(SE Of Japan) 34DEG15'N-139DEG30'E, May 1952May 1952

On May 30, 1952, the pilot, co-pilot, and engineer of a C-54 transport plane spotted an unidentified object southeast of Japan near Oshima at around 1900 to 1930 hours (7:00 to 7:30 p.m.). The crew was flying at 8,500 feet on a heading of 190 degrees. All three crew members agreed the object appeared round and dark, and that it hovered in place.

The co-pilot, Captain William Leet, and the engineer, T/Sgt. Andrew Roe, watched the object for five to seven minutes. They said it had no visible exhaust flames and showed no means of propulsion. Both men were convinced it was neither a cloud nor a balloon, and that it was unlike any aircraft they had ever seen. The engineer reported seeing what looked like a short tail. When the aircraft changed course to 270 degrees (westward), the object suddenly moved at high speed and disappeared in less than a minute.

The aircraft commander, 1st Lt. Robert Arblaster, minimized the sighting. He had looked at the object only briefly and believed it was simply an unusual dark cloud formation detached from the main cloud layer. Because he saw it as a cloud, he did not contact ground control or file a prompt report. The intelligence officer noted that Arblaster had only glanced at the object, whereas the other two crew members had observed it for several minutes and held a different opinion.

Weather personnel from the 2143rd Air Weather Wing suggested the sighting was likely an isolated cloud that appeared dark due to poor lighting or possibly dust or smoke contamination. They noted that weather balloons of various sizes and colors were routinely released in the area. The weather office also observed that several recent unidentified object sightings in the region had occurred when the sun was nearly behind the object, which could have affected observers' perception of movement and speed through changing light conditions.

The Air Force's formal evaluation recorded three possible conclusions: that it was a balloon, that it was probably a balloon, or that it was possibly a balloon. The full case file is reproduced below as held by the National Archives, totaling 15 pages.