Signals Intelligence, or SIGINT, is the interception and evaluation of coded enemy messages. From Enigma to Ultra, Purple to Lorenz, Room 40 to Bletchley, SIGINT has been instrumental in both victory and defeat during the First and Second World War. In the First World War, a vast network of signals rapidly expanded across the globe, spawning a new breed of spies and intelligence operatives to code, de-code and analyse thousands of messages. As a result, signallers and cryptographers in the Admiralty's famous Room 40 paved the way for the code breakers of Bletchley Park in the Second World War. In the ensuing war years the world battled against a web of signals intelligence that gave birth to Enigma and Ultra, and saw agents from Britain, France, Germany, Russia, America and Japan race to outwit each other through infinitely complex codes. For the first time, Peter Matthews reveals the secret history of global signals intelligence during the world wars through original interviews with German interceptors, British code breakers, and US and Russian cryptographers. "SIGINT is a fascinating account of what Allied investigators learned postwar about the Nazi equivalent of Bletchley Park. Turns out, 60,000 crptographers, analysts and linguists achieved considerable success in solving intercepted traffic, and even broke the Swiss Enigma! Based on recently declassifed NSA document, this is a great contribution to the literature." - The St Ermin's Hotel Intelligence Book of the Year Award 2014