Project SIGN (1948–1949) vs. Project Blue Book (1952–1969)
Two successive U.S. Air Force investigations of unidentified aerial objects, separated by a three-year gap, each reached public conclusions about their findings. This comparison draws each program's scope, era, and stated conclusion from the historical record held in the National Archives.
Project SIGN (January 1948 – February 1949)
Project SIGN was the first organized U.S. Air Force study of UFO reports, activated by the Air Technical Intelligence Center (ATIC) on 23 January 1948. In its February 1949 technical report, Project SIGN concluded that "no definite and conclusive evidence is yet available that would prove or disprove the existence of these unidentified objects as real aircraft of unknown and unconventional configuration," and attributed most sightings to misinterpretation of known objects, hysteria, hallucination, or hoax. It did not rule out other possibilities and recommended continued military intelligence handling of UFO investigations.
Project Blue Book (March 1952 – December 1969)
Project Blue Book was the longest-running U.S. Air Force investigation of UFO phenomena, based at Wright-Patterson Air Force Base. It recorded 12,618 UFO sightings between 1947 and 1969. The Air Force states that no sighting it investigated indicated a threat to national security, showed evidence of technology beyond then-present scientific knowledge, or represented an extraterrestrial vehicle; 701 of the 12,618 sightings remained categorized as unidentified. The Secretary of the Air Force announced the program's termination in December 1969.
Source: https://www.archives.gov/research/military/air-force/ufos
UAP Records Archive is an independent public archive and is not an official or government source. Statements above faithfully restate the cited official records; the original documents are authoritative.