Key point: More than a half-century later, the SR-71 is a museum piece. But secret aircraft projects, and strange sightings over the western United States, have not stopped.

There are few secret projects like U.S. Air Force black projects, and that was certainly the case for the famed SR-71 Blackbird.

The SR-71 was no ordinary aircraft but a big, beautiful and state-of-the-art spy plane designed in the 1950s and early 1960s to fly quickly at high altitudes over the Soviet Union, filling in for the U-2 Dragon Lady which had become vulnerable to then-new surface-to-air missiles.

Designer Lockheed and the Air Force treated the project with intense secrecy, and when still totally classified, the CIA recorded any hints that reporters, analysts or civilian plane watchers might have as to the jet’s existence. It didn’t matter who suspected it. If airport cab drivers were spreading rumors about secret doings at Lockheed, the agency wanted to know.

To keep the program under wraps, Lockheed engineers quietly worked on the plane at the company’s Skunk Works division in Burbank, California and the Air Force’s isolated Nevada base — known as Area 51 — beginning in 1958. The first Blackbird flew four years later.

The government surrounded the Blackbird with so much silence because it was an experimental plane and the first stealth aircraft, owing to its radar-reflective design. The SR-71's extreme performance — a speed of Mach 3.3 at an altitude of 85,000 feet — was highly sensitive information.

However, aviation experts and the press picked up on the project and did so relatively quickly, sometimes through sheer guesswork, according to the CIA’s recently declassified official history obtained by Governmentattic.org.

The first outsider to notice was John B. Pearson, a retired admiral who was then working for North American Aviation, the company which built the legendary F-86 Sabre and X-15 rocket plane. As it was his job to study the military aircraft industry, he suspected by April 1962 that the Air Force, Lockheed and the CIA were up to something big.

He had several reasons for the hunch. For one, Lockheed’s chief SR-71 designer, Clarence “Kelly” Johnson, had become hard to reach. Pearson also speculated to a friend working at Hughes Aircraft Company that engineers developing the firm’s GAR-9 missile must be assisting a secret aircraft program at Lockheed, because the F-108 Rapier — the only known plane which could fire the missile — had been cancelled.

In fact, Lockheed was developing an (eventually cancelled) interceptor version of the Blackbird which would have carried the GAR-9. “The old friend was noticeably startled and changed the subject which Pearson took as another clue,” the CIA recorded in a document listing examples of industry suspicions of the Blackbird project.

In any case, Pearson knew his stuff — and he knew that a long-range, high-speed and high-altitude surveillance plane was exactly what the Pentagon needed given the growing vulnerabilities of the U-2.

In January 1963, a manager named William Clegern at a Denver technology firm speculated that “Lockheed was working on a super U-2,” according to the CIA history. Like Pearson, Clegern had made an educated guess, although he had some help from an “unrecalled source” during a visit to Los Angeles.

In a tightly-knit industry with overlapping suppliers of hardware and spare parts, word got around — and traveling vendors were often a source of grist for the rumor mill.

Robert Widmer, then vice president of Convair, reported that it was “generally known” in the industry, particularly on the West Coast, that Lockheed was working on a similar but more advanced successor to the U-2.

Pearson and his colleagues at North American Aviation were also aware that the Pentagon was pouring millions of dollars into developing the huge J-58 turbojet engine — of which the SR-71 fitted two.

“They observed that the funds allotted to developing the J-58 did not seem to them justified unless there was some high altitude airplane available in which to utilize the J-58,” the CIA noted.

By March, Pearson and his coworkers studied shipments of liquid hydrogen and oxygen fuel, movements of test pilots and even subcontractors working on specialized precision valves to deduce not only the existence of a new spy plane, but guess its specifications. They weren’t dead-on accurate, but they were close.

Taxi drivers shuttling Lockheed contractors from Los Angeles’ airport to the company’s terminal started asking questions. Even airline crews had spotted the A-12 Oxcart — a shorter version of the SR-71 flown by the CIA — in flight.

And the media got involved.

In January 1963, Fort Worth aviation newspaper Cross Country News reported that sources spoke of a “highly guarded … super-sonic transport” in the works at Lockheed, apparently mixing up the Blackbird with the U.S. supersonic transport program.

“Even in the X stage Lockheed officials say nothing,” the paper reported. “No details came from this tip, from sources considered highly reliable.”

Then disaster struck. On May 24, an A-12 stalled, went into an unrecoverable spin and crashed during a test flight in Utah. Fortunately, pilot Kenneth Collins ejected and survived.

Even in remote Utah, it’s hard to hide a crash. A local deputy witnessed the incident and a vacationing family snapped away with a camera. The CIA promptly seized their photographs and paid $25,000 each to the deputy and the family to keep quiet, according to a 2010 story in the Seattle Times.

The Associated Press reported on the incident and described the crashed aircraft as a “jet trainer.” The same day, the Las Vegas Review-Journal published a story stating the plane was an F-105 Thunderchief fighter-bomber, citing Air Force officials.

The “Thunderchief” claim was an elaborate cover story. But by July, Robert Hotz — longtime editor of Aviation Week and a former bomber pilot during World War II — “indicated his awareness of developments at Burbank.”

And in November, a Los Angeles Times reporter began making phone calls to engine maker Westinghouse, asking questions about CIA involvement in a secret project in “the desert.” The Fontana Herald News ran an article in November “speculating about a ‘super secret project site.’”

The Blackbird wouldn’t stay officially secret for much longer. Pres. Lyndon Johnson would run for election in 1964, and to counter criticisms from Republican Sen. Barry Goldwater, revealed the SR-71 during a speech on July 25.

More than a half-century later, the SR-71 is a museum piece. But secret aircraft projects, and strange sightings over the western United States, have not stopped. When observers notice and publicize their suspicions, an anonymous official is somewhere, surely, typing away notes.

This article first appeared in 2016.