Project Blue Book: the Air Force’s UFO files
Twenty-two years, 12,618 reports, and one famous number: 701.
How this site works. Every fact is in our own words with its source linked beside it. The pictures are our own drawings. We never say aliens have been found, because nobody has shown that they have; we show what was reported, then what the evidence says.
From 1947 to 1969, 12,618 sightings were reported to Project Blue Book (counting the earlier projects too). US National Archives
Of those, 701 stayed “unidentified”. US National Archives
Before Blue Book
As reports grew, the US Air Force began an investigation called Project Sign in 1948. Britannica
Its investigators first thought UFOs were most likely advanced Soviet aircraft, though some suggested spacecraft from other worlds. Britannica
Sign became Project Grudge, which in 1952 was replaced by Project Blue Book, the longest-running official UFO inquiry. Britannica
How it worked
Project Blue Book began in March 1952 and took reports from the public as well as the military. Britannica, Blue Book
It was based at Wright-Patterson Air Force Base, near Dayton, Ohio. Britannica, Blue Book
It was named after the blue exam booklets used in American colleges, to suggest a careful, methodical approach. Britannica, Blue Book
Its staff created a standard questionnaire for sighting reports. Britannica, Blue Book
What the reports turned out to be
Most sightings got ordinary explanations; the biggest single group was mistaken military or civilian aircraft. Britannica, Blue Book
A CIA history declassified in 2014 says U-2 and later OXCART spy-plane flights accounted for more than half of all UFO reports in the late 1950s and most of the 1960s. Britannica
The unidentified cases included ones where there wasn’t enough information to match a known cause. Britannica
1952: the busy year
1952 had 303 unexplained sightings, many of them over Washington, D.C., that July. Most years had about a dozen. Britannica, Blue Book
The 1952 Washington sightings, on radar and by eye, were put down to temperature inversions in the air over the city, though not everyone was convinced. Britannica
The scientists
In 1953 a panel of scientists led by physicist H.P. Robertson met for three days and reviewed films and photographs of UFOs. Britannica
The panel concluded that 90 per cent of sightings could easily be put down to things like bright planets and stars, meteors, aircraft, balloons, birds and searchlights, and that there was no evidence for alien visitors. Britannica
Parts of the panel’s report stayed secret until 1979, which helped fuel suspicions of a cover-up. Britannica
A University of Colorado study led by physicist Edward Condon looked in detail at 59 sightings and found no evidence of anything but ordinary phenomena. Britannica
The end
Project Blue Book was closed on 17 December 1969. Britannica, Blue Book
Its conclusions: no UFO was ever a threat to US security, and there was no evidence that the “unidentified” sightings were beyond known science or were vehicles from space. US National Archives
No physical evidence of anything from another world was collected during the project. Britannica, Blue Book
Debunking, or careful science?
Astronomer J. Allen Hynek, the project’s lead scientist throughout, was privately critical of its lack of rigour and its emphasis on debunking. Britannica, Blue Book
Hynek later concluded that a small fraction of the most reliable reports pointed to visitors from space, and founded the Center for UFO Studies. Britannica
Hynek was the project’s own scientist, so his doubts are part of the record too.
Which years?
From 1947 to 1969, 12,618 sightings were reported to Project Blue Book (counting the earlier projects too). US National Archives
Britannica’s UFO article gives the same 12,618 total but dates it from 1952 to 1969. Britannica
Read the files yourself
Blue Book’s declassified records have been at the US National Archives in Washington, D.C., since 1976, open to the public. Britannica, Blue Book
Today you read them on 94 rolls of microfilm in the National Archives’ reading room. US National Archives
Our view: 701 unexplained reports out of 12,618 sounds spooky until you remember that “unexplained” often meant “not enough information”. Our favourite fact: secret spy planes caused more UFO reports than anything from space ever has.
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