Answer: The correct answer is : Philip Johnston
Explanation: Johnston was a civil engineer who grew up speaking Navajo, a language that is rarely used outside of reserves. When he could no longer fight in the Second World War because of his age, he had the idea of having a secret code in Navajo and proposed this to the US Marine Corps, after doubts and tests, Johnston finally convinced them and they were initially recruited 30 Navajos specialized in telecommunications.