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Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

EDIT: This edit is based on some of the commentary on the other answers. When I wriotewrote my answer, I assumed that the Japanese (I guess the Navajo code-talkers were used in the Pacific) would have to learn the obscure language on their own, without reference to prior research on the Navajo language. Some of the other answers have asserted that there was plenty of research available, including dictionaries. I still think that research would have been very, very hard for the Japanese to put their hands on in the middle of a war.

Still, I have to admit that this is a case of security through obscurity, albeit a very though case to crack. I still think it was a better plan than the alternatives, in the wartime theater where it was used. It was quick to set up, and gave the US a longer period of safe communications through field radios than any viable alternative. And, as I said, the cost on the US coders was low, while the cost on the Japanese crackers was high.

Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

EDIT: This edit is based on some of the commentary on the other answers. When I wriote my answer, I assumed that the Japanese (I guess the Navajo code-talkers were used in the Pacific) would have to learn the obscure language on their own, without reference to prior research on the Navajo language. Some of the other answers have asserted that there was plenty of research available, including dictionaries. I still think that research would have been very, very hard for the Japanese to put their hands on in the middle of a war.

Still, I have to admit that this is a case of security through obscurity, albeit a very though case to crack. I still think it was a better plan than the alternatives, in the wartime theater where it was used. It was quick to set up, and gave the US a longer period of safe communications through field radios than any viable alternative. And, as I said, the cost on the US coders was low, while the cost on the Japanese crackers was high.

Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

EDIT: This edit is based on some of the commentary on the other answers. When I wrote my answer, I assumed that the Japanese (I guess the Navajo code-talkers were used in the Pacific) would have to learn the obscure language on their own, without reference to prior research on the Navajo language. Some of the other answers have asserted that there was plenty of research available, including dictionaries. I still think that research would have been very, very hard for the Japanese to put their hands on in the middle of a war.

Still, I have to admit that this is a case of security through obscurity, albeit a very though case to crack. I still think it was a better plan than the alternatives, in the wartime theater where it was used. It was quick to set up, and gave the US a longer period of safe communications through field radios than any viable alternative. And, as I said, the cost on the US coders was low, while the cost on the Japanese crackers was high.

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Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.  

EDIT: This edit is based on some of the commentary on the other answers. When I wriote my answer, I assumed that the Japanese (I guess the Navajo code-talkers were used in the Pacific) would have to learn the obscure language on their own, without reference to prior research on the Navajo language. Some of the other answers have asserted that there was plenty of research available, including dictionaries. I still think that research would have been very, very hard for the Japanese to put their hands on in the middle of a war.

Still, I have to admit that this is a case of security through obscurity, albeit a very though case to crack. I still think it was a better plan than the alternatives, in the wartime theater where it was used. It was quick to set up, and gave the US a longer period of safe communications through field radios than any viable alternative. And, as I said, the cost on the US coders was low, while the cost on the Japanese crackers was high.

Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.  

Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

EDIT: This edit is based on some of the commentary on the other answers. When I wriote my answer, I assumed that the Japanese (I guess the Navajo code-talkers were used in the Pacific) would have to learn the obscure language on their own, without reference to prior research on the Navajo language. Some of the other answers have asserted that there was plenty of research available, including dictionaries. I still think that research would have been very, very hard for the Japanese to put their hands on in the middle of a war.

Still, I have to admit that this is a case of security through obscurity, albeit a very though case to crack. I still think it was a better plan than the alternatives, in the wartime theater where it was used. It was quick to set up, and gave the US a longer period of safe communications through field radios than any viable alternative. And, as I said, the cost on the US coders was low, while the cost on the Japanese crackers was high.

2 edited body
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Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get itis a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get it a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

Code talking in an obscure language puts two layers of encryption on the message. The first layer is that it's a language. The second is that it's a code. The code part is usually pretty simple with code words replacing the real words. The phrase "Omaha beach" is simple code. The place we called Omaha beach probably has an actual name in French or German. Oral codes based on simple word substitutions are easy to crack, given enough coded messages, and some inkling of the underlying subject matter.
Deciphering an unknown language is enormously difficult, even after you realize that it is a language. It can take months to figure out the variations in normal speech. For example, verb tenses might work differently in Navajo language than in English or German. Word order might be different, and in a context dependent way. To a native speaker, this transformation is easy to do in real time, without much mental effort, except when some concept is difficult to convey. The military messages in the field are usually easy to convey in another language. They involve place, time, and action.
So what you get is a high cost on the would be interceptor and a low cost on the encoder-decoder team.
The wikipedia article (see Code Talker) mentions the two layers in passing. It also provides more details, like what languages other than Navajo were used.

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