The development of radar in Britain was key in 1939 to detecting anything coming across the channel. This was key to interception.

 

The development of radar in Britain was key in 1939 to detecting anything coming across the channel. This was key to interception.

Absolutely, but knowing when and where the attack is coming from doesn't do you any good if you don't have any airfields for the aircraft responsible for doing the interception to take off from. The fighters' primary responsibility was to attack the bombers, but often when they did that and tried to return to their base, they couldn't land because other bombers had rendered the fields inoperable in the meantime. The RAF's infrastructure was being degraded at an unsustainable rate, even in the short term, until Germany turned its attention from the airfields to the cities. That allowed the RAF to recover and even expand its operations to the point that losses for the Germans were unsustainable.