During the Second World War German intelligence had deployed wireless teams throughout occupied Europe. Agents had even been deployed to mainland Britain to spy on British military activity. Monitoring and reporting of their wireless transmissions fell to a small, secretive and largely unknown unit manned almost exclusively by volunteers. The Voluntary Interceptors (VI) as they became known would spend hours every day at home monitoring the short wavelengths for often faint and difficult to copy signals transmitted by these German secret intelligence services. This unit was to become known as the Radio Security Service (RSS) and was at the core of the signals intelligence production effort at Bletchley and the insights into German military tactical and strategic planning. Without interceptors like the RSS, Bletchley would not have existed. Their story has never truly been written and Radio War focuses on the secret world of wireless espionage and includes first-hand accounts from the surviving veterans of the unit. Its existence was only made public 35 years after WWII ended, shortly after Bletchley Park’s secrets were exposed. Patrick Reilly, the Assistant to Head of MI6 Stewart Menzies, was to say of the RSS.… ‘a team of brilliance unparalleled anywhere in the intelligence machine.’