In the early days the "Corps" was made up of special constables and constables who voluntarily gave up their spare time to go "aeroplane watching." It was soon realised that all responsibility was passed on to them after enemy aircraft had crossed the coast so more and more people were drafted into the 'Corps' and it became a military establishment controlled by Fighter Command.

The Observer Corps had over 32,000 men who manned about 1,400 command posts scattered all around the coastal areas of Britain. The southern and south-eastern coast around Hampshire, Sussex, Kent and Essex had the most command posts.

The main duties of Observer Corps members were to observe, locate and estimate enemy aircraft strength, height and direction. But other important duties were to report the location of crashed aircraft of both the RAF and the Luftwaffe. They also had to watch out for pilots that had parachuted to safety and accurately establish their location, especially if they happen to be out over the sea. This speeded up the process of the RAF Air-Sea Rescue or Coastal Command reaching pilots before they either suffered from the effects of being in the water or before they drowned.

The men of the Royal (this prefix was given in 1941) Observer Corps made a valuable contribution to the Battle of Britain. Without them Fighter Command would have been 'blind' once enemy aircraft formations had crossed the coast.