And this was made into a terrible, terrible movie with Nicolas Cage.
Originally posted by Carlos
Their secret: a few brave indians (can't remember, but maybe Dakota), who spoke a very rare language (spoken by only a few hundred people in the world )who were taught english. The original english message was translated to their own language - which has a very hard and weird grammar and pronunciation - sent it this way, then the "encoded" message was translated by the receiver - who was of course also an indian - to english.
The japanese were having hard times trying to decrypt those messages, but never managed to understand a word!
This method has also it's weakness, as the japanese could have captured one of those people, but apparently this did not happen.