How close was Japan to cracking Navajo code talkers? Was Japan aware Americans were using a Native American language as code?

I did a research project with Navajo sources on this. It sadly never was finished and published, but I was able to use local archives, talk to members of the Navajo community about their verbal histories and study the US military documents regarding the code. I was also studying Navajo Language at time as I am not Navajo or a member of any tribe.

Four separate things kept the Navajo code from being cracked. In order of importance, this was the code itself, the Navajo language, it's use, and the Japanese intelligence community.

The code itself was relatively simple and was a glorified slang with a weird syntax. With applications for the military alphabet. Here is an example of ship names provided by the CIA https://www.cia.gov/news-information/featured-story-archive/2008-featured-story-archive/navajo-images/Navajo-ships.jpg/image.jpg. In English or any other language this could be cracked with time. Imagine a modern US infantry squad calling for "Apache support". To someone without knowledge of US weapon systems, this would seem like a very strange request. However after a few times hearing that and having helicopter gunships show up, the link could be drawn and part of the code could be cracked.

The next step in encryption that kept it safe was the language itself. Navajo is certainly one of the most difficult languages in the world to learn. Very very few non-Navajo have ever been nearly fluent in the language. Navajo heavily relies on inflections of tone and use of nasal noises on vowels, so simple changes in pitch of a vowel mean a completely different word. It is also extremely specific on conjugating verbs, using singular, dual and plural. Among many other complexities.

Navajo was (it's doing much better now due to many programs and educational outreach), a dying language and very few texts on it existed at the time. It's language family is the Athabaskan language, composed of a few other tribal languages in the American SW and several in central and western Canada. This is not a language where one could go pick a book off the shelf.

There was a Navajo POW in Japanese captivity, Joe Kieyoomia, who was not part of the Code Talker program. He was forced to listen to the transmissions by his captors. The Japanese had studied the Navajo transmissions and had narrowed it down through a lengthy process (I cannot understand Japanese so I was unable to read the primary sources on this, sorry for the vagueness), to figure out that it was Navajo. Kieyoomia listened into these transmissions and heard phrases like "Red soil ahead" among all of the organizational information that was also coded. He thought it was complete gibberish, and told the Japanese that it made no sense. The Japanese thought he was lying, and I'll get into their response more to the code later, and tortured him regularly in an attempt to get more information about the Navajo language and code out of him.

Third, the Navajo Code was a tactical, and very rarely strategic code that was only submitted verbally. The Navajo Code was never used in a written form. If it had been, it could have been subjected to the same methods of code breaking that the world was using on operational and strategic codes like Enigma. The Navajo code was far less complex than Enigma and would not have held up well to such attacks. Audio recordings on wax cylinders were expensive and difficult to maintain in the Pacific theater, so even recording the radio messages that the Code Talkers sent was incredibly difficult.

The Navajo Code was not only used on a tactical level, but on a much smaller scale than US operational codes. When the Code Talkers program was under development, it's major selling point wasn't it's heavy encryption, but time. The current way for US forces to communicate on a open level was either "in the clear", i.e. just over the radio, or to use an encoding machine that usually took about an hour to encode and decode messages. The latter wasn't great when you needed fire support, and the former the Japanese heavily exploited with their relatively high percentage of fluent English speakers. They did so both gathering intelligence on American activities and sending false messages to sew confusion and disorder.

Code Talkers on the other hand, could communicate messages to other Code Talkers nearly instantly. Fire support, movements, positions, could all be transmitted nearly "in the clear" in terms of speed. Also, Code Talkers worked like a sort of passcode, or key. With Navajo being so complex and the Code Talkers being such a small group, they were able to absolutely recognize and know each other during transmissions. And once attached units also recognized this, Code Talkers messages were treated as critically important, the Japanese couldn't falsely transmit them. There are cases of false Japanese messages being sent out as if they were American, and then Code Talkers letting everyone know of the real situation. This uniqueness kept the code in the military arsenal (and the Navajo language was classified) until 1965, when frequency hopping radios started to become available and replaced the Code Talkers concept.

Finally, the Japanese Intelligence Community. I again, do not understand Japanese, so none of this is a primary source and I won't go into much detail as it is not my expertise. The Japanese Intelligence Community was an absolute shambles. The Army/Navy rivalry was replicated between the different organizations, resulting in no real clear unified efforts and quite a few efforts to steal glory from each other. There were more focused on American operation codes that were transmitted in text, far more regularly and often and contained more information. It also seems that Kieyoomia's resistance to Japanese efforts also led the Japanese to believe that it really was just the language, and such limited their code breaking efforts there.

The Navajo (and others!) Code Talkers provided a critical role for the Allied war effort. Much of the information on the Code Talkers is still only in verbal histories. There are many issues regarding Tribal Sovereignty around collecting this information and publishing it, so information can be hard to come by. I highly respect those issues and recommend you all do too.

Thanks!

As a post script, the Germans actually sent Anthropologists to the US during the inter-war to study Tribal languages after the success of similar Tribal Code Talkers in WW1. I have been unable to find if this information was ever put to much use, as other tribes' Code Talkers were used in the European Theater.

Edit: Thank you for the gold, but please, please stop. I wrote below about the commodifying of cultural knowledge, and this is exactly what I was speaking about. I give this knowledge freely, and ask that if interested, you all check out Navajo sources for more info! Or just go check out r/Navajo to see what the Navajo Nation is like today!

Also, this wasn't a thesis project or anything big like that, it was just a semester undergrad research project that I really felt a calling to. I apologize for any confusion there.

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