The Navajo Code Talkers program was proposed and implemented at the beginning of WWII by Philip Johnston. Johnston was a WWI vet that was raised on a Navajo reservation and was one of only about an estimated 30 non-Navajo’s who could understand the language.
The reason the Navajo language was so appealing was because of the complexity and uniqueness of the grammar, dialect, and the language itself. It was an unwritten langue and so complicated even the closest of other tribes could not understand it. It was approved after a demonstration Johnston had set up where he demonstrated, under simulated combat conditions, that Navajo men code encode, transmit, and decode a 3-line message in 20 seconds. Given the technology at the time, this same message would take approximately 30 minutes to do with machines.
Most of the code was a variation on the military’s phonetic alphabet, although specific code words were given to more commonly used military terms and definitions (I.E. “silver oak leaf” given to the rank of lieutenant colonel).
During the first few days of Iwo Jima Major Howard Connor of the 5th Marine Division had Navjo Code Talkers working around the clock and would later credit them to the victory, saying “”Were it not for the Navajos, the Marines would never have taken Iwo Jima.”
The deployment of the Navajo code talkers continued through the Korean War and after, until it was ended early in the Vietnam War. The Navajo code is the only spoken military code never to have been deciphered.