Michigan - Wisconsin, September 1951September 1951

On September 18, 1951, radar operators at Air Defense Command stations across Michigan and Wisconsin detected unusual blips moving rapidly across their screens. The objects appeared on radar as oblong shapes, similar to large aircraft but noticeably bigger. Over the course of roughly three hours, from about 10:35 a.m. to 1:35 p.m., operators tracked multiple radar contacts moving through the region north of major cities like Milwaukee and Detroit.

The radar blips showed extreme speed, with estimates reaching 6,000 miles per hour. The objects' altitude could not be determined because of how fast they were moving. The radar stations that detected them, located at positions called P-31 and P-34, tracked the targets as they moved across a wide area: from near Milwaukee to near Selfridge Air Force Base, then northwest toward Sault Ste. Marie, east toward Bay City, and back southeast toward Port Huron. Experienced radar operators at both stations observed the blips.

The Air Force scrambled two F-86 fighter jets from Oscoda Air Force Base to intercept the objects, but they had no luck finding anything. A neighboring radar station also picked up similar targets, though the tracks appeared scattered and dispersed.

The investigation focused on weather conditions at the time. Heavy ground fog with high moisture content blanketed the entire area during the sighting, moving north and east as the hours passed. An observatory in Wisconsin reported that observations had not been made that evening because of a 200-foot-thick layer of ground fog. The Air Force concluded that the radar blips were probably caused by ducting, a weather phenomenon in which layers of air at different temperatures bend radio waves in unusual ways, creating false radar returns. This effect had supposedly occurred before in similar foggy conditions, though the investigators noted no other physical evidence supported the conclusion.

The full case file is reproduced below as held by the National Archives, comprising 7 scanned pages.