JAPAN, April 1952April 1952

On April 18 or 19, 1952, a radar operator at a U.S. Air Force detachment in Japan detected an unidentified object on his radar scope. The operator worked at Detachment 721 of the 618th Aircraft Control and Warning Squadron, part of the Japan Air Defense Force. The object appeared on the radar screen at 1207 hours (12:07 p.m.) and disappeared at 1209 hours (12:09 p.m.). The entire sighting lasted only about two minutes.

The radar operator used a TPS-1B radar set to track the object. According to the radar data, the object measured approximately five to six degrees in length and two to three miles in width on the Plan 12 indicator display. The radar calculated the object's speed at roughly 2,700 miles per hour. The object's brightness on the radar screen appeared normal. The operator tracked the object as it moved across several specific geographic coordinates, changing course multiple times. It first headed due north, then shifted to a northwest heading of about 310 degrees, and finally assumed a heading of roughly 220 degrees before fading from the scope.

The radar operator who made the observation was considered reliable and had six months of experience in his position. Weather conditions at the time were fair with calm seas and visibility of approximately five miles with haze. The Air Force noted that the area where the object appeared was not a heavy traffic zone, though some aircraft had been plotted there previously. However, none of the aircraft previously sighted in that area had traveled at a speed comparable to the 2,700 miles per hour recorded for this object.

In a technical assessment, an electronics officer noted that because the target appeared for only two minutes, an acceptable explanation was impossible. The radar set appeared to be operating normally before and after the incident, and the size, shape, and location of the signal made equipment malfunction seem unlikely. The complete case file, consisting of eight pages, is reproduced below as held by the National Archives.