Radio communications made it much easier to direct troops in combat and react to events as they happened. During World War II, though, radio was still new enough that it was easy for opponents to intercept the signals of America and its allies. In order to prevent such interceptions and protect the troops, America used different types of codes over the airwaves. The Navajo language proved to be the basis for an unbreakable code.

Technological Limits

Modern radio communications mostly use digital signals. A digital signal is transformed into a code for broadcast, and then re-translated into data on the receiver. Since it begins as a code, even if it is intercepted all one can hear is static without the decryption key. The signal itself is encrypted, or coded. Analog sends the data itself over the airwaves. If it is intercepted, one can hear what is being sent. In World War II, all military radio applications used analog signals, which were easy to intercept.

Military Coding

Rudimentary efforts were made to encrypt analog signals, but these involved adding other sounds to the original signal. This often made it difficult for the intended receiver to understand the message. The most effective way of preventing the enemy from gathering valuable information from intercepted radio signals was to send the message itself in a form of code. That created another hurdle, but code-breaking techniques had become a specialty in military intelligence circles in World War II. What was needed was a system that was not dependent on normal rules of grammar in order to make the code secure from techniques of analysis.

Navajo Language

Philip Johnston, a World War I veteran who had been raised on a Navajo reservation, proposed using the language as an unbreakable code. Navajo is a tonal language, which means that the pitch in which words are said is critical to the meaning of those words. Its structure is radically different from any European language, and little was known about it outside the United States. Navajo speakers were recruited from reservations for special duty to use the language in the transmission of radio messages.

Development and Implementation

To perfect the code, the Navajo recruits built a vocabulary by substituting normal Navajo words for military equipment, such as specific types of tanks and planes. To add yet another layer of difficulty to the code, some Navajo words had to be decoded back to their English equivalents, to make an alphabetic English language code that was transmitted via the Navajo language. The Navajo code-talkers all served in the United States Marines. They were distributed throughout units in various areas of the war, usually as two-man teams, to send and receive messages. About 400 served in the Marines. The program proved so successful that it remained classified until the early 1990s, when the many brave Navajos who participated were finally honored for their unique service.