The Radio Security Service was a WWII secret organisation, the existence of which was not revealed until 1979 (several years later than Ultra and Bletchley Park). These pages explain how several thousand Morse Code readers, mainly licensed radio amateurs, penetrated the enemy secret services and had as a result a profound influence on various military operations, especially the Normandy landings and beyond. A total of 268,000 coded messages, picked up by these amateurs, were decoded at Bletchley Park.

Read about how some 1,500 Voluntary Interceptors eavesdropped on the various enemy secret transmissions by listening to short wave radio signals in complete secrecy yet in their own homes. As time passed, full-time monitoring took place in several purpose-built stations using the best possible equipment and aerials. Without these skilled operators, the control of German spies in this country would not have been possible.

The early days of the Voluntary Interceptors can be found here

https://cdmnet.org/RSS/SecretListeners/index.html

https://cdmnet.org/RSS/SecretListeners/  

The Voluntary Interceptors were eventually coordinated  in a large house near Barnet called “Arkley View”
Many of the volunteers became involved in Direction Finding
Initially the Voluntary Interceptors were looking for spies but later helped with counter-espionage
Many of the participants only found out their role in 1979 when Renee Cutforth’s documentary researched by Paul Cort-Wright (G3SEM) appeared on BBCTV. See a copy here:   http://eafa.org.uk/catalogue/5108