DANBURY, Conn.      (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.
 He is sitting  in the food court at the Danbury Fair mall, where a group of retired  co-workers from the former Perkin-Elmer Corp. gather for a weekly  coffee. Gray-haired now and hard of hearing, they have been meeting here  for 18 years. They while away a few hours nattering about golf and  politics, ailments and grandchildren. But until recently, they were  forbidden to speak about the greatest achievement of their professional  lives.
 "Ah, Hexagon," Ed Newton says, gleefully exhaling the word that stills feels almost treasonous to utter in public.
 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 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.
 Though other  companies were part of the project - Eastman Kodak made the film and  Lockheed Corp. built the satellite - the cameras and optics systems were  all made at Perkin-Elmer, then the biggest employer in Danbury.
 "There were many days we arrived in the dark and left in the dark," says retired engineer Paul Brickmeier, 70.
 He  recalls the very first briefing on Hexagon after Perkin-Elmer was  awarded the top secret contract in 1966. Looking around the room at his  30 or so colleagues, Brickmeier thought, "How on Earth is this going to  be possible?"
 One thing that made it possible  was a hiring frenzy that attracted the attention of top engineers from  around the Northeast. Perkin-Elmer also commissioned a new  270,000-square-foot building for Hexagon - the boxy one on the hill.
 Waiting  for clearance was a surreal experience as family members, neighbors and  former employers were grilled by the FBI, and potential hires were  questioned about everything from their gambling habits to their  sexuality.
 "They wanted to make sure we couldn't be bribed," Marra says.
 Clearance  could take up to a year. During that time, employees worked on  relatively minor tasks in a building dubbed "the mushroom tank" - so  named because everyone was in the dark about what they had actually been  hired for.
 Joseph Prusak, 76, spent six  months in the tank. When he was finally briefed on Hexagon, Prusak, who  had worked as an engineer on earlier civil space projects, wondered if  he had made the biggest mistake of his life.
 "I  thought they were crazy," he says. "They envisaged a satellite that was  60-foot long and 30,000 pounds and supplying film at speeds of 200  inches per second. The precision and complexity blew my mind."
 Several  years later, after numerous successful launches, he was shown what  Hexagon was capable of - an image of his own house in suburban  Fairfield.
 "This was light years before Google Earth," Prusak said. "And we could clearly see the pool in my backyard."
 There  had been earlier space spy satellites - Corona and Gambit. But neither  had the resolution or sophistication of Hexagon, which took close-range  pictures of Soviet missiles, submarine pens and air bases, even entire  battalions on war exercises.
 According to the  National Reconnaissance Office, a single Hexagon frame covered a ground  distance of 370 nautical miles, about the distance from Washington to  Cincinnati. Early Hexagons averaged 124 days in space, but as the  satellites became more sophisticated, later missions lasted twice as  long.
 "At the height of the Cold War, our  ability to receive this kind of technical intelligence was incredible,"  says space historian Dwayne Day. "We needed to know what they were doing  and where they were doing it, and in particular if they were preparing  to invade Western Europe. Hexagon created a tremendous amount of  stability because it meant American decision makers were not operating  in the dark."
 Among other successes, Hexagon  is credited with providing crucial information for the Strategic Arms  Limitation Talks between the United States and the Soviet Union in the  1970s.
 From the outset, secrecy was a huge  concern, especially in Danbury, where the intense activity of a  relatively small company that had just been awarded a massive contract  (the amount was not declassified) made it obvious that something big was  going on. Inside the plant, it was impossible to disguise the gigantic  vacuum thermal chamber where cameras were tested in extreme conditions  that simulated space. There was also a "shake, rattle and roll room" to  simulate conditions during launch.
 "The  question became, how do you hide an elephant?" a National Reconnaissance  Office report stated at the time. It decided on a simple response:  "What elephant?" Employees were told to ignore any questions from the  media, and never confirm the slightest detail about what they worked on.
 But  it was impossible to conceal the launches at Vandenberg Air Force base  in California, and aviation magazines made several references to "Big  Bird." In 1975, a "60 Minutes" television piece on space reconnaissance  described an "Alice in Wonderland" world, where American and Soviet  intelligence officials knew of each other's "eyes in the sky" - and  other nations did, too - but no one confirmed the programs or spoke  about them publicly.
 For employees at Perkin-Elmer, the vow of secrecy was considered a mark of honor.
 "We  were like the guys who worked on the first atom bomb," said Oscar  Berendsohn, 87, who helped design the optics system. "It was more than a  sworn oath. We had been entrusted with the security of the country.  What greater trust is there?"
 Even wives - who  couldn't contact their husbands or know of their whereabouts when they  were traveling - for the most part accepted the secrecy. They knew the  jobs were highly classified. They knew not to ask questions.
 "We  were born into the World War II generation," says Linda Bronico, whose  husband, Al, told her only that he was building test consoles and  cables. "We all knew the slogan `loose lips sink ships.'"
 And  Perkin-Elmer was considered a prized place to work, with good salaries  and benefits, golf and softball leagues, lavish summer picnics (the  company would hire an entire amusement park for employees and their  families) and dazzling children's Christmas parties.
 "We loved it," Marra says. "It was our life."
 For  Marra and his former co-workers, sharing that life and their long-held  secret has unleashed a jumble of emotions, from pride to nostalgia to  relief - and in some cases, grief.
 The city's  mayor, Mark Boughton, only discovered that his father had worked on  Hexagon when he was invited to speak at an October reunion ceremony on  the grounds of the former plant. His father, Donald Boughton, also a  former mayor, was too ill to attend and died a few days later.
 Boughton  said for years he and his siblings would pester his father - a  draftsman - about what he did. Eventually they realized that the topic  was off limits.
 "Learning about Hexagon makes  me view him completely differently," Boughton says. "He was more than  just my Dad with the hair-trigger temper and passionate opinions about  everything. He was a Cold War warrior doing something incredibly  important for our nation."
 For Betty Osterweis  the ceremony was bittersweet, too. Not only did she learn about the  mystery of her late husband's professional life. She also learned about  his final moments.
 "All these years," she  said, "I had wondered what exactly had happened" on that terrible day in  1987 when she received a phone call saying her 53-year-old husband,  Henry Osterweis, a contract negotiator, had suffered a heart attack on  the job. At the reunion she met former co-workers who could offer some  comfort that the end had been quick.
 Standing  in the grounds of her late husband's workplace, listening to the  tributes, her son and daughter and grandchildren by her side, Osterweis  was overwhelmed by the enormity of it all - the sacrifice, the secrecy,  the pride.
 "To know that this was more than  just a company selling widgets ... that he was negotiating contracts for  our country's freedom and security," she said.
 "What a secret. And what a legacy."