Today is National Navajo Code Talkers Day. Four surviving code talkers were honored in the Navajo Nation's capital. | U.S. Marine Corps

The Code Talkers used native languages to send military messages before World War II. Choctaw, for example, was successfully used during World War I. But the Marine Corps needed an “unbreakable” code for its island-hopping campaign in the Pacific. Navajo, which was unwritten and known by few outside the tribe, seemed to fit the Corps’ requirements. Twenty-nine Navajos were recruited to develop the code in 1942. They took their language and developed a “Type One Code” that assigned a Navajo word