Project Blue Book was one of a series of systematic studies of Unidentified flying objects (UFOs) conducted by the United States Air Force (U.S.A.F.). Started in 1952, it was the second revival of such a study. 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, which concluded there was nothing anomalous about any UFOs, Project Blue Book was ordered shut down in December 1969. This project was the last publicly known UFO research project led by the USAF.
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 (clouds, stars, et cetera) or conventional aircraft. A few were considered hoaxes. 701 of the reports about six percent were classified as unknowns, defying detailed 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 redacted.
Though many accepted Blue Book's final conclusions that there was nothing extraordinary about UFOs, critics then and now have charged that Blue Book, especially in its later years, was engaging in dubious research, or even perpetuating a cover up of UFO evidence. Some evidence suggests that not only did some UFO reports bypass Blue Book entirely, but that the U.S. Air Force continued collecting and studying UFO reports after Blue Book had been discontinued, despite official claims to the contrary.