The Royal Observer Corps was established in 1925. By the 1940s, a secret army of volunteers were tracking all the incoming raids during the Second World War. Tens of thousands ensured that a network of observation posts were continuously manned.

When the Second World War broke out, there were 30,000 observers working at 1,000 observation posts, which were manned continuously. They were volunteers, who trained themselves in aircraft recognition and how to estimate an aircraft's height.

During 1940 and 1941 radar technology was developed, and soon a chain of coastal radar stations plotted raids. However, they couldn’t track aircraft inland and manual tracking was needed. The Observer Corps stepped up.

Their information was sent first to an Observer Corps Centre, and then on to Group and Sector Station Operations Rooms – like the one at IWM Duxford. The system worked well in good weather but the observers struggled in rain or low cloud.

Photographs and films in our collections suggest that the Royal Observer Corps were not as publicly celebrated as the pilots. But pilots themselves did not take these hardworking volunteers for granted.

They were hugely appreciated for helping home crippled or lost aircraft, as well as spotting and plotting the movements of enemy machines, coming to engage in battle.

Observer Corps had ‘forewarned is forearmed’ written across their caps and badges. Their careful watch of the skies was one of the starting points of crucial ‘on the ground’ information used to plot airborne skirmishes in real-time.

Every single aircraft they saw was plotted. This even included training aircraft, and groups of returning RAF squadrons.

Members of the Observer Corps identified every type of aircraft they saw, estimated their speed and height, and worked in close liaison with the RAF in transmitting air raid warnings.

One photograph boasts that, at a particular Observer Post in the country, the personnel represented a full cross-section of the community. Their team included an accountant, mechanic, stockbroker, solicitor's clerk, stoker, patent agent, company secretary, commercial traveller and farmer. Both men and women volunteered for service.