"Project Bluebook" was the code name for the investigation of UFOs, or unidentified flying objects, conducted by the United States Air Force. In UFO: The Series, SHADO Commander Edward Straker, a former USAF colonel, had been one of the more active participants in that project.
As the year 1947 brought more attention to the farther reaches of outer space beyond the planet Earth, paving the way for the "International Geophysical Year" the following decade, the United States government commenced to investigate reports of so-called "flying saucers" that had begun trickling into it. It handed primary control of the investigation over to the youngest United States armed force, the Air Force.
Why the code name "Bluebook?"
At the approximate time when the Air Force was engaged in its investigations of UFOs, a publication called The Urantia Book was in print and selling a number of copies. Its cover was blue in color, and among its contents was the hypothesis that Earth had previously hosted extra-terrestrial visitors who had either begun or enriched life on Earth. Though it had previously been referred to by other code names, the references to the investigation as "Project Bluebook" stuck.
In 1969, the United States Air Force officially halted any more investigations of what, by more modern times, came to be referred to officially as "unidentified aerial events."
The final report of the Bluebook Project ultimately judged it a waste of governmental time and taxpayer money, officially declaring that the twenty-two-year-long investigation had ultimately found neither conclusive evidence of extra-terrestrial landings nor any appreciable threat to American national security.
Since the Bluebook Report had been published after the death by assassination of John Kennedy, 35th President of the United States, by which time suspicion of the American government in matters on this order was higher than it had been before, not all its conclusions were taken at face value.
Edward Straker's participation in SHADO, as its Commander, had followed his direct involvement with Project Bluebook as a United States Air Force colonel. On grounds of the possibility of culture shock, he decided to keep SHADO as secret as possible when he commanded it.