• Chain Home Radar
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.
From the earliest days of radio technology, signals had been used for navigation using the radio direction finding (RDF) technique. RDF can determine the bearing to a radio transmitter, and several such measurements can be combined to produce a radio fix, allowing the receiver's position to be calculated. Through the early period of radio development it was also widely known that certain materials, especially metal, reflected radio signals. This led to the possibility of determining the location of objects by broadcasting a signal and then using RDF to measure the bearing of any reflections. The use of radio detection specifically against aircraft was first considered in the early 1930s. Teams in the UK, US, Japan, Germany and others had all considered this concept and put at least some small amount of effort into developing it. Lacking ranging information, such systems remained of limited use.
In 1932, Winston Churchill and his friend, confidant and scientific advisor Frederick Lindemann travelled by car in Europe, where they saw the rapid rebuilding of the German aircraft industry. It was in November of that year that Stanley Baldwin gave his famous speech, stating that "The bomber will always get through". In the early summer of 1934, the RAF carried out large-scale exercises with up to 350 aircraft. The forces were split, with bombers attempting to attack London, while fighters, guided by the Observer Corps, attempting to stop them. The results were dismal. In most cases, the vast majority of the bombers reached their target without ever seeing a fighter. The numbers suggested any targets in the city would be completely destroyed. Through the early 1930s, a debate raged within British military and political circles about strategic air power. Baldwin's famous speech led many to believe the only way to prevent the bombing of British cities was to make a strategic bomber force so large it could, as Baldwin put it, "kill more women and children more quickly than the enemy." As it became clear the Germans were rapidly rearming the Luftwaffe, the fear grew RAF could not meet the objective of winning such a tit-for-tat exchange.
The need to research better forms of air defense prompted Harry Wimperis to press for the formation of a study group to consider new concepts. Lord Londonderry, then Secretary of State for Air, approved the formation of the Committee for the Scientific Survey of Air Defence in November 1934, asking Henry Tizard to chair the group, which thus became better known to history as the Tizard Committee. In August 1935, Albert Percival Rowe, secretary of the Tizard Committee, coined the term "Radio Direction and Finding" (RDF), deliberately choosing a name that could be confused with "Radio Direction Finding", a term already in widespread use. The system was deliberately developed using existing commercially available technology to speed introduction.
During the summer of 1936, experiments were carried out at RAF Biggin Hill to examine what effect the presence of radar would have on an air battle. Assuming RDF would provide them 15 minutes warning, they developed interception techniques putting fighters in front of the bombers with increasing efficiency. They found the main problems were finding their own aircraft's location, and ensuring the fighters were at the right altitude. By the outbreak of war in September 1939, there were 21 operational Chain Home stations. After the Battle of France in 1940 the network was expanded to cover the west coast and Northern Ireland. The Chain continued to be expanded throughout the war, and by 1940 it stretched from Orkney in the north to Weymouth in the south. This provided radar coverage for the entire Europe-facing side of the British Isles, able to detect high-flying targets well over France. The rapid expansion of the CH network necessitated more technical and operational personnel than the UK could provide, and in 1940, a formal request was made by the British High Commission, Ottawa of the Canadian Government, appealing for men skilled in radio technology for the service of the defence of Great Britain. By the end of 1941, 1,292 trained personnel had enlisted and most were rushed to England to serve as radar mechanics. During the Battle of Britain, Chain Home stations – most notably the one at Ventnor, Isle of Wight — were attacked several 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 open steel girder construction. Because the towers survived intact and the signals were soon restored, the Luftwaffe concluded the stations were too difficult to damage by bombing and left them alone for the remainder of the war.
Chain Home was the primary radar system for the UK for only a short time. By 1942, many of its duties had been taken over by the far more advanced AMES Type 7 GCI radar systems. Whereas CH scanned an area perhaps 100 degrees wide and required considerable effort to take measurements, the Type 7 scanned the entire 360-degree area around the station, and presented it on a plan position indicator, essentially a real-time two-dimensional map of the airspace around the station. With the deployment of GCI, CH became the early warning portion of the radar network. To further simplify operations and reduce manpower requirements, the job of plotting the targets became semi-automated. An analogue computer of some complexity, known simply as "The Fruit Machine", was fed the bearing and range directly from the operator console, reading the goniometer setting directly, and the range from the setting of a dial that moved a mechanical pointer along the screen until it lay over a selected target. Late in the war, when the threat of Luftwaffe bombing had ended, the CH systems were used to detect V2 missile launches. After the war, they were reactivated as part of the ROTOR system to watch for Soviet bombers, before being replaced by newer systems in the 1950s. Today only a few of the original sites remain intact in any fashion.
