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CloseThe release includes incidents dating back to 1952, including footage filmed near Tremonton, Utah, by US Navy Chief Warrant Officer Delbert C. Newhouse, who reported seeing and filming a group of bright airborne objects.
Submitted to the US Air Force shortly afterwards, the footage later became one of the visual cases reviewed by Project Blue Book, the Air Force's UFO investigation programme, which ran from 1952 to 1969.
However, the film's limited detail and lack of fixed reference points meant investigators could not reach a definitive conclusion.
After US President Donald Trump called for UFO files to be released in an executive order earlier this year, the Pentagon has declassified hundreds of files in a series of six drops.
The first tranche of 161 files was uploaded to the US defence department's website on 8 May, with promises of more to come.
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