DANBURY, Connecticut (AP) — For more than a decade they toiled in the strange, boxy-looking building on the hill above the municipal airport, the building with no windows (except in the cafeteria), the building filled with secrets.

They wore protective white jumpsuits, and had to walk through air-shower chambers before entering the sanitized "cleanroom" where the equipment was stored.

They spoke in code.

Few knew the true identity of "the customer" they met in a smoke-filled, wood-paneled conference room where the phone lines were scrambled. When they traveled, they sometimes used false names.

At one point in the 1970s there were more than 1,000 people in the Danbury area working on The Secret. And though they worked long hours under intense deadlines, sometimes missing family holidays and anniversaries, they could tell no one — not even their wives and children — what they did.

They were engineers, scientists, draftsmen and inventors — "real cloak-and-dagger guys," says Fred Marra, 78, with a hearty laugh ...

It was dubbed "Big Bird" and it was considered the most successful space spy satellite program of the Cold War era. From 1971 to 1986 a total of 20 satellites were launched, each containing 60 miles (100 kilometers) of film and sophisticated cameras that orbited the earth snapping vast, panoramic photographs of the Soviet Union, China and other potential foes. The film was shot back through the earth's atmosphere in buckets that parachuted over the Pacific Ocean, where C-130 Air Force planes snagged them with grappling hooks.

The scale, ambition and sheer ingenuity of Hexagon KH-9 was breathtaking. The fact that 19 out of 20 launches were successful (the final mission blew up because the booster rockets failed) is astonishing.

So too is the human tale of the 45-year-old secret that many took to their graves.

Hexagon was declassified in September. Finally Marra, Newton and others can tell the world what they worked on all those years at "the office."

"My name is Al Gayhart and I built spy satellites for a living," announced the 64-year-old retired engineer to the stunned bartender in his local tavern as soon as he learned of the declassification. He proudly repeats the line any chance he gets.

"It was intensely demanding, thrilling and the greatest experience of my life," says Gayhart, who was hired straight from college and was one of the youngest members of the Hexagon "brotherhood".

He describes the white-hot excitement as teams pored over hand-drawings and worked on endless technical problems, using "slide-rules and advanced degrees" (there were no computers), knowing they were part of such a complicated space project. The intensity would increase as launch deadlines loomed and on the days when "the customer" — the CIA and later the Air Force — came for briefings. On at least one occasion, former President George H.W. Bush, who was then CIA director, flew into Danbury for a tour of the plant ...