Project 10073 Record Card and Associated Reports — Hokkaido, Japan, February 1958

This document comprises a series of reports and a record card detailing an unusual radar sighting that occurred on February 19, 1958, in the Sea of Japan. Operations personnel at AC&W Site #45 at Asoiwayama, Hokkaido, observed a rapid development of a radar return on their FPS-6 height-finding radar. The return, which was stationary, expanded into a dense cloud approximately 65 miles long and 25 miles wide, rising from an altitude of 3,000 feet to 46,000 feet over the course of two hours. Five Russian aircraft in the vicinity were observed to turn toward the phenomenon. Witnesses, including Captain Henry Kolb and 1st Lieutenant Thomas V. Cole, described the return as resembling the explosion of a large munitions ship. Despite the dramatic nature of the radar return, the report notes that the weather was clear (CAVU) and that there was no evidence of equipment malfunction. Subsequent investigations by the 600th Air Intelligence Service Squadron (AISS) and inquiries with the Japanese Meteorological Agency and the Maritime Safety Board failed to find any barometric or seismic evidence of an actual explosion, despite reports from fishermen regarding luminous sightings in the region. The official conclusion stated that the rapid development and the reaction of the Russian aircraft ruled out natural weather phenomena or radar malfunction, leaving the nature of the event unexplained.