While doing a little research for the radio-amateurs-in-Ethiopia book, I was blindsided by my next two books:

Sir Francis Walsingham ran a postal interception bureau with some cryptanalytic capability during the reign of Elizabeth I, but the technology was only slightly less advanced than men with shotguns, during World War I, who jammed pigeon post communications and intercepted the messages carried.
—http://en.wikipedia.org/wiki/SIGINT_in_Modern_History

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