Jerry wrote:
> In turn, the top-security encryption used by the U.S. during WWII was
> never compromised.  The message was first translated into the Navajo
> language then encrypted.

As far as I know, Navajo was never used for written cryptography as it
wouldn't be that hard to break (you would quickly learn which was the
picturesque Native American word for "aircraft carrier" and so on).

The military did employ "Code Talkers" from the Navajo (and later
Choctaw and possibly other) nations who manned the radios
during assaults by the U.S. Marines.  This provided real time
"encryption" for tactical command and control which would otherwise
have taken place "in the clear" (i.e. in English).  Even if you wrote
down the intercepted traffic the data would no longer have any value
by the time you got some idea of what the message had meant.

These Native American languages were complex, unusual, and very obscure.
"Breaking" these codes would require not only someone who was a fluent
speaker of the language, but also one who understood the local tribal
slang employed, as the people on either end of the connection typically
had grown up together in the same place.

A quick STFW on "code talkers" reveals some details at:

   http://www.history.navy.mil/faqs/faq61-2.htm

G.