King Rat (1965): similar in plot in a way to La Grande Illusion (which I haven't seen), an American hustler (played by George Segal) ends up running a Japanese prisoner of war camp. At the end Segal's character is better fed and dressed than even the Japanese are, but the 'realities' of social class are reasserted when the camp is liberated. Based on the eponymous book by James Clavell (1962).