there is the louis zamperini story. He was an aviator in WWII for the USA and then became a prisoner of war in Japanese hands.

There are books and movies about him and one of the books is Unbroken.

In this context, unbroken seems to mean submitting successfully to an endurance trial.

It appears he became a Christian after the war and so there are Christian biographers also who enjoy reading and telling his story.

Unbroken (The Young Adult Adaptation): An Olympian's Journey from Airman to Castaway to Captive Paperback – Illustrated, April 25, 2017