BBC recently put out a fantastic article about one of UK's many volunteer wireless interceptors.
During World War II, dozens were recruited by MI8 - a division of the British Military Intelligence department, and a cover name for the now-defunct Radio Security Service (RSS).
The purpose of their work was to intercept secret wireless transmissions by German and Italian agents in Britain.
This kind of intel was extremely important in the war to figure out what the enemy knows and thinks. Incidentally that is also one of the cornerstones of a good strategy game so who knows, maybe Mr King's legacy will also be featured in Spymaster!