The combination of these two systems — the military vocabulary and the substitution alphabet — created something that was, in the context of 1942 Pacific communications, essentially unbreakable in any practical timeframe.

Consider what would have been required to crack it.

A Japanese cryptanalyst intercepting Navajo Code would first have to recognize that the language was Navajo — itself not obvious to listeners unfamiliar with North American indigenous languages.

They would then have had to find speakers of Navajo — an extraordinarily rare resource in Imperial Japan, which had essentially no relationship with the Navajo Nation or any North American tribe.

And even if they had found a Navajo speaker, that speaker would have encountered not natural Navajo but a code built on top of Navajo, using words in specialized ways that did not correspond to their natural meanings.

The word for hummingbird was not being used to communicate anything about hummingbirds.