Navajo Code Talkers: World War II
Guadalcanal, Tarawa, Peleliu, Iwo Jima: the Navajo code talkers took part in every assault the U.S. Marines conducted in the Pacific from 1942 to 1945. They served in all six Marine divisions, Marine Raider battalions and Marine parachute units, transmitting messages by telephone and radio in their native language a code that the Japanese never broke.
The idea to use Navajo for secure communications came from Philip Johnston, the son of a missionary to the Navajos and one of the few non-Navajos who spoke their language fluently. Johnston, reared on the Navajo reservation, was a World War I veteran who knew of the military's search for a code that would withstand all attempts to decipher it. He also knew that Native American languages notably Choctaw had been used in World War I to encode messages.
Johnston believed Navajo answered the military requirement for an undecipherable code because Navajo is an unwritten language of extreme complexity. Its syntax and tonal qualities, not to mention dialects, make it unintelligible to anyone without extensive exposure and training. It has no alphabet or symbols, and is spoken only on the Navajo lands of the American Southwest. One estimate indicates that less than 30 non-Navajos, none of them Japanese, could understand the language at the outbreak of World War II.
The Navajo Code Talker's Dictionary
When a Navajo code talker received a message, what he heard was a string of seemingly unrelated Navajo words. The code talker first had to translate each Navajo word into its English equivalent. Then he used only the first letter of the English equivalent in spelling an English word. Thus, the Navajo words "wol-la-chee" (ant), "be-la-sana" (apple) and "tse-nill" (axe) all stood for the letter "a." One way to say the word "Navy" in Navajo code would be "tsah (needle) wol-la-chee (ant) ah-keh-di- glini (victor) tsah-ah-dzoh (yucca)."
Most letters had more than one Navajo word representing them. Not all words had to be spelled out letter by letter. The developers of the original code assigned Navajo words to represent about 450 frequently used military terms that did not exist in the Navajo language. Several examples: "besh- lo" (iron fish) meant "submarine," "dah-he- tih-hi" (hummingbird) meant "fighter plane" and "debeh-li-zine" (black street) meant "squad."
http://www.history.navy.mil/faqs/faq61-2.htm