Chain Home was the title given to the radar defence established in Britain in the years and days that led to the Battle of Britain in 1940. Chain Home along with Chain Home Low provided Fighter Command with its early warning system so that fighter pilots could get airborne as early as was possible to combat incoming Luftwaffe aircraft.
The original chain of RDF stations (Radio Direction Finding – the term ‘radar’ was not adopted until 1943) consisted of 21 stations. They were built from Southampton to the Tyne and the first was finished at Bawdsey in 1936, which also served as a radar training school. It was handed over to the RAF in May 1937. The radar station at Dover was handed over in Jul 1937. Both became operational in 1938. By the start of the war, RAF aircraft had been fitted with IFF – ‘Identification Friend or Foe – which allowed each station to know whether what they were ‘seeing’ was friendly or not.
Chain Home radars had the ability to detect incoming aircraft at a variety of heights and distances. Targets that flew at 1000 feet could be detected at a distance of 25 miles; targets that flew at 2000 feet could be detected at a distance of 235 miles; targets that flew at 5000 feet could be detected at a distance of 50 miles; targets that flew at 13,000 feet could be detected at a distance of 83 miles.
Chain Home was helped by Chain Home Low. Thirty of these smaller stations were placed either on high ground, such as the North Downs, or on the coast. Those on the coast were very open to attack and were frequently the victims of attacks by Stuka dive-bombers. Chain Home Low used a narrow searchlight beam that was useful against low-level flights but over a shorter distance.
Chain Home and Chain Home Low were connected by telephone and were able to exchange information and data as well as pass it on the ‘Filter Room’ at Fighter Command. By using information from Chain Home, Chain Home Low and the Observer Corps, Fighter Command had as much information as could have been acquired in such a situation using the technology that was available.
The information provided to Fighter Command was vital. Chain Home could detect Luftwaffe squadrons as they gathered over the coast of Northern France. Chain Home Low could detect aircraft flying low enough to avoid detection by Chain Home. With such information, Fighter Command usually had about 20 minutes to put fighter squadrons in the air. Timing was vital as both Hurricane and Spitfire pilots preferred to attack from on high as height gave them the advantage over the enemy. A Spitfire needed 13 minutes to scramble and then get to its preferred flying height of 20,000 feet. A Hurricane needed slightly longer – 16 minutes. Therefore the 20 minutes given to them by Chain Home usually allowed Fighter Command to get into a more advantageous position.
The work of scanning a Cathode Ray Tube within a Chain Home station was done by women in the Women’s Auxiliary Air Force. It was their expertise that made Chain Home a success as the earlier they detected aircraft gathering over the Pay de Calais, the earlier Fighter Command could assess and act on the situation. As the stations were inviting targets for Luftwaffe attacks, the work by its very nature was very dangerous.