Mankato, MinnesotaNovember 1951

On November 24, 1951, two Air Force F-51 fighter pilots flying a combat air patrol south of Minneapolis saw something unusual at 25,000 feet. While heading west under radar control, the flight leader spotted a small, milky white object shaped like a flying wing. The object appeared to be roughly eight feet across and seemed to be hanging motionless in the air, heading east.

The sighting lasted about five seconds. The object passed approximately 100 feet above and 100 feet to the left of the lead aircraft. The wingman, flying on the left wing, did not see the object. There was no sound, no exhaust trail, and the speed could not be determined. The object eventually disappeared in the distance. After the sighting, the pilots made a 180-degree turn in an attempt to catch or see the object again, but the effort was unsuccessful.

The investigation that followed checked several possibilities. Air traffic controllers at Minneapolis confirmed that the ground radar had picked up nothing besides the two F-51s. The Minneapolis Air Route Traffic Control Center reported that a weather balloon had been released from the University of Minnesota airport about two hours before the sighting, but it had landed 250 miles to the southeast, making it an unlikely candidate. The Air Force also checked with Lowry Air Force Base to see whether any classified aircraft had been reported in the area during the previous 24 hours, but received a negative response. Weather conditions were clear with visibility of about 50 miles.

The Air Force concluded that no meteorological activity or other condition could account for the sighting. No physical evidence was recovered. The officer who filed the report considered the pilot observer to be fairly reliable. The Air Force's official evaluation was "unidentified," though the cover sheet also noted "probably balloon" as a possible explanation. The full case file is reproduced below as held by the National Archives, comprising 8 pages.