b) Navajo

The Navajo language was used as a code by the U.S. military during World War II. The code, developed by the Navajo Code Talkers, was never broken by the Japanese and played a crucial role in secure communications in the Pacific Theater. The use of the Navajo language, which was unwritten and known only to a small group of people, demonstrated a unique and successful application of indigenous language and culture in military operations.