STALAG 17 (1953)

After two Americans are killed while escaping from a German P.O.W. camp in World War II, the barracks black marketeer, J.J. Sefton, is suspected of being an informer.
In a German prisoner-of-war camp named Stalag 17, one of its compounds holds 630 American airmen (all of whom are sergeants) and is overseen by camp warden Colonel von Scherbach.
In December 1944, the men of Barracks 4—led by appointed barracks chief "Hoffy" Hoffman and security officer Frank Price—arrange for the escape of fellow airmen Manfredi and Johnson. The two are shot dead in the attempt, and the men believe they were betrayed by an informant. Suspicion falls on an enterprising cynic who barters openly with the German guards for various luxuries. He also creates profitable ventures that distract from the mundanity of camp life, from organizing mouse races for gambling, to an improvised distillery for brewing alcohol, to a makeshift telescope to view the Russian women from a neighboring compound. Clarence "Cookie" Cook, who narrates the story, serves as Sefton's underling.
The men of Barracks 4 do their best to keep sane, which includes enduring the antics of barracks clowns "Animal" Kuzawa and Harry Shapiro and smuggling in a radio to listen in on war news. Their jovial German supervisor, Sergeant Schulz, secretly retrieves hidden messages from a hollow black queen on the chessboard, and straightens the looped cord of a dangling light bulb, which serves as a signal between himself and the informant.