For hundreds of years Britain has been portrayed as an island fortress, impregnable since 1066, a self-sufficient nation protected by the sea around it. By exploring the fortresses and defensive structures of coastal Britain, Dan Cruickshank in the BBC series Invasion seeks to dispel this popular myth and provide an argument that Britain is a nation whose history is instead defined by the fear of invasion. This book analyzes the science of warfare and the military heritage of the country in its medieval castles, coastal tunnels, gun emplacements, World War II deep bomb shelters and more. It reveals fortresses both brilliant and hopeless.