During the 1970s, the United States conducted a daring Signals Intelligence (SIGINT) operation against the Soviet Union called Operation Ivy Bells in the Sea of Okhotsk. Whereas any other message with a reasonable expectation of intercept would have been encrypted, some key communications under the Sea of Okhotsk took place in plaintext. Using a device that captured signals moving through the cable via electromagnetic induction, United States intelligence was able to retrieve sensitive military communication from hundreds of feet below the surface of the sea. It was a powerful demonstration of sniffing—the capture and analysis of data moving through a communications channel.
Decades earlier, the Allies were preparing to liberate Nazi-occupied Western Europe in the 1944 Battle of Normandy. A critical component of success was catching the Germans...
