OSCEALA, WISCONSINJuly 1952

On July 29, 1952, radar operators at a U.S. Air Force station near Osceola, Wisconsin detected multiple unidentified objects moving across their scope over the course of an hour. The sighting consisted of two distinct patterns. One large, well-defined target traveled at about 600 knots (roughly 690 miles per hour) across the scope set on the 50-nautical-mile range. The second pattern involved multiple smaller targets (sometimes numbering up to ten) that appeared in a loose cluster, moving at 50 to 60 knots.

The targets had distinctive behavior. All appeared suddenly on the radar scope and disappeared just as abruptly after traveling between 30 and 70 nautical miles. They generally moved from southwest to east across the scope, though individual targets within the clusters moved independently of each other and made turning movements. The Air Force crew tilted the radar antenna to minimize anomalous propagation (a false radar echo caused by unusual weather), adjusting between 5 and 9 degrees during the sighting period.

In response to these radar contacts, an F-51 fighter aircraft from the 125th Fighter Interceptor Squadron was scrambled. The pilot reported visually sighting what he described as objects resembling "stars or comets with tails" at several points during his patrol of the area east of St. Paul and south of the radar station. However, he was unable to identify or intercept them. The pilot was flying at 25,000 feet and estimated the objects he saw were at approximately 125,000 feet, though this extreme altitude estimate raised questions about reliability. Weather in the sighting area was reported as clear and unlimited visibility, with no lightning flashes or other interference reported.

The Air Technical Intelligence Center (ATIC) noted that anomalous propagation could account for ground clutter on the radar scope, but added that such a condition alone would not explain the apparent movement of targets unless weather was disrupting the antenna sweep in a way that made stationary ground targets appear to move. The file indicates that a complete analysis could not be made without temperature and humidity data that was not available. The Air Force concluded the case "Unknown," unable to explain either the radar contacts or the pilot's visual sightings on the basis of available evidence.

The full case file is reproduced below as held by the National Archives across 39 pages.