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Sigsaly, or the Green Hornet, was a communications device using spread spectrum and a form of PCM for ultra secret communication during the war. The "key" was contained on a 78 rev/min record which was physically broken after use.

There were several misleading stories written about it at the time to confuse the enemy, and they have also survived to confuse modern historians.

One such story said that the records mixed noise with the transmissions. Playing a similar record at the other end produced a signal that could be subtracted to leave the original speech. (Just try doing it with 1940s equipment!)

More about the technicalities of this system can be found on

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