Lockheed SR-71 Blackbird

The Lockheed SR-71 "Blackbird" is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft that was developed and manufactured by the American aerospace company Lockheed Corporation. Its nicknames include "Blackbird" and "Habu".

The SR-71 was developed in the 1960s as a black project by Lockheed's Skunk Works division. American aerospace engineer Clarence "Kelly" Johnson was responsible for many of the SR-71's innovative concepts. Its shape was based on the Lockheed A-12, a pioneer in stealth technology with its reduced radar cross section, but the SR-71 was longer and heavier to carry more fuel and a crew of two in tandem cockpits. The SR-71 was revealed to the public in July 1964 and entered service in the United States Air Force (USAF) in January 1966.

During missions, the SR-71 operated at high speeds and altitudes (Mach 3.2 at 85,000 ft or 26,000 m), allowing it to evade or outrace threats. If a surface-to-air missile launch was detected, the standard evasive action was to accelerate and outpace the missile. Equipment for the plane's aerial reconnaissance missions included signals-intelligence sensors, side-looking airborne radar, and a camera. On average, an SR-71 could fly just once per week because of the lengthy preparations needed. A total of 32 aircraft were built; 12 were lost in accidents, none to enemy action.

From 1968, reconnaissance missions were flown from Kadena AB, Okinawa, first over North Vietnam and Laos during the Vietnam War, and later over North Korea. From 1976, missions were flown from RAF Mildenhall, UK, along the Soviet Union's Baltic and Barents Sea coastlines. Missions were also flown over Cuba, Nicaragua, Libya, and to probe nuclear weapons installations in Israel and South Africa. Unlike previous aircraft that were under the Central Intelligence Agency, SR-71 missions were flown overtly, with USAF markings, and never overflew the Warsaw Pact or China.

In 1974, the SR-71 set the record for the quickest flight between London and New York at 1 hour, 54 minutes and 56 seconds. In 1976, it became the fastest airbreathing manned aircraft, previously held by its predecessor, the closely related Lockheed YF-12. As of 2026, the Blackbird still holds both world records.

In 1989, the USAF retired the SR-71, largely for political reasons, although several were briefly reactivated before their second retirement in 1998. NASA was the final operator of the Blackbird, using it as a research platform, until it was retired again in 1999. Since its retirement, the SR-71's role has been taken up by a combination of reconnaissance satellites and unmanned aerial vehicles (UAVs). As of 2018, Lockheed Martin was developing a proposed UAV successor, the SR-72, however, as of 2026, the design remains a concept.

Development

Background

Lockheed's previous reconnaissance aircraft was the relatively slow U-2, designed for the Central Intelligence Agency (CIA). In late 1957, the CIA approached the defense contractor Lockheed to build an undetectable spy plane. The project, named Archangel, was led by Kelly Johnson, head of Lockheed's Skunk Works unit in Burbank, California. The work on project Archangel began in the second quarter of 1958, with aim of flying higher and faster than the U-2. Of 11 successive designs drafted in a span of 10 months, "A-10" was the front-runner, although its shape made it vulnerable to radar detection. After a meeting with the CIA in March 1959, the design was modified to reduce its radar cross-section by 90%. On 11 February 1960, the CIA approved a US$96 million (~$778 million in 2024) contract for Skunk Works to build a dozen A-12 spy planes. Three months later, the May 1960 downing of Francis Gary Powers's U-2 underscored the need for less vulnerable reconnaissance aircraft.

The A-12 first flew at Groom Lake (Area 51), Nevada, on 25 April 1962. Thirteen were built, plus five more of two variants: three of the YF-12 interceptor prototype and two of the M-21 drone carrier. The aircraft was to be powered by the Pratt & Whitney J58 engine, but J58 development was taking longer than scheduled, so it was initially equipped with the lower-thrust Pratt & Whitney J75 to enable flight testing to begin. The J58s were retrofitted as they became available, and became the standard engine for all subsequent aircraft in the series (A-12, YF-12, M-21), as well as the SR-71. The A-12 flew missions over Vietnam and North Korea before its retirement in 1968. The program's cancellation was announced on 28 December 1966, due both to budget concerns and because of the forthcoming SR-71, a derivative of the A-12.

Designation as SR-71

The SR-71 designation is a continuation of the pre-1962 bomber series; the last aircraft built using the series was the XB-70 Valkyrie. However, a bomber variant of the Blackbird was briefly given the B-71 designator, which was retained when the type was changed to SR-71.

During the later stages of its testing, the B-70 was proposed for a reconnaissance/strike role, with an "RS-70" designation. When the A-12's performance potential was clearly found to be much greater, the USAF ordered a variant of the A-12 in December 1962, which was originally named R-12 by Lockheed. This USAF version was longer and heavier than the original A-12 because it had a longer fuselage to hold more fuel. The R-12 also had a crew of two in tandem cockpits, and reshaped fuselage chines. Reconnaissance equipment included signals intelligence sensors, a side-looking airborne radar, and a photo camera. The CIA's A-12 was a better photo-reconnaissance platform than the USAF's R-12: since the A-12 flew higher and faster, and with only a pilot, it had room to carry a better camera and more instruments. The A-12 flew covert missions while the SR-71 flew overt missions; the latter had USAF markings and pilots carried Geneva Conventions Identification Cards.

During the 1964 campaign, Republican presidential nominee Barry Goldwater repeatedly criticized President Lyndon B. Johnson and his administration for falling behind the Soviet Union in developing new weapons. Johnson decided to counter this criticism by revealing the existence of the YF-12A USAF interceptor, which also served as cover for the still-secret A-12 and the USAF reconnaissance model since July 1964. USAF Chief of Staff General Curtis LeMay preferred the SR (Strategic Reconnaissance) designation and wanted the RS-71 to be named SR-71. Before the July speech, LeMay lobbied to modify Johnson's speech to read "SR-71" instead of "RS-71". The media transcript given to the press at the time still had the earlier RS-71 designation in places, creating the story that the president had misread the aircraft's designation. To conceal the A-12's existence, Johnson referred only to the A-11, while revealing the existence of a high-speed, high-altitude reconnaissance aircraft.

In 1968, Secretary of Defense Robert McNamara canceled the F-12 interceptor program. The specialized tooling used to manufacture both the YF-12 and the SR-71 was also ordered destroyed. Production of the SR-71 totaled 32 aircraft: 29 SR-71As, two SR-71Bs, and one SR-71C.

Design

Overview

The SR-71 was designed to fly faster than Mach 3 at altitudes above 85,000 ft (26,000 m) with the smallest radar cross-section that Lockheed could achieve, an early attempt at stealth design. Aircraft were painted black to radiate heat more effectively than bare metal, reducing the temperature of the skin and thermal stresses on the airframe. It had tandem cockpits for its crew of two: a pilot and a reconnaissance systems officer who navigated and operated the surveillance systems.

Airframe, canopy, and landing gear

Titanium was used for 85% of the structure, with much of the rest being polymer composite materials. To control costs, Lockheed used a more easily worked titanium alloy, which softened at a lower temperature. The challenges posed led Lockheed to develop new fabrication methods, which have since been used in the manufacture of other aircraft. Lockheed found that washing welded titanium requires distilled water, as the chlorine present in tap water is corrosive; cadmium-plated tools could not be used, as they also caused corrosion. Metallurgical contamination was another problem; at one point, 80% of the delivered titanium for manufacture was rejected on these grounds.

The high temperatures generated in flight required special design and operating techniques. Major sections of the skin of the inboard wings were corrugated, not smooth.

Fuselage panels were manufactured to fit only loosely with the aircraft on the ground. Proper alignment was achieved as the airframe heated up, with thermal expansion of several inches. Because of this, and the lack of a fuel-sealing system that could remain leak-free with the extreme temperature cycles during flight, the aircraft leaked JP-7 fuel on the ground before takeoff, annoying ground crews.

The outer windscreen of the cockpit was made of three layers of glass with cooling sections between them. The ANS navigation window was made of solid quartz and was fused ultrasonically to the titanium frame. The temperature of the exterior of the windscreen could reach 600 °F (320 °C) during a mission.