Chain Home Radar

Background

By the 1930’s, many countries were researching into the possibilities. The British Army Signal Corps had an interest in 1931, but abandoned it.  Germany in particular had been working on radio reflections since at least 1929, and produced their Freya radar which was much better than the first British coastal radars, and about a year earlier.  There was a chain of them along the German North Sea coast at the outbreak of the second war.

In Britain Sir Robert Watson Watt was asked informally by a member of a Government Committee if there was anything in a proposed “death ray” idea as an anti aircraft defence.  He referred the question to Arnold Frederick Wilkins who easily calculated that it was a hopeless prospect, but suggested that the known phenomenon of aircraft disturbing the transmissions of nearby radio stations was a much more promising means of detection, rather than destruction, of approaching aircraft.  Wilkins’ distinction between detection and destruction seems almost certain to have initiated the radar thought process in this country.  Sir Robert’s paper, dated 12th February 1935 entitled “Detection and Location of Aircraft by Radio Methods”, is a classic of its kind, demonstrating how aircraft could be both detected and located by radio methods, and even identified as friend or foe.

The Government asked for a demonstration, and Sir Robert took senior people to a field near the large civilian radio transmitter at Daventry where a test, designed and conducted by Wilkins, amply demonstrated aircraft interfering with Daventry's transmissions. Money for research was provided.

Sir Robert, rapidly set up a small unit on the Suffolk coast. Within days, in June 1935, they were following aircraft out to 15 miles, and by March 1936, only 13 months after the initial paper, they were working at ranges of 80 miles.  They used existing radio techniques, and little was novel.   For example, their design simply  "floodlit" with pulsed radio waves a sector of about 120 degrees from a fixed transmitter.  Direction finding was obtained from the returning echo by crossed aerials and a goniometer.   A chain of these elementary “CH” (for Chain Home) stations was erected up the East coast, under Wilkins’ supervision and under very great pressure of time, where they and their associated reporting system proved vital in the Battle of Britain in 1940.   Sir Robert and his colleagues would surely have known that they could build a much better radar than that, but there was no time.  War was imminent, and what was known to work was applied.  Refinement could (and did) come later.

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