What are all of the ways the aircrew were convinced to talk?
In 1944, German intelligence strives to find the target of an upcoming raid by the reputed "B-99 bomber". To achieve this end, they interrogate a recently shot-down aircrew from a B-99 reconnaissance mission that was shot down over Italy. The aircrew is sent to Dulag Luft POW camp.
The German officers, commanded by Major von Behn use various methods to discover this information, some of them quite subtle. While interviewing Lieutenant Frank L. Williams, Jr. and Captain James Spencer, the two airmen at first resist any probing for information. Other members of the crew include Sergeant Alfred Mason.
Though no physical brutality is used, the Germans at one point stage a mock execution to scare a prisoner. Another prisoner is subjected to isolation to heighten his fear. Red Cross officers and a nurse use their positions to extract information from the prisoners.  Each airman eventually provides useful information because of their arrogance, fear or naivety. Some of what they say, which the enemy finds useful, seems innocuous but is used by the Germans as pieces to solve the larger puzzle.
In the end, the Germans are able to determine the target of the raid and the B-99 bombing mission is intercepted. The intended target is spared heavy damage with 21 B-99s shot down and the loss of 105 aircrew. 
The U.S. intelligence officer  (Lloyd Nolan) in his briefing to the surviving members of the raid, stresses not to talk under any circumstances, concerned that the danger of talking too much, even innocuous conversation can help the enemy. He also states not to let down one's guard, that everything in a prison camp is suspect, and to not try to outwit the enemy.
stage a mock execution isolation Red Cross officers and a nurse use their positions