black reconnaissance aircraft. The end of the D-21 program brought to a close an era of Black airplane development. The first Black airplanes, the XP-59A and P-80, had been tactical fighters. Starting in the early 1950s, the emphasis shifted to reconnaissance aircraft. The following two decades saw the X-16, U-2, Sun Tan, A-12, 147, 154, and, finally, the D-21.
On the surface, the Tagboard program was cut short by President Nixon's ending of China overflights. As with the Model 154, there was also a deeper reason. The cancellation of the D-21B program was not only the result of changing politics, but also a changing reconnaissance situation.
On June 15, 1971—one month before the D-21B program ended — the first Big Bird reconnaissance satellite was orbited. It was built around
a large telescope and had a resolution of six inches from over 100 miles high.
Improved Big Birds would operate for as long as 275 days.[336] Johnson had long realized the effect satellites would have. In 1959, when the A-12 project was just getting started, he asked the CIA whether there would be one round of aircraft development or two before the satellites took over.
Both agreed there would be only one.[337] This proved accurate — while the SR-71 served for a quarter of a century, the A-12 and D-21 both had brief operational lives.
The D-21 Tagboard was as challenging as anything undertaken by the Skunk Works. The development problems were not unusual, given the complexity of the D-21's mission pfotiTe. The development program "was more akin to that of a missile than an aircraft. Like a missile, each D-21 would be lost at the end of the flight — whether it succeeded or failed. All that Lockheed had to go on to determine the cause of any problems was the telemetry. Development of the early missiles was a prolonged process.
GHOST
In February 1986, D-21B Article 517 finally came home. After the guidance system malfunctioned on the first overflight, it had kept going and reached Siberia before self-destructing. The shattered debris rained down from the sky. One of the pieces, a panel from the engine mount, was found by a shepherd, who turned it over to Soviet authorities. Seventeen years after the November morning it was launched, a CIA official walked into Ben Rich's office with the panel. Rich, now head of the Skunk Works after Kelly Johnson's retirement, asked where he had gotten it. The CIA official laughed and said, "Believe it or not, I got it as a Christmas gift from a Soviet KGB agent." The panel, composed of radar-absorbing material, looked as if it had just been made.[338]
As they talked, another Dark Eagle was being built in the same hangar that had seen production of the D-21s. It did not have the thundering speed of the D-21; in fact, this new plane was a subsonic attack aircraft. Unlike the sleek, manta ray shape of the D-21, the new Dark Eagle was angular. It had a form that was a violation of every aerodynamic principle built into airplanes since the Wright Brothers. This strange shape, crafted with the utmost care, had only one virtue.
It was invisible.
CHAPTER 7
The Dark Eagles of Dreamland
The Have Blue Stealth Aircraft
I conceal my tracks so that none can discern them; I keep silence so that none can hear me.
Sun Tzu ca. 400 B.C.
A common thread running through the history of the postwar Black airplanes was the quest for a reduced radar cross section. It was hoped that the U-2 would fly so high it would be difficult to pick up on radar. Tests over the United States seemed to justify this hope, but once overflights began, the Soviets had no major difficulties tracking it. Attempts were made to reduce the U-2s' detectability, but these proved ineffective.
Based on this experience, Kelly Johnson realized the A-12 would have to be designed from the start for a reduced radar cross section. The important word was reduced—the North Vietnamese and Chinese were able to detect the A-12s. Taken together, the A-12s' speed, height, and reduced radar return made them unstoppable.
With the Ryan drones, both approaches were taken. The Model 147 Lightning Bug drones were modified with radar-absorbing blankets. This made the former target drones difficult to shoot down, as the Chinese and North Vietnamese soon learned. With the advanced Model 154, a reduced radar cross section was built in.
In all these cases, however, the reduced radar cross section was only one of the design considerations. The maximum possible altitude was the driving requirement in the design of the Black reconnaissance airplanes.
But by the early 1970s, a reduced radar cross section became the dominant consideration in the design of new aircraft. This became known as "stealth."
A PREHISTORY OF STEALTH
The first attempt to build an "invisible" airplane was made in 1912.
Petrocz von Petroczy, an officer with the Austro-Hungarian air service, covered a Taube with clear sheets of a celluloid material called Emaillit.
The theory was that a transparent covering would make the plane harder to see and hit with ground fire compared to a fabric-covered plane silhouetted against the sky. The Taube was test flown in May and June 1912.
Flight magazine reported that the plane was "unable to be located by those present on the ground when flying at an altitude of between 900 and 1,200 feet… [At 700 feet] only the framework is dimly visible and this and the outline of the motor and pilot and passenger present so small an area for rifle or gun fire, that… accurate aiming at such surfaces becomes nearly impossible."
It was the Germans who soon took the lead. An engineer named Anton Knubel built two monoplanes with clear coverings in 1913-14. The second of the planes had its framework painted a blue gray color to make it even harder to see against the sky. In August 1914, World War I started. In 1915, Knubel built a biplane to test its military applications. Unfortunately, Knubel was killed in a crash of the plane on September 8, 1915.
The idea was seen as having promise, and three Fokker E III fighters were delivered in the summer of 1916, covered with Cellon. Unlike celluloid, it did not burn or shatter. Cellon had found wide use in the automotive industry as a glass substitute. Cellon was soaked in water to expand the sheets. It was then attached to the plane's framework and allowed to dry to a taut finish. The material was called D-Bespannung (Durchsichtige Bespannung or "transparent material under tension").
The trio of E III fighters appear to have seen limited combat. On July 9, 1916, the No. 16 Squadron of the British Royal Flying Corps reported that "a transparent German aeroplane marked with red crosses was pursued by French machines in the Somme area." Several more German aircraft were tested with the Cellon coating. These included four observation-light bombers: an Albatros B II, an Aviatik B, an Aviatik C I, and a Rumpler C I. Two heavy bombers, a VGO I and R I, had their tails and rear fuselages covered with the material.
Very soon, however, it was apparent this first attempt at a stealth airplane was a failure. A report dated July 11, 1916, states: "In clear weather, the aircraft is more difficult to spot, but in cloudy weather, it appears just as dark as other aircraft. In sunshine, the pilot and observer are unpleasantly blinded by the reflections." The major problem was the Cellon itself: "During longer periods of rain or damp weather… the covering becomes so loose that it would be better not to fly such aircraft… The covering itself is strong, but should a shrapnel go through the wing, the whole sheet would tear to pieces."
It was far more effective simply to paint the aircraft in camouflage colors. This could not make the plane invisible, as the German planes attempted to be, but would make the plane less visible.[339]
With the invention of radar in the mid-1930s, a new approach was needed. A variety of countermeasures emerged during World War II. The simplest means was strips of aluminum. Called "chaff" in the United States or "window" in England, the strips would be released from a plane. They would reflect the radar signals and produce false echoes, which would hide the plane. A more active method was to interfere with the radar. Called "noise jamming," the target plane transmitted signals on the same frequency as the radar. As the echo from a plane was a tiny fraction of the radar's original signal strength, it was possible for the plane to drown out the echo, making it impossible to detect the target plane.
With development of jet bombers like the B-47 in the late 1940s, it was thought that they would fly too high and too fast to be detected. This soon proved false, and development of electronic countermeasures (ECM) continued.[340]
During the Cold War, both the ECM and the tactics of its use grew more sophisticated. The first step was to avoid the radar entirely. The Soviet Union was vast, and many areas had little or no radar coverage. The bomber's route would take it through these gaps in the radar. The plane would not transmit any jamming signals, as this would only advertise the plane's presence. As the bomber neared the target, the number of radars would increase, and it w
ould no longer be possible to avoid them. The bomber would then start to drop chaff and jam the radars. A more subtle approach was to transmit carefully timed signals, which made the plane appear farther from the radars, or at a different bearing. This is referred to as "deception jamming." As a last resort, the air defense centers, radars, and SAM sites would be bombed.
All this was based on the idea of hiding a plane's echo. As long ago as the mid-1930s, Sir Robert Watson Watt, who designed the first British radar, realized that bombers could avoid the whole problem by having a reduced radar cross section.[341] The problem was in the details. The radar cross section of a plane depends on three factors: the shape of the plane, the frequency of the radar, and the "aspect angle" between the plane and the radar.
The prime source of a large radar cross section is two or three surfaces, such as a wing and fuselage or the floor, sides, and back of a cockpit, which meet at a right angle. The radar signal strikes one surface, is reflected to the other, then is bounced directly back to the radar. Nor were tubular shapes immune — radar signals striking a round fuselage can actually "creep" around the fuselage and back to the radar. Still other sources are sharp points on the wings or tails, wing fences, external weapons, intakes that allow the front of the engine to be "seen" by the radar, gaps formed by access panels, and antennae.
Frequency has a similar effect. A feature that has a strong radar return at one frequency may not be detectable at another. This is quite independent of size — a small vent or grill may produce a major part of the plane's radar cross section.
The final factor, aspect angle, is the most complex. The interactions between the reflections from each part of the plane cause huge changes in the radar cross section. In some cases, a one-third-degree change in the aspect angle can result in a thirty-twofold change in the radar cross section. When all these factors are taken into account, a plane's radar cross section may vary by a factor of 1 million. A 1947 text on radar design noted:
Dark Eagles: A History of the Top Secret U.S. Aircraft Page 19