A couple posts down, I discussed the death of the original code talkers, Chester Nez. LINK
and mentioned a Navajo who was a NMNG POW who refused to help them break the code.
His name was Joe Kieyoomia. From Wikipedia.
When the "Navajo Code" had the Japanese baffled, Kieyoomia was questioned and then tortured, although he could only understand bits and pieces of what trained Navajo Code Talkers were saying, the code was so sophisticated that he eventually told the Japanese that it sounded like nonsense to him.
Kieyoomia was not trained as a code talker and did not know about the code. Stripped naked and made to stand for hours in deep snow until he talked, Joe Kieyoomia's feet froze to the ground. Finally allowed to return to his cell, a guard shoved him, causing the soles of his feet to tear.
After surviving the prison camps, the "hell ships" and the torture, Kieyoomia was a prisoner in Nagasaki when that city was the target of the second atomic bomb dropped by the U.S. Army Air Forces (USAAF). Kieyoomia survived the attack saying he was protected by the concrete walls of his cell. After 3½ years as a prisoner of war, he was abandoned for three days after the bombing, but says a Japanese officer finally freed him. He returned to the United States.