Project Blue Book was one of a series of systematic studies of unidentified flying objects (UFOs) conducted by the United States Air Force. Started in 1952, it was the second revival of such a study (the first two of its kind being Projects Sign and Grudge). A termination order was given for the study in December 1969, and all activity under its auspices ceased in January 1970.
Project Blue Book had two goals:
To determine if UFOs were a threat to national security, and to scientifically analyze UFO-related data.
Thousands of UFO reports were collected, analyzed and filed. As the result of the Condon Report (1968), which concluded there was nothing anomalous about UFOs, Project Blue Book was ordered shut down in December 1969 and the Air Force continues to provide the following summary of its investigations:
No UFO reported, investigated and evaluated by the Air Force was ever an indication of threat to our national security;
There was no evidence submitted to or discovered by the Air Force that sightings categorized as "unidentified" represented technological developments or principles beyond the range of modern scientific knowledge; and There was no evidence indicating that sightings categorized as "unidentified" were extraterrestrial vehicles.
By the time Project Blue Book ended, it had collected 12,618 UFO reports, and concluded that most of them were misidentifications of natural phenomena or conventional aircraft. According to the National Reconnaissance Office a number of the reports could be explained by flights of the formerly secret reconnaissance planes U-2 and A-12. A small percentage of UFO reports were classified as unexplained, even after stringent analysis. The UFO reports were archived and are available under the Freedom of Information Act, but names and other personal information of all witnesses have been changed.