With few exceptions, amateur radio is a notably sedentary pursuit. Yes, some hams will set up in a national or state park for a “Parks on the Air” activation, and particularly energetic operators may climb a mountain for “Summits on the Air,” but most hams spend a lot of time firmly planted in a comfortable chair, spinning the dials in search of distant signals or familiar callsigns to add to their logbook.

There’s another exception to the band-surfing tendencies of hams: fox hunting. Generally undertaken at a field day event, fox hunts pit hams against each other in a search for a small hidden transmitter, using directional antennas and portable receivers to zero in on often faint signals. It’s all in good fun, but fox hunts serve a more serious purpose: they train hams in the finer points of radio direction finding, a skill that can be used to track down everything from manmade noise sources to unlicensed operators. Or, as was done in the 1940s, to ferret out foreign agents using shortwave radio to transmit intelligence overseas.

That was the primary mission of the Radio Intelligence Division, a rapidly assembled organization tasked with protecting the United States by monitoring the airwaves and searching for spies. The RID proved to be remarkably effective during the war years, in part because it drew heavily from the amateur radio community to populate its many field stations, but also because it brought an engineering mindset to the problem of finding needles in a radio haystack.

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