Finally, decades after the United States Air Force closed their official investigations into the UFO phenomenon, the files are online in their entirety for free.
Project Blue Book is regarded as the third UFO investigation project by the USAF. The first was Project Sign, which began in 1947, then Grudge, which ran from 1949 to 1951, and the final project, Blue Book, ran from 1951 to 1969. The files surrounding the investigation of the sightings are all included in the Project Blue Book files. That is, unless, as some suggest, there are secret investigations that the public still does not have access to.