The Observer Corps was officially formed in 1925. A series of observation posts were established during the First World War to spot and identify enemy aircraft over Britain. The Observer Corps built on the legacy of this system.
The radar stations positioned along the coast were only able to look outwards. Once inland, it was up to the Observer Corps to identify enemy aircraft and to estimate the size and height of the formations. This information was passed to an Observer Corps Centre and then to Group and Sector Station Operations Rooms where it was used to inform Fighter Command's operations.
In 1941, in recognition of their contribution, the Observer Corps became the Royal Observer Corps (ROC).
The ROC continued to serve throughout the Second World War. They provided early warning of air raids and later in the war helped spot incoming V1 and V2 rockets. Observers even served aboard the invasion fleet on D-Day to give early identification of incoming aircraft.
The Observer Corps and the Battle of Britain
Learn more about the Observer Corps and hear from IWM curator Adrian Kerrison on how these expert aircraft spotters helped save Britain from invasion in 1940.
What's that? That? These? And this? Quick is it one of ours?
If you got this right as a member of the Observer Corps you may just have saved the lives of dozens of civilians.
The Battle of Britain was fought in the air. Heralded as 'the few', just under three thousand RAF aircrew faced Luftwaffe from July to October 1940.
Footage: "Never, in the field of human conflict was so much owed by so many to so few" -
However, throughout the battle, a secret army of 30,000 volunteers played a crucial role in their success. Standing day and night in hundreds of observer posts across Britain it was in fact a network of highly trained plane spotters that may just have swayed Britain into victory.
Footage: "From the southwest"
"Got'em, they're Junkers"
"four, southwest heading north east"
In the 1930s, it became increasingly clear that Germany's military was rapidly expanding and this was especially true of its air force the Luftwaffe.
Footage: "Here comes the Luftwaffe, in dozens of flights, hundreds of planes."
Britain was under no illusions that if war broke out with Germany the nation would be extremely vulnerable to air raids that would be much more devastating than those it had experienced in the First World War. Aircraft speeds increased so much in the interwar years that RAF fighters would not be able to intercept and prevent attacks unless they had early warning.
When Hugh Dowding was appointed the Chief of RAF Fighter Command in 1936, he immediately set about to solve this problem.
Adrian Kerrison: "So, in addition to the networking system set up by the Observer Corps in the 1920s and 30s, Dowding also added the new technology of radar as well as a system of command and control that allowed the RAF to rapidly communicate information through the chain of command.
One of the most important aspects of the Dowding System was that it allowed the RAF to know when and where to expect enemy raids. So, radar operators will be able to detect raids forming across the channel and also track them as they approach the coast. But the radar network had a very major limitation in that the radar masts only looked out to sea. So once the enemy aircraft crossed the coast, the radar network was effectively blind and this is where the Observer Corps came in."
When war broke out in 1939, the Observer Corps numbered some 30,000 volunteers and had around a thousand observer posts spread across Britain.
Adrian Kerrison: "So, during the Battle of Britain in 1940, the Observer Corps were made up almost entirely of volunteers, about 30,000 in number, and these volunteers were actually very highly trained and one of the most important things that they were trained in was aircraft recognition or determining whether the aircraft above them was friend or foe.
So, to learn aircraft recognition they'd use booklets, playing cards, posters, models even films that would help them identify aircraft silhouettes and at the same time they were also highly trained in tracking and reporting enemy aircraft, estimating altitudes and even detecting aircraft by sound using their ears."
Posts were spaced apart at intervals of six to ten miles and were organised into regional groups, with each group having an observer centre or headquarters where post information was received and processed.
Adrian Kerrison: "So, they basically reported the size of the raid, how many enemy aircraft there were, sort of like a general type, its estimated height and its direction, so where it was going. And then this would be processed in the observer centre, where it would be plotted on a large table map in an operations room and then this information will be looked at and sent directly to RAF fighter stations where they plot it on their own table maps in an operations room, and then the controller in the operations room would use that to basically scramble his fighters and send them to attack the enemy."
Ultimately, it was the Dowding System and the significant role that the Observer Corps played in it that gave the RAF the vital edge they needed to achieve victory over the Luftwaffe in the Battle of Britain.
Adrian Kerrison: "At the moment the German aircraft crossed the coast, without the Observer Corps there would have been absolutely no way to track them, there would have been no way for RAF fighter controllers to tell their aircraft where to go, so without them, it would have more or less made the radar useless because enemy aircraft could have changed direction, they could have changed height - so this was why the Observer Core was so important."
In 1941 the Observer Corps was granted the Royal prefix by King George VI in recognition of its important contributions during the Battle of Britain and thereafter. It continued to play a significant role in the war including during the D-Day landings.
The observer posts and centres were manned continuously until the 12th May 1945, four days after VE Day.
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