Many things helped the Allies win the Second World War, but none was more important than radar. Radar’s decisive role in 1940 is widely known – the tall towers of the Chain Home stations stand beside the hurricanes and Spitfires, beside Churchill, Dowding and the men and women of Fighter Command as enduring symbols of Britain’s ‘finest hour’. Yet the Battle of Britain was just one episode in the story of British radar. Already by 1940 the system had a long history: five years in the building, the Chain Home layout was shaped by strategic thinking extending back to the First World War. Victory in 1940 secured radar’s future in every domestic campaign over the next five years. By 1941 radar stations were controlling night fighters in the Blitz. A year later they were scanning the sea approaches, sentinels against Hitler’s navy and invasion fleets. By 1943 radar was preparing to meet the V-weapons – a threat barely conceived when research began, just eight years before. Diversity fostered growth. Many more radar stations were commissioned in the five years after 1940 than in the same period before. Radar was many things: a triumph of applied science, certainly and a strategic miracle, too; but it was also a pattern of places – a growing network of sites and stations, large and small, temporary and permanent. Building Radar is the first attempt to reconstruct the growth of that network in detail. With numerous maps and structural studies, it presents the history of British ground radar through its fabric and evolving geography, showing how the system was shaped by the march of war and as it grew, provided a new focus for the talents of engineers, designers and builders. As the third volume in the English Heritage series Monuments of War, Building Radar also assesses the survival of wartime radar stations in today’s landscape, showing how protection of these remains is being assured by statutory means.