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Chain Home

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Marconi tower at sunset.

Chain Home / AMES TYPE 1 (Air Ministry Experimental Station) was the codename for the ring of coastal radar stations built by the British before and during World War II. The system comprised two types of radar: the metre-wave Chain Home stations which provided long-range early warning, and the centimetre-wave Chain Home Low / AMES TYPE 2 stations, which were shorter-ranged but could detect aircraft flying at low level.

Overview

From May to August 1939, LZ130 German Zeppelin were performing flights near Great Britain's coastline, where their goal was to confirm the theory that the 100 m high towers that the British had erected from Portsmouth to Scapa Flow were used for aircraft radio-localisation. LZ130 performed a series of tests, from radiowave interception, through magnetic and radio frequency analysis to taking photographs. However, the poor quality of the German equipment resulted in their failure to detect operational British Chain Home radar, and thus the LZ130 mission concluded that the British towers were not connected to radar operations, but rather formed a network of naval radiocommunication and rescue.

The Chain Home stations were arranged along the British coast, initially in the south and east of England, but later throughout the entire coastline, including the Shetland Islands. They were first tested in the Battle of Britain in 1940 when they were able to provide adequate early warning of incoming Luftwaffe raids.

The Chain Home system was very primitive, and in order to be ready for battle it had been rushed into production by Sir Robert Watson-Watt's Air Ministry research station near Bawdsey. Watson-Watt, a pragmatic engineer, believed that "third-best" would do if "second-best" would not be available in time and "best" never available at all. Chain Home was certainly a "third-best" system and suffered from glitches and errors in reporting. However, it was still the best in the world then available and provided critical information without which the Battle of Britain might have been lost.

Chain Home looked nothing like the popular image of a radar. Unlike the German radars, there was no rotating antenna sending out a "searchlight" beam of radio energy while watching for echoes. Chain Home had only fixed antennas. The transmitting array sent out a "floodlight" of radio energy, covering a swath of about 100 degrees. The receiving array consisted of two antennas fixed at right angles to each other. These antennas were directional in their sensitivity, and depending on the angle the target was from them, an echo would affect one more than the other. An operator would manually adjust a comparator circuit to find which angle best matched the relative strengths of the received echo signals. The angle of elevation to the target was estimated by comparisons to the signal strength of a second set of receiving antennas located closer to the earth. The time delay of the echo, of course, determined the range.

During the battle, Chain Home stations, most notably the one at Ventnor, Isle of Wight, were attacked a number of times between 12 and 18 August, 1940. On one occasion a section of the radar chain in Kent, including the Dover CH, was put out of action by a lucky hit on the power grid. However, though the wooden huts housing the radar equipment were damaged, the towers survived owing to their steel girder construction. Because the towers were untoppled and the signals soon restored, the Luftwaffe concluded the stations were too difficult to damage by bombing and so left them alone for the rest of the war. Had the Luftwaffe realised just how essential the radar stations were to British air defences, it is likely that they would have gone all out to destroy them.

The Chain Home system was dismantled after the war, but some of the tall steel radar towers remain, converted into new uses for the 21st Century.

One such 360-foot-high (110 m) transmitter tower (picture above) can now be found at the BAE Systems facility at Great Baddow in Essex (2003). It originally stood at Canewdon, and is said to be the only Chain Home tower still in its original, unmodified form.

Compare to the German Freya radar.

Interestingly, the Germans deployed a simple radar system, the Kleine Heidelberg Parasit, which allowed them to track British aeroplanes using the radio signals from the British Chain Home radars. The "floodlight" nature of the Chain Home transmissions would provide a pair of signals which could be used to locate aircraft. The primary signal was the direct flight of the radio signal from the Chain Home transmitter to the German receiver. The second, weaker signal was that reflected from the aircraft. The time delay between these two signals established how much longer was the reflected path compared to the direct path. From geometry, this longer path length described an ellipse on which the aircraft must lie. The focal points of this ellipse were the transmitting and receiving antennas, and the Germans knew the location of both. A simple direction finding antenna searching for the echo could be used to establish where on the ellipse the aircraft was. This system gave the Germans a radar with a range of up to 400 km and an accuracy in range of 1 to 2 km and in bearing of about 1 degree.[1]

Chain Home / AMES Type 1 Sites

See also

Notes

  1. ^ Pritchard, David, The Radar War, Patrick Stephens Limited, Wellingborough, 1989, ISBN 1-85260-246-5

Further reading

  • Bragg, Michael., RDF1 The Location of Aircraft by Radio Methods 1935-1945, Hawkhead Publishing, Paisley 1988 ISBN 0-9531544-0-8 The history of ground radar in the UK during WWII
  • Latham, Colin & Stobbs, Anne., Radar A Wartime Miracle, Sutton Publishing Ltd, Stroud 1996 ISBN 0-7509-1643-5 A history of radar in the UK during WWII told by the men and women who worked on it.
  • Zimmerman, David., Britain's Shield Radar and the Defeat of the Luftwaffe, Sutton Publishing Ltd, Stroud, 2001., ISBN 0-7509-1799-7
  • Brown, Louis., A Radar History of World War II, Institute of Physics Publishing, Bristol, 1999., ISBN 0-7503-0659-9
  • Bowen, E.G., Radar Days, Institute of Physics Publishing, Bristol, 1987., ISBN 0-7503-0586-X
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