Starting in 1940, Germany was subjected to a growing threat of Allied bomber attack. The RAF night bombing offensive built up in a slow but unrelenting crescendo through the Ruhr campaign in the summer of 1944 and culminating in the attacks on Berlin in the autumn and early winter of 1943-44. They were joined by US daylight raids which first began to have a serious impact on German industry in the autumn of 1943. This book focuses on the land-based infrastructure of Germany’s defense against the air onslaught. Besides active defense against air attack, Germany also invested heavily in passive defense such as air raid shelters. While much of this defense was conventional such as underground shelters and the dual use of subways and other structures, Germany faced some unique dilemmas in protecting cities against night fire bomb raids. As a result, German architects designed massive above-ground defense shelters which were amongst the most massive defensive structures built in World War II.