One of the most important contributory factors to the success of the air defences during the Battle of Britain was the early warning system known as Radio Direction Finding or Radar.

In the 1930s, when the development of a new generation of fast monoplane fighter aircraft promised the possibility of defence against air attack, it was realised that improvements in early warning techniques would be equally as necessary. As Britain was so close to the continent, some method was required to warn the defences as quickly as possible of the approach of hostile raiders. Constant aircraft patrols were too expensive to deploy.

The science of the detection and location of aircraft by radio beams made such rapid progress from the first experiments in February 1935 that exactly five years later a chain of coastal radar stations covering the east and south sides of the country was operational. At 10,000 feet, intruders could be detected at ranges of 50-120 miles. As ranges for low-flying aircraft were much shorter, a string of Chain Home Low stations to detect aircraft flying at 1,000 feet and below was built after the war began.

The Germans made a concerted attack on radar stations in Kent, Sussex and the Isle of Wight on 12 August and a few, unco-ordinated raids thereafter. Only Ventnor was put out of action for any significant period. Apart from the difficulty in destroying the open, lattice work structures of the transmitting and receiving masts, the Germans never fully understood the crucial role of radar to the British and, therefore, did not place the highest of priorities on its destruction.

Radar was the eyes of Fighter Command, without which it would have been unable to see incoming raids early enough to have directed defending fighters to intercept. But its effectiveness was greatly enhanced by being only one element of, and integrated into, a sophisticated command and control network which received the raw information of radar plots and rapidly applied it to direct the use of precious resources of pilots and aircraft to the best possible effect.