It was a German physicist Heinrich Hertz who in 1887 began experimenting with radio waves in his laboratory. He discovered they could transmit through certain materials but was affected by others. In 1904 another German Christian Hulsmeyer gave public demonstrations of his patented Telemobiloskop which used radio echoes to detect shipping to avoid collisions at sea.

In Britain and the USA physicists continued the work, but the invention was all but ignored for 30 years in Germany until in 1934 two German scientists Hans Hollmann and Hans-Karl von Willisen built the first commercial version of radar for use by shipping. The Kriegsmarine showed enormous interest and in 1935 pulse radar was invented. Eventually the Luftwaffe became interested ordering a dozen sets of what later became known as Freya

German radar had almost nothing in common with British radar as the Germans used a wavelength one tenth that of the British home chain stations. Although having lower range the system had better resolution. The Telefunken Company developed an improved version of radar that became known as Wurzburg, mainly for home defence. Radar although of immense value to the British during the Battle of Britain, was only utilised by the Germans in a limited role for tracking shipping in the Channel.

British radar came about because of a far fetched idea at the end of 1934 at the Aeronautical Research Committee under the leadership of Robert Watson-Watt (1892-1973) a radio expert he was asked about so called rumours rife at the time about a German "death ray" a magnetic weapon that it was suggested could shut down aircraft engines.

Watson-Watt dismissed this fanciful rumour and like aircraft designers Sidney Camm and Reginald Mitchell he would make key behind the scenes technical contributions to the success of Fighter Command. Watson-Watt a descendent of the 18th Century inventor James Watt, experimented with equipment that could detect long range radio signals given off by thunderstorms and discovered that these radio waves were "bounced back" to earth not only by certain weather conditions but also by the metal fuselages of the aircraft overhead.

12th February 1935 Watson-Watt and his team produced a crucial report "The Detection and Location of Aircraft by Radio Methods" that impressed the Air ministry and of particular note Sir Hugh Dowding soon to become CO of Fighter Command. Watson-Watt demonstrated his theory by having a Handley Page Heyford bomber fly along the centre line of a 150 foot radio beam transmitted by the BBC station at Daventry, the detection equipment using a cathode ray oscilloscope showed a significant "disturbance" of the signal when it picked up the aircraft eight miles distant.

An experimental unit was set up and further funding granted so that by the end of 1935 the range had extended to 50 miles and plans were drawn up to create 20 coastal "home chain" stations. By the end of 1936 the range had extended to 100 miles. By the summer of 1940, 32 stations had been established. The one drawback was that these transmitters could not detect low flying aircraft, so to fill the gap mobile units were established using a lower frequency.