Many things helped the Allies win World War II, 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 of the story. 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 World War I. 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. With numerous maps and structural studies, the book 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.