The Navajo Code Talkers' Unbroken Code

Navajo code talkers developed a battle code based on their language that was never broken by enemy forces. Unlike machine-encrypted codes (like the German Enigma which WAS broken), the Navajo code was based on an unwritten language with only about 30 non-Navajo people in the world who spoke it fluently — and none were Japanese. Japanese intelligence captured a Navajo soldier (who was not a code talker) and forced him to listen to radio transmissions for hours, but he couldn't make sense of it. Philip Johnston, the son of a missionary to the Navajo Nation, proposed the idea to the Marines. The last code talker, Chester Nez, died in 2014 at age 93.