One common argument against the existence of any and all conspiracies is that it's impossible to keep secret any project requiring more than a few individuals.
This sounds plausible, but is it? After all, I grew up around massive secret projects. Friends of the family worked on the crown jewels of the national security state, such as Area 51, the U-2 spy plane, the awesome SR-71, and the F-117 Stealth Fighter.
Stealth work began in 1975 at both Lockheed and Northrop (which eventually became the B-2 Stealth Bomber) and Lockheed had a stealth prototype,
Have Blue, flying at Area 51 by the end of 1977. Carter's defense secretary Harold Brown announced the existence of stealth in
August 1980, claiming that leaks in the preceding days had made it impossible to keep the entire concept secret anymore. Republicans angrily claimed he spilled the beans early to defuse Reagan's attack on Carter canceling the B-1 program. The Russians apparently were still clueless about stealth. (It came as a surprise to me, too.)
Airline pilots frequently spotted the otherworldly-looking Skunk Works planes being tested out of Area 51, especially the 2000 mph 80000' altitude SR-71 which covered enormous amounts of territory and caused sonic booms (the SR-71 was announced fairly quickly by LBJ). One theory is that the U.S. government encouraged rumors of flying saucers at Area 51 to discredit these highly credible witnesses.
But all these pale in comparison to the huge Bletchley Park decoding operation in WWII England, which had a staff of nearly 10,000 working on site by the end of the war, and didn't surface in the popular press until the early 1970s. It required the history of computing to be rewritten.
Besides decoding the German Enigma machine, there were other projects at Bletchley that weren't declassified until much more recently, such as
Tunny, the breaking of Hitler's personal cipher.
An obituary in today's NYT:
Jerry Roberts, Last of Team of British Code Breakers, Dies at 93
By PAUL VITELLO APRIL 2, 2014
Jerry Roberts, the last surviving member of the British code-breaking team that cracked strategic ciphers between Hitler and his top generals, helping to hasten the end of World War II, died on March 25 in Hampshire, England. He was 93.
His death was confirmed by the Bletchley Park Trust, a nonprofit group that administers the Victorian estate north of London where the British government lodged Mr. Roberts and hundreds of other code breakers during the war, among them linguists, mathematicians and puzzle masters of various backgrounds.
Mr. Roberts, a German linguist, was part of a small top-secret group assembled in 1941 to help decrypt messages picked up in radio signals between Hitler and his field marshals on the front. The team’s very existence remained a secret until 2006, when the British government declassified wartime intelligence files.
This 2006 date seems exaggerated. Here's the obituary in
The Telegraph from 2002 of Roberts' colleague W.T. Tutte:
PROFESSOR BILL TUTTE, who has died aged 84, was responsible for one of Bletchley Park's greatest codebreaking achievments during the Second World War when he cracked the teleprinter cipher, known as Tunny, which Hitler used to communicate with his generals. ...
This was a far more complicated mechanism than the famous Enigma cipher machine, since the Lorenz SZ40 had 12 wheels compared with the three or four on the Enigma.
It also led to Bletchley Park's other great achievement, the construction of the world's first semi-programmable electronic computer, Colossus, which was used to decipher the Tunny messages.
Looking at the
bibliography on Wikipedia, there are sources for the Tunny decryption going back to 1993, but that's still a half century after
William Tutte broke Tunny in a tour de force of cryptography.
Roberts' NYT obituary continues:
By 1941, Bletchley Park cryptographers had already deciphered thousands of messages transmitted by lower-level German commanders in the field, thanks to the work of the mathematician Alan Turing, who in 1940 cracked the daunting German secret code that the British called Enigma. But they were stumped by the even more complex ciphered messages being transmitted among Hitler and the generals Erwin Rommel, Wilhelm Keitel, Gerd von Rundstedt and Alfred Jodl.