THE RADIO SPIES AND THE WAR OF THE WIRELESS - WWII

Hidden away in lowly lit rooms, wearing headphones and with heads bowed, the radio spies silently worked. At the same time, the people of the Home Front unaware of this clandestine activity were also tuning in to their wireless sets. Motivated by inspiring and patriotic speeches from their wartime leaders they were busy with war work and defending the Home Front.

The radio interceptors were chosen for their agile minds, ability to work at speed, and also for the stamina required to work exhaustingly long shifts. At home and abroad the radio spies listened to the German transmissions, writing down morse code.

These coded transmissions, sent by the Germans, encrypted by Enigma machines, and received by the listening stations were sent to Bletchley Park. Once decoded they gave valuable information about bombing targets and invasion plans. Some Y stations, or Wireless Intercept stations, using direction finding, identified the position of German U boats. Voluntary Interceptors were also used. Radio hams, often with their own receivers, were secretly working from their own homes, and no one knew, not even their families! The work of the Y stations and Voluntary Interceptors was kept top secret.

In France, British planes dropped secret agents and spy suitcase radios to assist the work of the French Resistance.  Messages or instructions were relayed to the Resistance via news broadcasts.

In 1980, the truth about the work of Bletchley Park was revealed, although the contribution made by the radio interceptors is still to be fully acknowledged. Churchill's network or web of radio spies helped to shorten the war and save thousands of lives.

Source
Manpower - Ministry of Information -  published 1944 Alabaster Passmore and Sons, Ltd.
The Secret Life of Bletchley Park Sinclair McKay
The Secret Listeners Sinclair McKay