The Navajo language was chosen to
code U.S. military operations because
it has no written form and is almost
impossible for non-native speakers to
learn. After the operation was
declassified in 1968, the Japanese Chief
of Intelligence admitted that though
his army had been able to decipher
many U.S. codes, they were never
able to crack the Navajo code. Source Source 2
And the irony is that if the U.S. government had gotten their way, there would have been NO Navajo speakers at all by WWII. First Nations Children were forcibly taken to “Indian schools” for decades starting in the 1890s, where they were viciously punished for speaking a word of their own language. The fact that the language survived to become an asset to the country that tried to kill it doesn’t get mentioned often.
It’s very important that the above comment be reblogged along with the OP information.