From 1948 until 1969, the U.S. government collected about 80,000 pages of first-hand reports—including descriptions, drawings, and diagrams—on more than 12,000 sightings of UFOs. Begun as Project Sign, it was quickly renamed Project Grudge, then Project Blue Book in early 1952. The new moniker, inspired by the blue books college students use to take written exams, was supposed to indicate the seriousness with which the study was being undertaken.
With 1,500 reports, 1952 was also the year with the most sightings. All in all, 701 remain "unidentified" to this day. The rest were attributed to a variety of sources, including bright planets, auroras, aircraft, searchlights, and birds. Project Blue Book was shut down in 1969 after a rigorous study led by the physicist Edward Condon concluded that UFO sightings all had mundane, nonthreatening explanations. Since that time, the U.S. government no longer investigates claims of "flying saucers"—a term that dates back to the first widely reported UFO sighting by an American businessman in 1947. Independent groups of civilians still maintain that the government intentionally withholds information about UFO sightings, both past and present.
There's plenty of controversy and intrigue
involved with the Condon Report.