The Radio Security Service (RSS) was established in September 1939, following an investigation and report by Lord Hankey, with the responsibility for detection of illicit wireless communications within the UK and surrounding sea. Initially under the control of MI8 of the War Office, and using physical facilities provided by the Post Office, RSS supplied the Security Service with details of intercepted communications.
In May of 1940 RSS was made responsible for interception of German overseas illicit transmissions, and by the end of 1940 for the global interception of enemy secret service communications. In January 1941 RSS passed to the control of the Secret Intelligence Service (SIS), and in August of that year it assumed responsibility for the overseas interception units, previously under MI8 control. As well as targeting known enemy radio-communications networks, RSS undertook systematic searches and analysis of the radio spectrum looking for illicit broadcasts, which could then be targeted. These searches utilised home-based volunteer interceptors, who reported their findings by post to RSS.
At RSS headquarters in Barnet, the Radio Intelligence Section of RSS undertook intelligence analysis in co-operation with the Government Code and Cypher School (GC&CS) and the SIS, which resulted in regular Radio Security Intelligence conferences. RSS also had responsibility for monitoring allied non-military communications, mainly within the UK. In 1946, RSS was taken over by Government Communications Headquarters (formerly GC&CS).
Source: Government Code and Cypher School: Administration Files on the Radio Security Service. Ref. HW34