The Navajo code talk in WW II was a childishly easy code to break

The code does seem really easy to break. From https://www.nationalww2museum.org/war/articles/american-indi...:

[The first type of code they created, Type 1 code, consisted of 26 Navajo terms that stood for individual English letters that could be used to spell out a word. For instance, the Navajo word for “ant,” wo-la-chee, was used to represent the letter “a” in English.

Type 2 code contained words that could be directly translated from English into Navajo, and the code talkers also developed a dictionary of 211 terms (later expanded to 411) for military words and names that didn’t originally exist in the Navajo language. For example, since there was no existing Navajo word for “submarine,” the code talkers agreed to use the term besh-lo, which translates to “iron fish.”]

If you were listening to Type 1 code, you would hear the same 25 words over and over again. Then if you replace each word with an English letter according to English language letter frequency, you are done.