Read this: Nevertheless, it was radar that proved to be critical weapon in the night battles over Britain from this point onward. Dowding had introduced the concept of airborne radar and encouraged its usage. Eventually it would become a success. On the night of 22/23 July 1940, Flying Officer Cyril Ashfield (pilot), Pilot Officer Geoffrey Morris (Observer) and Flight Sergeant Reginald Leyland (Air Intercept radar operator) of the Fighter Interception Unit became the first pilot and crew to intercept and destroy an enemy aircraft using onboard radar to guide them to a visual interception, when their AI night fighter brought down a Do 17 off Sussex. On 19 November 1940 the famous RAF night fighter ace John Cunningham shot down a Ju 88 bomber using airborne radar, just as Dowding had predicted.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What was critical in the night battles over Britain?
radar