Because it gave them early warning when the Luftwaffe or German air force were about to attack somewhere across the English Chanel . the RAF had time to challenge them & down them before they got to there destination.
Radar
Are you perhaps asking about chaff, used to jam enemy radar?
Yes, radar helped to pick up German aircraft after about 1940.
The RAF never bombed England - they were fighting FOR Britain.
Radar enabled the RAF fighters to get airborne before they were could be bombed and the ground - and to confront the enemy in the sky.
RADAR was invented in England. That gave them an advatage in the air and on the coast. Eventually Germany had it but their radar system was not as good.
Royal Radar Establishment was created in 1953.
Technology that helped Britain's Royal Air Force combat the German luftwaffe starting in the Battle of Britain
The first one was a Radar, it gave them an advantage on the number, speed, and direction of incoming airplanes and the second was a German code-making device that enabled the British to decode many German codes.
The Royal Artillery is responsible for the firepower of the British Army and copious regiments across the United Kingdom and a few in the North-Western region of Germany. According to the British Army website, the Royal Artillery supplies the British Army with radars.
Royal Radar Establishment Automatic Computer was created in 1962.
The Royal Air Force, Spitfires and Hurricanes, and Radar. Radar spotted the German airplanes coming and the Spitfires and Hurricanes shot them down. If it were not for Radar, Spitfires and Hurricanes, the Germans would have tried to invade England. Thank goodness for Radar, Spitfires, Hurricanes and Prime Minister Winston Churchill.