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Chain Home, or CH for short, was the codename for the ring of coastal Early Warning radar stations built by the British before and during the Second World War to detect and track aircraft. It was one of the first practical radar systems, and the main component of the world's first integrated air defence system.
This station is a Chain Home Low (CHL) which detected enemy aircraft movement at lower altitudes and summarily used with the fixed Chain Home system which was operated by the RAF during World War II.
Chain Home radars stretched across the shoreline of the British Isles, looking outward, offering almost continuous coverage of the over-water areas offshore. CH systems would often detect larger formations while still over France, offering invaluable early warning of an impending raid. The presence of radar strongly swung the balance of power in the direction of defence, it was no longer the case that "the bomber will always get through".