In this episode of Warfare we hear about what was happening behind the closed doors of GCHQ during the 20th century, from somebody who has been given access to the files (a lot of them anyway!). Hear John Ferris, the authorised historian of GCHQ, and professor of History at the University of Calgary as he takes us through what he has learnt about the relationships between the governments and organisations of the world, and the secrets they have kept. Through his studies of signals intelligence (SIGINT) John takes us all the way back to the First World War to discuss whether it really ended in 1918, and right up to the Snowden scandal and changes that have emerged with cyber terrorism.