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Summary: RAF instructional film illustrates the practical use of echo location.
Description: Animated diagrams and a commentary explain how mass numbers of aircraft are counted by means of echo responses emitted from CH (Chain Home) stations. As formation of enemy planes cross the Channel to attack Britain, targets appear on a screen and are interpreted. Actual filmed record of this system in operation on 25 August 1940 and 26 September 1940 show the packed formations of enemy planes (as recorded by targets on the screen) split up into separate sections as the air battles reach their height. After the battle, only a few targets remain.