Chain Home Low

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Radar Coverage 1939-1940

Chain Home Low (CHL) was the name of a British early warning radar system operated by the RAF during World War II.[1] The name refers to CHL's ability to detect aircraft flying at altitudes below the capabilities of the original Chain Home radars, where most CHL radars were co-located. CHL could reliably detect aircraft flying as low as 500 feet (150 m).

The equipment, technically known as the AMES Type 2, was originally developed for the British Army as a system to detect ships. This requirement had come about when experiments with 1.5 m wavelength air-to-air radar demonstrated the ability to easily pick out ships on the water, leading to developments of additional 1.5 m systems for the "Air-Sea-Vessel" (ASV) and "Coast Defence" (CD) roles. When the Germans accidentally discovered that CH could not see their aircraft at low altitudes, they began a series of low-level attacks that proved almost impossible to defend against. Robert Watson-Watt quickly responded by taking the CD radars that were under construction and shipping them to CH sites, where they were mounted on tall masts and renamed CHL. In keeping with its rapid introduction, CHL was a relatively simple manually-directed system that required the operator to hunt for targets by swinging the antenna back and forth looking for returns. The antenna was originally powered by WAAFs mounted on wheel-less bicycles whose chains were connected to a gear system, but these were later replaced by electric motors.

When first deployed, CHL was used both for early detection of low-level targets, as well as a system for tracking individual aircraft over land; unlike CH which was permanently facing over water, CHL could be turned to look in any direction. This later role became outdated with the introduction of the Type 7 GCI in 1942. Electronically, the Type 7 was essentially a larger and more powerful version of the CHL concept, with a larger ground-level antenna. However, the antenna was continuously spun through a complete circle, and returns were plotted in a map-like form known as a plan-position indicator (PPI). Whereas CHL operators had to calculate a single target's position from the range and bearing, Type 7 operators saw all of the aircraft in their area simultaneously and could determine their map location directly. CHL was increasingly used purely for early warning, calling in the rough location of targets to Type 7 stations who would then know where to look. Later, 3 GHz-frequency Chain Home Extra Low (CHEL) radar were often co-sited with CHL sites, further extending detection as low as 50 feet (15 m).

Several adaptations of the CHL were made during the war. Such systems could be mobile[2] in which units were placed on trucks and could be strategically moved based on enemy movement, giving the RAF a wider option where and when they would engage or not engage the enemy.

Margam CHL Station, 2012

List of Chain Home Low sites[edit]

See also[edit]


  1. ^ "The prototype CH system - 1939... Chain, Home... Operational". Bournemouth University. 1995–2009. Retrieved 23 August 2009. 
  2. ^ "The prototype CH system - Chain Home Low (CHL)". Bournemouth University. 1995–2009. Retrieved 23 August 2009. 
  3. ^ Chain Home Extra Low Station K163, Heritage Gateway. Retrieved 2012-11-01.
  4. ^ TM536881
  5. ^ Anon. "St David's Head". Experience Pembrokeshire. PLANED. Retrieved 21 June 2012. 


  • Batt, Reg., The Radar Army: Winning the War of the Airwaves (1991, Robert Hale, London) ISBN 0-7090-4508-5
  • Bowen, E.G., Radar Days, Institute of Physics Publishing, Bristol, 1987., ISBN 0-7503-0586-X
  • 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 World War II
  • Brown, Louis., A Radar History of World War II, Institute of Physics Publishing, Bristol, 1999., ISBN 0-7503-0659-9
  • 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 World War II told by the men and women who worked on it.
  • Latham, Colin & Stobbs, Anne., Pioneers of Radar (1999, Sutton, England) ISBN 0-7509-2120-X
  • Zimmerman, David., Britain's Shield Radar and the Defeat of the Luftwaffe, Sutton Publishing Ltd, Stroud, 2001., ISBN 0-7509-1799-7

External links[edit]