An Observer Corps spotter scans the skies of London.

MMM

The Observer Corps provided vital information about incoming German Luftwaffe raids. A chain of coastal radar stations was used to plot the raids but, in 1940, they were unable to track aircraft inland and manual tracking was needed which meant people watching the skies through binoculars!

MMM

The Observer Corps was largely made up of volunteers, who mostly trained themselves in aircraft recognition and how to estimate their height. When the war broke out, there were 30,000 observers and 1,000 observation posts, which were manned continuously. Their information was sent first to an Observer Corps Centre, and then on to Group and Sector Station Operations Rooms. The system worked well in good weather but the observers struggled in rain or low cloud.

MM

Source: Wikipedia/IWM