During World War 2, military wireless intercept facilities were everywhere. Long-range monitored theaters of operation. Short-range units dug in with the troops. 

Britain and Commonwealth nations called their long range facilities the “Y Services“. Americans had the Signals Intelligence Service, later the Signals Security Agency. For Germany, it was “intercept service”.  For Japan, simply radio intelligence, which mostly focused on U.S. Navy traffic analysis. The Soviets were initially not much interested in wireless intercept. Instead, they preferred using agents and stolen documents. But they caught on.

Y Stations dotted the English countryside. Ground, sea and air transmissions poured in from Europe, Africa and the Atlantic.This was an era of highly directive rhombic antennas that stretched for miles. Technicians learned how to attach multiple receivers to these antennas. Some stations listened through time delays so they could choose what to record. Special teletype circuits were set up to share information with monthly volumes of between 200,000 to 400,000 interceptions.

Both sides used similar interception and direction finding technologies throughout the war. Advantages ebbed and flowed. Far flung listening posts in the United States, India and Oceania provided some additional benefits over German listening posts mostly clustered in Europe. In Canada, the Navy simply took over existing government monitoring stations. Listening posts set up in New Zealand and Australia were able to monitor at great distances across the oceans. The Americans had large facilities in Virginia, California and Hawaii.

Listeners either monitored assigned frequencies, or did search-and-pounce across various bands. Radios remained powered-up for the duration of the war, unless they broke down.

Some stations focused more on direction finding. These required proper spacing to support triangulation. Most used the Adcock HF/DF technology.

Military Wireless Intercept Facilities at the Front

As war progressed, fixed stations were complimented by thousands of mobile, portable listening points in combat zones. Some were on warships, and a few aboard aircraft. Radio intercept became essential for military tactics. Typically, both sides were able to discern enemy order of battle from traffic analysis alone. Y intelligence was critical for air maneuvers, i.e. developing systems of fighter escort which enabled longer and more effective periods of engagement.

German Navy B-Dienst service was quite successful in pinpointing convoy locations. In the Pacific, army radio personnel set up temporary listening points on many islands. During offensive operations, the listeners moved with the troops. Near the front lines, many low-priority messages used plain text and were a source of immediate intelligence.

In addition to listening to the enemy, SIGINT units monitored their own forces looking for poor radio discipline and lapses in security. The Allies also monitored each other to ensure they knew what was happening nearby. Maintaining friendly radio discipline was very important during troop build up in England prior to D-Day.

Discipline came from culture and lessons learned. The British were the most disciplined but even they had failures that made a difference, particularly in North Africa which provided for many of Rommel’s early success. However, after the first battle of El Alamein, the British captured a large German Y service unit almost intact. They were amazed at how successful the Germans were at SIGINT and this changed their procedures going forwards. The most effective discipline, though, was simply radio silence.