The authorities, including four local forces and a bomb disposal unit, swung into action after six "flying saucers" were found by members of the public in a perfect line across southern England.
But fears of a real "war of the worlds" incident petered out after examination of the "spacecraft" showed that it was an elaborate rag week hoax by engineering students.
The incident, which was taken seriously for a number of hours, took place in 1967 but has only just been revealed by secret UFO files released by The National Archives.