In 1935 Robert Watson-Watt wrote a paper entitled The Detection of Aircraft by Radio Methods. This was presented to Henry Tizard, the chairman of the Committee for the Scientific Survey of Air Defence. Tizard was impressed with the idea and on 26th February 1935, Watson-Watt demonstrated his ideas at Daventry. As a result he was appointed head of the Bawdsey Research Station in Felixstowe.
Watson-Watt's was based on the idea of bouncing a radio wave against an object and measuring its travel to provide targeting information. It was called radar (radio detection and ranging).
By the outbreak of the Second World War in September 1939, Watson-Watt had designed and installed a chain of radar stations along the East and South coast of England. During the Battle of Britain these stations were able to detect enemy aircraft at any time of day and in any weather conditions.
Radar was also used by ships and aircraft during the war. Germany was using radar by 1940 but Japan never used it effectively. The United States had a good radar system and it was able to predict the attack on Pearl Harbor an hour before it happened.
Britain tended to have the best radar system during the early stages of the war and in 1940 the invention of the Magnetron cavity resonator enabled more centimetric waves to be transmitted. It also enabled more compact high-frequency sets to be used by aircraft in the Royal Air Force.
In 1941 the Royal Navy began employing the ASV-3 radar system that helped them locate and attack U-Boats. In December 1942, the RAF began using the Oboe navigational system. A control station in Britain broadcast a radar beam in the direction of the target, and another beam tracked an Oboe-equipped Pathfinder bomber. A person in the control station could then guide the aircraft directly to the target.
The plans for the air defence of Great Britain had as early as the autumn of 1937 been rewritten round the assumption that the promises made by our scientists for the still unproven Radar would be kept. The first five stations of the coastal Radar chain, the five guarding the Thames estuary, had watched Mr. Chamberlain's aeroplane go and come on its peace missions of September 1938. Eighteen stations from Dundee to Portsmouth began in the spring of 1939 a twenty-four-hour watch, not to be interrupted in the next six years. These stations were the watchdogs of the air-raid warning service; they spared us alike grave losses in war production and intolerable burdens on our Civil Defence workers. They spared the anti-aircraft gun crews needless and tiring hours at action stations.
They saved us from the exhaustion of man and machine that would have doomed our matchless but slender fighter force had it been compelled to maintain standing patrols. They could not give the accuracy required for night-time interception, but they enabled the day fighters to await their prey at the most favourable altitudes and aspects for attack. In their decisive contribution to victory in the day battles they were supported and supplemented by other stations of new technical design, which gave warning - all too brief, but invaluable - of the approach of the low fliers.