In 1976, the Lockheed SR-71 Blackbird broke the world’s record for sustained altitude in horizontal flight at 25,929 meters (85,069 feet). The same day another SR-71 set an absolute speed record of 3,529.6 kilometers per hour (2,193.2 miles per hour), approximately Mach 3.3.
As the fastest jet aircraft in the world, the SR-71 has an impressive collection of records and history of service. The Blackbird’s owes its success to the continuum of aircraft that came before it.
Designed at Lockheed’s Skunk Works by Clarence “Kelly” Johnson, the SR-71 performed reconnaissance for the U.S. Air Force for more than 30 years and played a key role in Cold War intelligence gathering. In addition to reaching altitudes higher than 25,908 meters (85,000 feet) and cruise at speeds greater than Mach 3.2, it could survey up to 160,934 square kilometers (100,000 square miles) of territory in just one hour. Its stealthy design reduced its radar signature, and if it were fired upon by a surface-to-air missile, its evasive action was to simply accelerate and outfly the assailant.
The SR-71 originated in a post-World War II environment where reconnaissance was in high demand. American leaders needed to know about the Soviet Union’s nuclear capability, ICBM program, and military installations. President Eisenhower had approved the use of bombers and balloons in the early 1950s for intelligence gathering, but these craft were vulnerable to antiaircraft artillery and fighter-interceptors. The CIA requested designs from aerospace manufacturers for a new aircraft that would not be as susceptible to attack.
Kelly Johnson submitted his proposal for the U-2, essentially a glider with a jet engine and a panning camera in its belly. It was a slow craft and visible on radar, but it compensated for these deficiencies with its high-altitude capability. The U-2 was able to cruise at heights of more than 21,336 meters (70,000 feet), out of the reach of contemporary Soviet surface-to-air missiles and interceptors.
A joint project of the Air Force and CIA, the U-2 had great successes flying along the borders of the Soviet Union starting in 1956, eventually completing 24 successful missions. The aircraft, however, was detected on radar as soon as overflights began and it was only a matter of time before one would be intercepted. On May 1, 1960, a surface-to-air missile explosion knocked down the U-2 of Gary Powers over Soviet airspace. Soviet overflights ceased and the U-2 continued flying missions over places with less sophisticated air defense systems.
Years before the Powers incident, the CIA had commissioned a study to determine the characteristics for a reconnaissance aircraft that could not be shot down. The investigation determined that the new aircraft would need to be supersonic and have a small radar cross-section. Kelly Johnson answered the call. As the U-2 was called “Kelly’s Angel,” or “Angel,” Lockheed’s designs for its successor were designated with an “A” prefix for “Archangel.” The CIA gave the contract to Lockheed’s A-11, which was modified and secretly re-designated the A-12.
The A-12 is a single-seat, twin-engine, twin-tail design, manufactured of a titanium alloy. It carried one highly sophisticated, downward-looking film camera, but the plan was to eventually outfit the craft with an infrared camera, side-looking radar, and a gamma spectrometer. Much like the SR-71, the A-12 was about 30-meters (100-feet) long, had a wingspan of 17 meters (55 feet), and weighed 54,431 kilograms (120,000 pounds). The CIA ordered 12 of these aircraft, and starting in 1965, A-12s began flying missions as part of Operation Black Shield out of Kadena Air Force Base on Okinawa, Japan. These A-12s flew missions over Laos, North Vietnam, and North Korea.
Meanwhile, the Air Force wanted a long-range interceptor aircraft that could fly long distances at triplesonic cruise speed above 21,336 (70,000 feet) to intercept enemy bombers with Hughes Falcon air-to-air missiles. Kelly Johnson realized that the A-12 airframe might work, and designed an interceptor version of the A-12. This configuration had a second seat for the weapons officer and cut back the chines along the nose in order to fit the AN/ASG-18 Fire Control System and AIM-47A missile armament. The design was designated YF-12A in 1962 and it took its first successful Groom Lake flight in the following year. Due to budget concerns, this model never went into production. For the same reason, the A-12 airframe was never used to construct a bomber, although Curtis LeMay expressed significant interest in this possibility.
Another project stemming from the development of the A-12 was the M-21 aircraft and the D-21 drone. Two A-12s were modified to carry and launch the Lockheed D-21 remotely piloted reconnaissance drone, which would be powered by a Marquardt ramjet engine. The modified A-12s were re-designated M-21s, and were designed to take off with the D-21 and then launch the drone at speeds high enough to ignite the drone’s ramjet motor. This configuration never flew operational missions due to horrific accidents involving difficulty with drone separation that occurred during testing.
One successful offshoot of the A-12 was the SR-71 Blackbird. The U.S. Air Force had played a huge role in supporting the CIA’s A-12 program in terms of money, aerial refueling support, use of its facilities at Kadena Air Force Base, and various transport. The Air Force decided to order its own two-seat version of the A-12, a refined reconnaissance version for the Strategic Air Command. Its initial purpose would have been to conduct post-nuclear strike reconnaissance; that is, looking over the enemy’s situation after a nuclear exchange. Thankfully, this possibility seemed less and less likely, and the SR-71 was also capable of conventional intelligence gathering.
Experience gained from the A-12 program convinced the Air Force that flying the SR-71 safely required two crew members, a pilot and a Reconnaissance Systems Officer (RSO). The RSO operated the array of high-resolution cameras and electronic intelligence-gathering devices, as well as defensive systems, including a sophisticated electronic countermeasures system that could jam most tracking and targeting radar. The Blackbird’s Pratt & Whitney J58 engines were designed to operate continuously in afterburner to facilitate cruise at supersonic speeds.
Due to the excessive cost of operating both A-12 and SR-71 programs, the SR-71 was chosen to take over Operation Black Shield at Kadena in 1968. Its first operational mission was over Vietnam and subsequent missions were flown one to three times per week. Flights often lasted more than six hours and covered more than 11,265 kilometers (7,000 square miles). Imagery gathered included supply depots, harbor installations, industrial complexes, and prisoner-of-war camps.
In the following years, Blackbird crews provided important intelligence about the 1973 Yom Kippur War, the Israeli invasion of Lebanon and its aftermath, and pre- and post-strike imagery of the 1986 raid conducted by American air forces on Libya.
As space-based surveillance systems became more sophisticated and air defense systems became more effective, the Air Force chose to end the expensive program. In 1989, SR-71 operations were suspended, and the SR-71 program was soon terminated after flying for 24 years with the Strategic Air Command. Despite a brief revival of SR-71 flights in the mid-1990s, the program came to a final close in 1998.
Today, 15 of the remaining SR-71s are housed at museums across the United States, three remain property of Lockheed, and three have been kept by NASA to study aerodynamics, propulsion, structures, thermal protection materials, and instrumentation.