For much of the twentieth century, the Royal Observer Corps served an important role in monitoring the skies above Great Britain and providing warning of potential enemy air attacks against cities, industry and military installations alike. Skywatch provides a history of the ROC from its establishment in 1925 through to its stand down in the 1990s with the end of the Cold War. Volume 1 of Skywatch examines the early years of this organisation up to the outbreak of the Second World War in 1939.

During the First World War, London was vulnerable to air attacks by Zeppelins and later, German bombers. To defend the capital, the London Air Defence Area was created to coordinate the efforts to protect it. However, after 1918, the system was quickly abandoned.

In the early 1920s, the Committee for Imperial Defence began to reconsider the problem. In 1924, the first experiment was conducted to monitor and report the movement of aircraft overland by using small groups of aircraft observers reporting to a central point. This successful experiment led to the creation of the Observer Corps in 1925 under the control of Police Chief Constables.

Originally intended to cover just the South East of England to protect London, as the threat from resurgent Nazi Germany grew, the Corps was gradually expanded to cover nearly the whole of Great Britain by the start of the war. Now transferred to the control of the Air Ministry, Observer Corps Groups became a key part of Fighter Command’s integrated air defence system, unique in that it was the only means to track the movement of aircraft once they crossed the coast and headed inland.