Someone sent me an inquiry re the above and I thought I'd share part of my response.
" . . . 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 fluent Navajo 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."
It's truly astounding how resourceful we can be (or, at least, some of us) when the chips are down.