As the long, hot summer ran into October, the German daylight bomber losses became too heavy. Their bomber force started to operate only at night, and the damage they caused to Britain's cities was enormous. Many civilian organisations were set up to help deal with the wounded people and damaged buildings.
The German raids continued, but the RAF had started to develop night fighters equipped with radar which could tackle the problem. The first AI (Airborne Intercept) radar sets were being fitted to Blenheim, Defiant and Beaufighter aircraft, and proved increasingly effective as the equipment developed and operational experience increased.
During the day, German fighters, mostly Me 109s but occasionally Me 110s, were sent over carrying bombs in small and large scale Jagd-bomber or "Jabo" raids. Largely these nuisance raiders were aimed at engaging the RAF fighters and disrupting defensive operations over the South-East. Defenders, tired from the night attacks, were stretched still further by these raids. They flew fast and high and were difficult to intercept. The radar warning was not long enough to allow a Spitfire to climb to this height from the ground, so the RAF had regular patrols between 15,000 and 20,000 feet. This was a costly and inefficient use of the aircraft and pilots, exactly the situation the control system had helped to avoid during the earlier phases of the Battle, but German losses began to increase. The weather also began to worsen and the raids stopped in late October.
The Germans then realised that the RAF could not be defeated in 1940. Germany was also preparing to attack Russia, so Operation Sea-Lion was cancelled indeffinitely and eventually abandoned altogether. The Battle of Britain was over. Strangely, for such a ground breaking Battle, the first to be decided purely in the air and the first real test of air power as a defensive and offensive weapon, it did not really end, so much as petered out