In 1939 Germany invaded Poland which marked the start of World War II. Less than a year later most of Western Europe was under Nazi control. Hitler now turned his attention to Great Britain. In order for an invasion to succeed, Hitler needed control of the English Channel. Hitler's Navy was not up to the task so he relied on the Luftwaffe which, up to now, had smashed all resistance. On paper the Luftwaffe looked the superior force with 2,400 fighters and bombers up against 900 British fighter planes. Facing such overwhelming odds the British needed a way to eliminate the German element of surprise and target the incoming forces.

Hope was restored with the development of the Chain Home radar system. This system was possible through the extraordinary work of a radio researcher named Sir Robert Watson-Watt. By 1940 the British had in place an entire network of long-range early warning radar stations that were tightly integrated by Fighter Command. This system could detect planes at a range of 150 km. Radar was an exceptional force multiplier as it allowed the British to concentrate their limited resources in areas where they were needed. British fighters were no longer needed to fly constant missions over the East Coast of England and less time was spent in the air patrolling the sky.

German radar operated in a narrow frequency range and was susceptible to jamming. Early attempts to disrupt enemy radar came in the form of chaff. Chaff was made from aluminium strips cut to exactly a quarter of the length of the radar's wavelength. Chaff was first used in July 1943, when Hamburg was pounded by a relentless bombing raid. The chaff reflected the German radar which cluttered the screens of Air Defence. With German air defence completely blinded, allied bombers were free to bombard the city without fear of attack from enemy fighters.

As the war unfolded, higher and higher frequencies were been used. The Chain Home radar system used frequencies of around 20 MHz during the war. By the end of the war, invention of the magnetron enabled the American H2S bombing radar to operate at 3GHz. Such a high frequency gave an excellent resolution of the underlying terrain.,

By the end of the Battle of Britain over 1,400 German Aircraft were destroyed with the loss of many trained pilots as opposed to 900 British fighters with the loss of half the British pilots.