The Navajo language is incredibly complex, with syntax, tonal qualities and dialects that render it unintelligible to outsiders. A spoken language, it has no alphabet or symbols, and is used only in remote Navajo areas of the American Southwest. For these reasons, it was selected as a code language during World War II by the U.S. Marines.
In 1942, Japanese translators and codebreakers were regularly intercepting U.S. military communications and sabotaging U.S. plans in the Pacific. Philip Johnston, a white man who was raised on the Navajo Reservation, convinced Major General Clayton Vogel, commanding general of the Amphibious Corps, Pacific Fleet, that the Marines should recruit Navajos to transmit important military communications.
Image from Wolfgang Staudt.