Bornholm, Denmark, August 1956August 1956

On August 22, 1956, radar operators at Bornholm, a Danish island in the Baltic Sea, detected several unidentified objects moving at very high speeds. The first targets appeared around 2050 hours (8:50 p.m.) on a radar scope, with 2 to 3 objects reported initially, later increasing to 4. All objects were traveling at approximately 700 knots (roughly 800 mph) at an altitude of 25,000 feet. What made the sighting unusual was that after about three hours, the objects began orbiting over a fixed location near the radar station (coordinates 53 degrees 30 minutes north, 18 degrees east) before all tracks faded from the scope at approximately 2309 hours (11:09 p.m.).

The Air Force investigators who reviewed the case noted several possibilities. The objects' ability to orbit at such high speeds made them unlikely to be Soviet guided missiles, since that behavior did not match known missile test patterns. However, the file reveals that most of the evidence pointed toward a natural explanation. Radar operators and analysts suspected the targets might have been caused by unusual weather conditions, specifically what they called anomalous propagation. When temperature inversions (layers of warm air trapping cooler air below) form over water, they can bend radar beams downward, causing them to pick up objects on the ground or sea and display them as targets in the air. The appearing and disappearing nature of the tracks on the radar scope, and the fact that all targets vanished simultaneously, fit this explanation well.

The Air Force requested additional data from the Bornholm radar station, including detailed weather information, radar scope photographs, and precise timing and altitude readings. Without these details, the investigators stated they could not reach a firm conclusion about the sighting's nature. A memo sent to Air Force leadership in October 1956 confirmed that all available evidence strongly supported the anomalous propagation theory, though uncertainty remained due to incomplete information.

The full case file, comprising 21 pages as held by the National Archives, is reproduced below.