system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What was it about Navajo Code talkers that made their signals so hard to decrypt in WWII?

I hear about how cool these guys were and how much of a help they were in WWII, but what is it about the Navajo language that makes it such a good code?
gpt
English is related to German, Italian, and most European languages that were relevant in WWII, and plenty of them knew English anyway.

Navajo, on the other hand, has been separated from other world languages for so long that any sort of pattern that could be derived from being a related language wasn't present. Even most other Native American languages are so distantly related that they aren't a great guide. It also wasn't well documented, so there were no resources for the enemy to turn to, even if they suspected Navajo. On top of that, the code talkers didn't use plain Navajo, but a code based on Navajo, so that it'd still be difficult to decipher if a random Navajo speaker were captured. So it was basically a difficult code on top of a difficult code.