The U.S. deployed Cherokee and Choctaw Indians as code talkers during WWI. During WWII, other Native Americans, including Lakota, Meskwaki, and Comanche and Basque speakers, were also used.
A team of German anthropologists tried to learn Native American languages before the war, but the task proved too difficult. Nevertheless, aware of the German effort, the U.S. Army did not implement a large-scale code talker program in the European Theater of WWII.
In the Pacific Theater, however, Navajo code talkers were used extensively. Even among its closest Southwest relatives, the dialects and complex grammar of the unwritten Navajo language makes it virtually undecipherable to anyone without extensive exposure and training.
To conserve time, some military terms and concepts were given uniquely descriptive names in Navajo (e.g., “shark” referred to a destroyer). Code talkers memorized terms in a codebook that was never taken into the field (uninitiated Navajo speakers were unable to comprehend these messages).
Navajo code talkers continued to be deployed through the Korean and Vietnam Wars. Navajo code talking remains the only spoken military code that has never been deciphered.