A & E aired a documentary a while back. The "code" was, esentially, the Navajo Language with certain words and expressions changed so that it was actually a code within a code. For example, hand grenade = potato. The chances were several billion-to-one the Japanese would have someone who could speak Navajo but, amazingly, they did. A U. S. Soldier, a full-blood Navajo who had been captured in the Philippines in 1941, was brought from a labor camp in Occupied China in an unsuccessful attempt to break the code. He spoke Navajo fluently but couldn't follow a conversation sufficiently to fully understand the messages. The "code" was classified for more than twenty years after the war ended in the possibility it may have been needed again. This was - and remains to this day - the only code in history that was never "broken" by the enemy.