Since the end of the First World War Secret bases were created to hide ammounts of supplies, but it was at the begining of the Second World War that vast bases were built. This book is an complete study of all such sites from the central ammunition depot at Corsham which extended over 200 acres underground holding over 350,000 tons of ammunition even complete aircraft engine factories were built underground safe from bombing. Even the countries Art treasures were moved from London to Wales to central Art Repositories for safe keeping the entrances then concealed. The book even continues into the Cold War period.