ASHIYA AB JAPAN, October 1952October 1952

On the nights of October 15 and 16, 1952, radar operators at Ashiya Air Base in Japan detected multiple unidentified objects on their radar scopes. The objects appeared as blips similar to light aircraft and moved across the radar screens at speeds between 50 and 70 miles per hour. As many as five targets were tracked at the same time. They appeared at altitudes between 200 and 500 feet and traveled generally from north to south, approaching from within two miles of the airfield before disappearing into ground clutter (the radar interference caused by the terrain around the base) near the runway. The sighting lasted several hours across both nights. Nothing was seen with the naked eye, and no unusual sounds were heard.

The radar operators who filed reports had between 10 months and 5 years of experience with the AN/MPN-1 radar sets used to track the objects. All four operators submitted witness statements. Three of them believed the objects were birds. One operator stated he did not know what the objects were and did not wish to guess. The supervising officer noted that pilots flying in the area reported seeing nothing.

Air Force investigators found no physical evidence such as photographs or fragments. They noted that weather conditions at the time were reasonably clear, with visibility of 10 miles and a cloud ceiling of 4,000 feet. Because no visual confirmation was made, no sounds were heard, and the opinions of three witnesses pointed to birds, the investigating officer concluded it was probable the objects were large birds. The Air Force officially evaluated the case as "probably balloon" based on the case card, though the detailed analysis suggested birds as the most likely explanation.

The full case file is reproduced below as held by the National Archives, consisting of 7 pages.