In 1982, U. S. President Ronald Reagan named August 14 Navajo Code Talkers Day in honor of those Navajo men who passed coded communications throughout World War II, primarily in the Pacific theater.
Specially trained marines used their native language, known by very few outside their tribe, and created a code within that language. Other codes by other Native American tribes were also used, such as Cherokee, Choctaw, Lakota, Comanche, and others, but the Navajo code is by far the most famous (and also probably the best and most used).
The Official Site of the Navajo Code Talkers is a great resource, as is Code Talker: The First and Only Memoir by One of the Original Navajo Code Talkers of WWII by Chester Nez.
“That is why it was called Babel —because there the Lord confused the language of the whole world.”