[ILLEGIBLE], April 1950April 1950

On April 27 and 28, 1950, two Air Force pilots flying F-80C jet fighters near Misawa Air Base in Japan reported seeing unidentified objects while flying at altitudes between 18,000 and 30,000 feet. Both incidents were documented in official intelligence reports and prompted investigation by the Fifth Air Force.

On the first occasion, April 27 at 1:45 p.m., a pilot was joining his element leader over Camp Haugen when he spotted what appeared to be a target being towed behind the lead aircraft. The object was rectangular, about sixty feet long and twenty feet high, and appeared to be made of muslin fabric with an orange tint. It showed no evidence of propulsion or exhaust. The pilot maneuvered to get a better look and kept the object in sight for about two and a half to three minutes, watching from above and both sides. The object seemed to track the lead aircraft, accelerating from roughly 275 to 300 mph up to an estimated 600 mph before breaking away and disappearing.

The second sighting occurred on April 28 at 12:30 p.m., when a different pilot observed a square-shaped white object about twelve feet on each side while flying near Wakkanai at 30,000 feet. The pilot saw it traveling at 600 to 650 mph, moving through the clouds. He descended to 18,000 feet and searched the area for fifteen minutes. The radar site tracking the pilot during this time reported no signal from any unidentified object.

In a formal memorandum to General Cabell, Air Force intelligence analysts concluded that the objects were not aircraft or aerodynamic devices, but rather visual effects produced by shock waves from other F-80C jets in the area. They theorized that the effects could result from light refraction caused by shock waves (a phenomenon called Schlieren effect), ice crystals formed when shock waves disturbed supercooled water vapor, polarization of light, or a combination of these conditions. The analysts noted that the descriptions of the objects having "no density" and looking like fabric, with no obvious reflecting surfaces, suggested not a solid object but a "condition" in the air rather than a physical thing. They compared the incidents to unexplained "explosions" previously observed near Dayton that had been attributed to jet aircraft shock waves.

The full case file, containing 9 pages as held by the National Archives, is reproduced below.