Recent display of Airpass AI23 Radar unit (1955) kindly loaned by Selex Galileo
The outcome of this appointment was Watson-Watt's proposal that a chain of radio direction finding (RDF) or 'chain home' (CH) stations be built around the British coast. By the time war was declared, there were 18 operational Chain Home stations round the south and east coast of England, capable of detecting enemy aircraft 100 miles away. By 1944, there were 208 stations ringing the entire UK coast, forming a highly efficient early warning system. The Chain Home system successfully detected the approach of enemy aircraft, enabling the Royal Air Force to deploy its resources effectively, which resulted in victory in the Battle of Britain.
The English Electric Lightning, a supersonic fighter aircraft developed in the early 1950s, required high-quality Radar to fulfil its role as an Interceptor. The Radar work was contracted to Ferranti Ltd in Edinburgh, to a plant that had been established during the war to manufacture gyro-stabilised gun-sights and therefore knew something about fire-control. The Ferranti engineers used a great deal of innovation to produce the Airpass family of fire-control radars, achieving a new level of sophistication at a low weight level.
The Lightning radar, designated A.I. 23, performed fire-control computation for the Red-Top Infra-Red missile and for Air-to-Air gunnery. Detection range was typically 40 miles against the Russian 'Bear' bomber which was a primary target over the North Sea during many cold-war interceptions. The radar would guide the Interceptor to close range, often at night, where a floodlit tail photograph could be taken and a token diplomatic protest lodged. Later developments of the Airpass series radars included ground-mapping and air-to- surface depressed-sightline weapon delivery.