[[Fil:Appendix I to Project Blue Book Status Report Number 8 - NARA - 595542.jpg|thumb|''Appendix I to Project Blue Book Status Report Number 8'': Denne graf viser UFO-rapportfrekvensen for månederne juni, juli, august og september 1952.]]
I mere end 20 år, fra 1948 til 1969 ledede det amerikanske luftvåben efterforskningen af [[ufo]]-rapporter. Igennem det meste af perioden lå ansvaret hos en special-arbejdsgruppe med kodenavnet '''''Project Blue Book'''''.<ref>[https://vault.fbi.gov/Project%20Blue%20Book%20%28UFO%29%20 vault.fbi.gov: Project Blue Book (UFO)], [https://web.archive.org/web/20110413172933/http://vault.fbi.gov/Project%20Blue%20Book%20%28UFO%29%20/ backup]</ref><ref>[https://web.archive.org/web/20110414071312/http://vault.fbi.gov/Project%20Blue%20Book%20%28UFO%29%20/Project%20Blue%20Book%20%28UFO%29%20part%201%20of%201/at_download/file vault.fbi.gov: bluebook.pdf (Blue Book omtale)]</ref><ref>[https://archive.today/20120719123429/http://www.af.mil/information/factsheets/factsheet_print.asp?fsID=188&page=1 af.mil: U.S. Air Force Fact Sheet: UNIDENTIFIED FLYING OBJECTS AND AIR FORCE PROJECT BLUE BOOK] Citat: "...As a result of these investigations, studies and experience gained from investigating UFO reports since 1948, the conclusions of Project Blue Book were: No UFO reported, investigated and evaluated by the Air Force was ever an indication of threat to our national security;..."</ref><ref name="quintanilla">[https://web.archive.org/web/20051016063903/http://www.nidsci.org/pdf/quintanilla.pdf UFO’S: AN AIR FORCE DILEMMA. Lt. Col Hector Quintanilla. USAF (ret.). Former Chief, Project Blue Book. 1974] Citat: "...The behind-the-scenes story of an official Government project that cost the taxpayers $20,000,000, which tells why the project did not justify its cost...Contrary to popular belief, unidentified objects are not a new phenomenon. Historians have been recording the sightings of unidentified objects since before the coming of Christ...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. It is unlikely that positive proof of their existence will be obtained without examination of the remains of crashed objects. Proof of non-existence is equally impossible to obtain unless a reasonable and convincing explanation is determined for each incident...“Blue Book” came into its own in March, 1952, and the nick name stayed with the project until it was terminated on 29 December 1969 (or 70?)...The fact UNIDENTIFIED FLYING OBJECTS are to be reported surprises some people, but it shouldn’t really. Our Air Defense forces are constantly alert and they are ready to take immediate action...And finally we arrive at the mysterious UNIDENTIFIED category...Another organization with a wide following, and international in scope, was the [[Aerial Phenomena Research Organization]] (APRO), which has its headquarters in Alamogordo, New Mexico...Projects Blue Book, Grudge, and Sign have been retired and so ends another chapter of Air Force contribution to American history...The Air Force has kept detailed records of all UFO reports which have been submitted to the Project office at Wright-Patterson Air Force Base...I realize that the proponents of extraterrestrial visitation will cry out in dismay over my uneducated statement, but the truth of the matter is that we Americans have a history of being romantics and often imagine the impossible dreams. If you believe in extraterrestrial visitation, then for everyone’s sake, present your evidence, state your facts, and let the true scientists of our nation be the judges. Let’s quit exploiting the masses; because if you are the founder of an extraterrestrial vehicle, it will be self-evident and fame and fortune await you beyond your wildest dreams..."</ref> ''Project Blue Book'' efterfulgte to af luftvåbnets tidligere undersøgelser - projekterne Sign<ref name="quintanilla"/> og Grudge<ref name="quintanilla"/> - som havde kludret i det på grund af manglende erfaring og ustrukturerede arbejdsmetoder.
Filosofi Historie