Daventry Experiment
 Type 1 Chain Home Map shows modern aerial photographs of the locations of AMES Type 1 Chain Home. |
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Type 2 Chain Home Low Map shows modern aerial photographs of the locations of AMES Type 2 Chain Home Low. |
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Type 2 Chain Home Extra Low Map shows modern aerial photographs of the locations of Chain Home Extra Low. |
Chain Home, or CH for short, was the codename for the ring of coastal Early Warning radar stations built by the Royal Air Force (RAF) before and during the Second World War to detect and track aircraft. The term also referred to the radar equipment itself, until it was given the official name Air Ministry Experimental Station Type 1 (AMES Type 1) in 1940. Chain Home was the first early warning radar network in the world, and the first military radar system to reach operational status. Its effect on the outcome of the war made it one of the most powerful weapons of what is today known as the "Wizard War".
In 1934, Nikola Tesla, then working in the United States, claimed to have invented a death ray that could destroy aircraft. This was followed by reports suggesting Germany had built some sort of radio-based weapon, and images of a large radio tower in German newspapers. The Tizard Committee was formed to consider the possibility, and asked Robert Watt to comment. Watt's assistant, Arnold Wilkins, calculated a death ray was impossible but suggested radio could be better used for long-range detection. In February 1935, a demonstration was arranged by placing a receiver near a BBC shortwave transmitter and flying an aircraft around the area; an oscilloscope connected to the receiver showed a pattern from the aircraft's reflection. Watt's team quickly built a prototype system using commercial shortwave radio hardware, and on 17 June 1935 it successfully detected an aircraft that happened to be flying by. Basic development was completed by the end of the year, with detection range on the order of 100 miles (160 km). Through 1936 attention was focused on a production version, and early 1937 saw the addition of height finding.
The first five stations, covering the approaches to London, were installed by 1937 and began full-time operation in 1938. Operational tests using early units in 1937 demonstrated the difficulties in relaying useful information to the pilots in fighter aircraft. This led to the formation of the first integrated ground-controlled interception network, the Dowding system, which collected and filtered this information into a single view of the airspace. Dozens of CH stations covering the majority of the eastern and southern coasts of the UK, along with a complete ground network with thousands of miles of private telephone lines, were ready by the time the war began in 1939. The system proved decisive during the Battle of Britain in 1940; CH systems could detect enemy aircraft while they were still forming up over France, giving RAF commanders ample time to marshal their entire force directly in the path of the raid. This had the effect of multiplying the effectiveness of the RAF to the point that it was as if they had three times as many fighters, allowing them to defeat the larger German force. With such high efficiency, it was no longer the case that "the bomber will always get through".
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