In 1943 the world was at war, and no one was sure who was going to win. Japan had a stranglehold on Asia, and German forces were running rampant throughout Europe.
A specially trained group of officers allowed themselves to be captured because they knew they would be sent to one of two prisoner of war camps. Their plan was to escape the POW camp and meet with local Nazi sympathizers and commandos who arrived by submarine. They would then travel to a major waterway and destroy a refining and fuel storage facility which would greatly reduce the enemy's ability to continue the war.
The problem was the POWs were German. The camp was in Louisiana. The waterway was the Mississippi River. Only one man knew the entire operation and he was a double agent.