Project Blue Book
From 1947 to 1969, the United States Air Force ran three successive investigations into UFOs — Project Sign, Project Grudge, and finally Project Blue Book, the longest and best known of them. Across all three, the government examined 12,618 reports. It closed 701 of them as unidentified. What the programs actually did — and didn't do — sits underneath almost every case discussed elsewhere on this site.
The baseline everything since has been measured against.
Project Blue Book was established in March 1952 at Wright-Patterson Air Force Base in Dayton, Ohio, as the third and longest-running of the Air Force's official UFO investigations. It followed two smaller predecessors, Project Sign and Project Grudge, which together had already logged several hundred sightings in the years right after Kenneth Arnold's 1947 sighting and the Roswell incident that same summer.
Its first director, Captain Edward J. Ruppelt, coined the term "UFO" specifically to replace "flying saucer," which he considered too loaded to support a methodical investigation. The project's later scientific consultant, astronomer J. Allen Hynek, would go on to found the Center for UFO Studies and popularize the "Close Encounters" classification system still used informally today.
The program's mandate was narrow and specific: determine whether UFO reports represented a threat to national security, and separately, whether any represented technology beyond what was publicly known. It was not designed, and never claimed, to settle the broader question of extraterrestrial life.
The two numbers the record actually supports
Category-by-category breakdowns of the 12,618 cases circulate widely, but this site could not confirm any single version of that split against the Air Force's own official record closely enough to publish it. These two figures are the ones consistently documented across Air Force and National Archives sources.
From Kenneth Arnold to closure
Project Sign, then Project Grudge
Following the 1947 "flying saucer" sightings and Roswell, the Air Force's first classified investigation, Project Sign, logged 243 reports before being scaled down into Project Grudge, which added roughly 244 more.
Project Blue Book is established
Operating under the Air Technical Intelligence Center, with a dual mandate: assess national security risk, and analyze the reports scientifically rather than dismiss them outright.
Thousands of cases, one at a time
Witness interviews, radar data, photographs, and physical evidence were gathered and compared case by case — the same categories of evidence discussed on What Recorded It?. Classified programs like the U-2 and A-12 OXCART later explained a portion of Cold War-era sightings the investigators could not identify publicly at the time.
The Condon Report
A University of Colorado study, commissioned by the Air Force, concluded that further systematic study of UFOs was unlikely to be productive — a conclusion that became the primary justification for ending the program.
The project closes
The Air Force concluded that no unidentified case had demonstrated a threat to national security or evidence of technology beyond known science. 701 cases remained formally unresolved.
The files become public
After redaction was completed, the records became available for public research at the National Archives — the closest thing this era of the record has to an open ledger.
Project Blue Book closed the question of national security. The 701 cases remained unresolved — and the questions they represent still echo through the modern Congressional record.