What happened
In September 1952, NATO held Exercise Mainbrace in the North Sea and Scandinavia, involving tens of thousands of personnel and hundreds of ships and aircraft. On September 19, RAF aircrew at Topcliffe in Yorkshire, including officer John Kilburn, saw a silvery, round object at an altitude of about 4.5 kilometers that seemed to be following a Gloster Meteor fighter. The object stopped, began swinging like a pendulum, and then flew off at high speed. Personnel at nearby RAF Dishforth saw a similar disc. On the same day, Danish airmen reported a silver disc over the North Sea. British newspapers carried the reports on their front pages, and the case also made its way into the archives of the American Project Blue Book.
Witnesses
RAF aircrew at Topcliffe, among them officer John Kilburn, and personnel at nearby RAF Dishforth.
Explanations and hypotheses
The British Air Ministry offered no explanation. Skeptics suggested a weather balloon or a reflection of the sun, but the witnesses emphasized the object’s rapid maneuvers and sudden acceleration. The sightings during Exercise Mainbrace are sometimes cited as one of the reasons the British military began to take UFO reports more seriously and collect them systematically.
Disputed A likely explanation exists, but some of the facts are still disputed.
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