North Truro, Mass, October 1951October 1951

On October 22, 1951, a radar station at North Truro, Massachusetts, picked up an unusual object moving across its radar scope. The station's radar operators tracked the target for four minutes as it moved generally east and then south, at an estimated speed of 2,400 miles per hour. The object was detected 120 to 300 miles away from the station. The radar signal showed a distinctive sausage shape, typical of a streamlined aircraft, and individual returns varied in strength as the signal moved across the scope. The object eventually faded from the radar screen about 30 miles north of the station, though the reason remains unclear (it could have descended into the ocean or climbed to an extremely high altitude).

The Air Force investigation, documented in these records, considered several explanations. Weather conditions at the time did not support temperature-inversion anomalous propagation, a known source of false radar returns. However, the file suggests that meteors entering Earth's atmosphere may have caused ionization that made them visible to radar. A meteor entering the atmosphere would create conditions matching the observed short duration of the signal. The Air Force also noted that unusual atmospheric conditions beyond those measured could potentially explain the radar echo through anomalous propagation, or that an unconventional flying object could not be ruled out. Ultimately, the investigators stated there was insufficient data regarding track direction, range, and other variables to reach a definitive conclusion.

This case is preserved in 23 pages of declassified material held by the National Archives.