Signals intelligence is one of the most secretive areas of government, and prior to this study very little information on post-war intelligence gathering has entered into the public domain. The ruined buildings of the Teufelsberg offered a rare if not unique opportunity to study the architecture of a relatively modern intelligence-gathering centre, one developed to house vast banks of data processing machines. The Teufelsberg was one of the West’s most important listening stations. Its location and presence was impossible to hide. Instead the operational buildings hid in plain sight behind plain facades finished in a neutral blue and white colour scheme. The specialist monitoring apparatus used by the British was a mixture of military and civilian equipment. Across the four decades from 1950, communications technology evolved from glass valve and transistor electronic circuits, supported by electro-mechanical systems, to the forerunners of modern digital systems.