Itazuke AB, Japan, December 1956December 1956

On December 17, 1956, two U.S. Air Force pilots were practicing radar intercept maneuvers near Itazuke Air Base in Japan when one of them detected an unusual radar signal. The lead pilot picked up a radar blip roughly 20 miles away on his scope, estimated to be as large as a B-29 four-engine bomber based on the size of the signal. When he closed in to within eight miles, he saw a round, tan-colored object in the sky, flat on the bottom and round on top, at exactly the location his radar indicated. The trailing pilot, flying six miles behind, did not detect the object on his radar or see it visually.

As the lead pilot approached, his radar locked onto the target and showed he was closing at about 600 to 700 knots (roughly 720 to 840 miles per hour). At one point, the pilot's radar experienced strong interference that resembled electronic countermeasures (ECM, a technique used to jam radar). The pilot switched frequencies to recover the signal, which worked temporarily. The jet managed to close to within five nautical miles of the object, but could not get any closer. The pilot described the object as making a shallow left turn just before its radar signature suddenly accelerated rapidly upward on the scope. The object vanished from radar at about 12 miles distance, with the pilot estimating its final speed at 1,500 to 1,800 knots (roughly 1,800 to 2,160 miles per hour) as it departed. The visual observation lasted three to four minutes, while the radar contact persisted for seven to eight minutes.

The Air Force investigation produced conflicting analysis. One report suggested the radar return was a spurious target or false echo, possibly caused by atmospheric interference, and that the visual sighting was a weather balloon. The file notes that several types of weather balloons, including radiosondes and pibals (all tan or golden-colored), were routinely launched in the area, and unusual wind currents or atmospheric conditions could cause them to appear to maneuver. Another analysis raised doubts about the radar explanation, noting that the size of the blip was unusually large, that neither the trailing pilot nor the ground control station detected the target, and that the extreme closing speed did not match any known aircraft. An intelligence officer reviewing the case suggested that unusual weather or transmission conditions might affect both radar and visual observations, creating a false association between a real visual object and a false radar blip.

The file indicates no firm conclusion was reached. The radar sighting was officially evaluated as unknown, while opinions within the Air Force ranged from weather balloon to spurious radar return to a genuine but unexplained object. The case file comprises 12 pages as held by the National Archives.