More corrections:
The Navajo "Code Talkers" were Marines, not Army.
The Navajo "Code Talkers" spoke in their native language and there was no
need to further encrypt it. While the Japanese had sent people to American
Universities and American Language Schools before WW2, none had studied the
Navajo language and as far as the Japanese were concerned, the radio
transmissions were in code, which they couldn't break. Since the "Code
Talkers" were talking in "Plain" Navajo, there was no need to change a "code"
daily.
What the Navajos had to do was to come up with terms for military specific
equipment or procedures for which there was no equivalent term in the Navajo
language, such as "tank," "landing craft," "flame thrower," etc. Some of the
terms, using only words that were already in the Navajo language, were quite
convoluted. (Something similar to the border Spanish "trucka" for "truck"
wouldn't do.)
Roger Turk
Tucson, Arizona USA