The US Marines used a code Japan's cryptographers never cracked — spoken Navajo

The US Marine Corps recruited Navajo speakers to encode radio messages in the Pacific during WWII, using a language that had no written form and was spoken almost nowhere outside Navajo communities. Japanese codebreakers never broke it, and a Marine signal officer credited the code talkers as essential to taking Iwo Jima.

— Chester Nez, Code Talker: The First and Only Memoir By One of the Original Navajo Code Talkers of WWII — 2011
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