Sign, Grudge, and Blue Book: The U.S. Air Force's Three-Program UFO Investigation and Its Archival Legacy

To the point

The piece traces how the U.S. Air Force studied UFO sightings through three programs—Sign, Grudge, and Blue Book—began after Kenneth Arnold’s 1947 sighting, concluded Sign was inconclusive, Grudge found many reports were misinterpretations or hoaxes, and Blue Book (1952–1969) said none posed a national security threat, no sightings showed advanced tech, and none were proven extraterrestrial, then moved the records to the National Archives in 1975 where redacted files were made available for public research, with displays and selected materials (including Arnold’s 1947 document and charts) illustrating the ongoing public interest and Blue Book’s lasting influence on how such reports are documented and studied, as explained by archivist Joseph Gillette.