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Chain Home tower at Great Baddow

A Grade II Listed Building in Chelmsford, Essex

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Coordinates

Latitude: 51.7074 / 51°42'26"N

Longitude: 0.4976 / 0°29'51"E

OS Eastings: 572665

OS Northings: 203914

OS Grid: TL726039

Mapcode National: GBR PKS.SRZ

Mapcode Global: VHJK8.KBXY

Plus Code: 9F32PF4X+X2

Entry Name: Chain Home tower at Great Baddow

Listing Date: 24 October 2019

Grade: II

Source: Historic England

Source ID: 1456445

Location: Great Baddow, Chelmsford, Essex, CM2

County: Essex

District: Chelmsford

Civil Parish: Great Baddow

Built-Up Area: Chelmsford

Traditional County: Essex

Lieutenancy Area (Ceremonial County): Essex

Summary


Chain Home tower, originally erected at RAF Canewdon in south-east Essex in 1937, relocated to Great Baddow in 1956.

Description

Chain Home tower, originally erected at RAF Canewdon in south-east Essex in 1937, relocated to Great Baddow in 1956.

MATERIALS: galvanised-steel frame; timber and steel mesh flooring to the mid-level platforms; reinforced-concrete foundation pads.

PLAN: rectangular in plan.

DESCRIPTION: a Group II self-supporting transmitter tower, originally built by Radio Communication Ltd, based on an Air Ministry design by Mr Norman Garnish. The tower is of bolted galvanised-steel construction, attached to four reinforced-concrete foundation pads. It stands approximately 109.12m high, with three pairs of cantilevered working platforms at low (15.2m), mid- (62.2m) and high (107.9m) levels. The mid-level has timber flooring to its north platform, and late-C20 wire mesh flooring to its south platform; the flooring material of the low-level platforms has been removed. The metal ladder and landing stages, of which there are approximately 12, were replaced in the late C20.

Three detached single-storey huts stand under the tower, and the site is bounded by a late C20 or early C21 wire-mesh and barb-wire fence; both are excluded from the listing.

History

Guglielmo Marconi established the Wireless Telegraph and Signal Company in 1897, and in 1898 acquired a former silk mill in Chelmsford for the manufacture of Marconi radio equipment. During the First World War (1914-18), the research department of the Marconi Company was placed under the direction of the Admiralty, and 415 ships and 30 shore stations were equipped with wireless sets. The Marconi Company played a key role in the development of telephony and radar during the First World War and inter-war period. The company moved in to public broadcasting, with the first official radio broadcast from Chelmsford in June 1920, and took part in the formation of the British Broadcasting Company in 1922. By the early 1930s, Marconi was one of the principal suppliers of telephones, telegraph and wireless equipment to the British services, armed forces abroad, and civilian aerodromes. Under the trade name Marconiphone, the company was also a leading manufacturer of wireless sets for the domestic market, however sold this interest to the Gramophone Company in 1929. The Marconi research laboratories at Chelmsford continued to expand, and a decision was made in 1936 to acquire a large site on a hill at Great Baddow on the outskirts of Chelmsford, which was deemed sufficiently far away from possible sources of interference to conduct experiments. The laboratories at Great Baddow were constructed between 1937 and 1939, with a red brick laboratory building facing east to West Hanningfield Road (not listed).

Radio direction finding (later known as radar) was a well-established technique by the 1930s and widely used in civil as well as military applications for ship and aircraft navigation, utilising reflected radio waves to detect the approach of hostile craft. Robert Watson Watt and Arnold Wilkins carried out pioneering research at nearby Bawdsey Manor leading to the inception of the ‘Chain Home’ network, the first early warning radar network in the world, and the first military radar system to reach operational status. The siting of the Chain Home stations was of crucial importance to their successful operation; the specifications issued in 1936 required that a station should be well back from the coast, with a smooth slope between it and the sea, give good height and range finding, and be inconspicuous from the air. The first five stations, the (Thames) Estuary Chain, covered the approaches to London, and were used for system trials in 1937 before becoming fully operational in 1938. One of these five early stations was at RAF Canewdon in south-east Essex, established in August 1937, with three Chain Home towers providing long-range early warning for the Thames estuary and the north-eastern approaches to London. Twenty-one Chain Home stations were established along the south and east coasts of England during the Second World War (1939-45).

Initially, the transmitter aerials were suspended on 358ft self-supporting steel towers, between three working platforms on each side, cantilever to cantilever, but from 1941 the aerial arrays were suspended between the adjacent towers. Chain Home RDF (radar) stations did not sweep a rotating radar beam, but irradiated lobes of energy along a particular bearing or ‘line of shoot’. Due to the shape of the main lobe, it was not possible to provide total coverage without a number of secondary lobes to ‘gap-fill’ the sides. The main lobes of the adjoining CH stations at RAF Great Bromley and RAF Dunkirk partially intersected that of RAF Canewdon, to produce continuous cover over the Thames Estuary. The plots of the same aircraft from the adjacent Chain Home stations were all sent to the ‘Filter Room’ at Fighter Command Headquarters, RAF Stanmore, where they could be filtered to provide a smooth course plot; data was also fed directly to the nearest Sector Operations Room, within the associated Fighter Group. The ‘Final’ Chain Home stations provided long-range, early warning of enemy aircraft, with an average range of between 160.93 - 321.86km (100 – 200 miles), on aircraft flying at 4,572m (15,000ft), but were unable to detect aircraft flying below 60.9m (200ft). The Chain Home RDF stations were decisive in providing early warning of Luftwaffe attacks, and the towers at RAF Canewdon played a particularly crucial role in the air defence of the country during the Battle of Britain and in the defence of London throughout the Second World War, including the late war V1 flying-bomb campaign and the ‘Big Ben’ V2 missile tracking operations. Post-war, the radar equipment at RAF Canewdon quickly became obsolete and was not updated, resulting in the site not being included in the ROTOR radar reporting system; however, the northernmost tower remained in use for RAF aerial erector training purposes and for climbing tests until 1956.

The scientists at the Great Baddow laboratories designed the transmitter aerials for the Chain Home system, and at the outbreak of the Second World War, many of the Marconi Company’s scientists and engineers were seconded to government research establishments. At Great Baddow, the Royal Air Force was engaged in research on radio propagation from 1940, and the Royal Navy was carrying out research under the Admiralty Signal Establishment from 1941. Most of the research work at Great Baddow related to the development of radio technology, and included system design, growing synthetic quartz crystals, and techniques such as direction finding linked with propagation. Used in aircraft, ships and mobile equipment, this technique could be used during warfare to identify the source of enemy agents’ radio transmissions. During the Second World War, other important activities at the Great Baddow site included the engineering of aerial, receiver and display units for the 960 naval radar, and early production of the resonant cavity magnetron, a vital breakthrough in radar technology.

In the late 1940s Britain’s wartime radar system was substantially updated to meet the threat posed by fast jet aircraft. The Marconi Company became a subsidiary of English Electric in 1946, and the Great Baddow site became a recognised source of expertise on all aspects of radar research, including the study of wartime radar chain, which became urgent with the blockade of West Berlin in 1948 and the invasion of South Korea in 1950. During the 1950s, small scale buildings and masts were built at Great Baddow for the experimental testing of radio, radar and telecommunications equipment, most significantly the development of the radio guidance system for the British 'Blue Streak' intercontinental ballistic missile, developed between 1955 and 1957. In 1956, the Marconi Company purchased one of the (then obsolete) towers from Canewdon in south-east Essex, and transported it to and re-erected it on the Great Baddow site the same year. The 1970 Ordnance Survey (OS) map shows the tower in its current position with a rectangular-plan hut underneath, laid out on an east-west axis. Additional buildings were constructed to the rear (west) of the 1930s building between 1957 and 1958 to the designs of Taylor and Collister. The Marconi Company became the primary defence subsidiary of the General Electric Company (GEC) around 1968, becoming GEC Marconi. In 1999, the defence manufacturing division, Marconi Electronic Systems, merged with British Aerospace to form BAE Systems, who still occupy the majority of the site.

The tower at Great Baddow is the only complete Chain Home transmitter tower surviving in the British Isles, standing to its full height of 109.12m (358 feet) and retaining all six working platforms. Three listed towers survive: one at Stenigot, Lincolnshire (listed Grade II); Dunkirk, Kent (listed Grade II); and Swingate, Kent (listed Grade II*); however, none of these retain all of their working platforms and one has been truncated. A listed example at Bawdsey, Suffolk and a second tower at Swingate, Kent were condemned as unsafe and demolished in the early C21. Three other Chain Home towers are known to survive in the British Isles, but none are as complete as the tower at Great Baddow: a Group II tower standing to full height at Great Bromley, Essex, minus its working platforms; and two severely truncated examples, one situated at Elsham Wolds, Lincolnshire and the other at Watton, Norfolk.

Reasons for Listing

Great Baddow Chain Home Tower, originally erected at RAF Canewdon in south-east Essex in 1937, relocated to Great Baddow in 1956, is listed at Grade II for the following principal reasons:

Architectural interest:
* the tower at Great Baddow is the only complete Chain Home transmitter tower surviving in the British Isles, standing to its full height of 109.12m (358 feet) and retaining all six working platforms.

Historic interest:
* the Chain Home Radio Direction Finding stations were decisive in providing early warning of Luftwaffe attacks, and the towers at RAF Canewdon played a particularly crucial role in the air defence of the country during the Battle of Britain, and in the defence of London throughout the Second World War, including tracking of destructive V1 flying bombs and “Big Ben” V2 missiles late in the war;
* although the tower was moved to its current location in 1956 this contributes to, rather than detracts from, its special historic interest. Its relocation to the Marconi Company research site at Great Baddow provided a context in which the tower could play an important defence role during the Cold War. During this period Great Baddow tower continued to play an important role in defence research and communications, in particular the development of the radio guidance system for the British 'Blue Streak' intercontinental ballistic missile.

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