Film set in a WW2 prisoner of war camp, maybe made in the 1950s or 1960s.
It focuses on the efforts of the inmates to escape and there is one who decides to pretend to be insane in order to be repatriated home. He fools the Germans and gets sent home but the film ends with a letter from his wife saying how he accepts his condition (so he has actually gone mad).
Can anyone put me out of my misery and identify this film please?