Project Blue Book and predecessors investigated 12,618 UFO reports; 701 remained unidentified. The roots of Project Sign began on June 24, 1947 when pilot Kenneth Arnold reported seeing nine flat disc-like aircraft flying at a high rate of speed near Mt. Rainer, Washington. Many similar reports followed.

Some UFOlogists theorize that researchers labeled mysterious sightings as misidentified phenomena because members of the organization were pressured to identify UFO sightings to ease public apprehension. This been supported by the CIA's release of documents with information about the project. Some believe that Project Blue Book is associated with the cover-up of investigations into aliens visitations to Earth.

Dr. Kevin Randle’s Study of Project Blue Book

After investigating the operation’s files, journalist Dr. Kevin Randel found 4,000 unexplained cases. A retired Air Force Captain, he has been studying the UFO phenomenon for more than twenty-five years. Randle admits that many sightings are hoaxes or otherwise explainable as natural phenomena, such as stars, ball lightning and atmospheric conditions.