The movie does fall into some predictable patterns – portraying British characters as spirited, the French as chaotic, the Dutch as reserved, and the Poles as generally eager – so it's best viewed as an engaging story inspired by true events rather than a serious examination of the facts. Nevertheless, it effectively conveys the sense of hopelessness and irritation that must have been present when the prison doors slammed shut, leaving freedom just out of reach. Eric Portman and Lionel Jeffries are standouts in my opinion; I’ve always felt John Mills came across as slightly too self-assured. When the castle reaches its full capacity and the prisoners begin working together, it truly becomes a superb illustration of what's possible when people are determined. There are also some genuinely funny moments – the "croque mort" line still gets to me.

Source on TMDB