Minneapolis, MinnesotaOctober 1951

On the morning of October 11, 1951, a research aircraft crew flying near Minneapolis spotted something unusual in the sky. The pilots were at 10,000 feet, observing a weather balloon, when they saw a brightly glowing object to the southeast. The object was moving rapidly from east to west at a very high altitude, crossing the sky at roughly 20 degrees per second. It had a peculiar appearance, with what looked like a halo around it and a dark underside. After moving fast, the object slowed down and began climbing in lazy circles, its path resembling a falling oak leaf turned upside down. The pilots watched it for about five minutes before it accelerated rapidly and disappeared to the east. Shortly after this sighting, they spotted a second similar object, which approached from the west and then vanished to the east.

Neither object left a vapor trail. When the pilots radioed the tracking station at the University of Minnesota airport, ground observers aimed a theodolite (a surveying instrument used to measure angles) at the objects but could not keep the instrument moving fast enough to follow them. The ground team did manage brief glimpses, describing what they saw as a smoky grey, cigar shaped object with no visible halo or glow. They noted it left no vapor trail and reflected no light.

The men who reported the sightings were experienced observers. Most were research engineers working on classified projects for General Mills and also served as pilots. One of them had flown fighter planes during World War II. The Air Force investigators emphasized the reliability of these witnesses and their knowledge of aircraft and balloons. Yet after further investigation, no one could identify what the objects were. The observers were certain the objects were not balloons, jets, conventional aircraft, or stars. The Air Force concluded that the objects remained unidentified. The full case file is reproduced below as held by the National Archives, comprising 15 pages.