1942: Navy war correspondent Lt. Werner is assigned to submarine U96. He is ordered to accompany the crew on a mission in the Atlantic ocean and to produce some heroic reporting. Werner, a critic of the nazi regime, meets a crew consisting of quite diverse characters: the laconic-sarcastic captain, a firm patriot but not a nazi, the silent chief engineer who permantly worries about his family at home, the first leutenant, an ambitious young nazi.
After weeks of fruitless searching in the vastness of the Atlantic, the crew finally sinks an enemy ship. But soon the situation changes and the hunters become the hunted. The allies have equipped their destroyers with ASDIC, a submarine tracking device. U96 is no longer safe in the depths and is frequently attacked by enemy vassels.
After their successful mission the boat heads for the home base in France but before reaching the safe habour receives new orders to enter the Mediterranean Sea. In the Gibraltar straits U96 is discovered, hit and sinks to the bottom of the sea. After days of exhausting repair works, running low on oxygene, and increasing tension among the crew members, the men eventually manage to refloat the boat. Severely damaged the boat reaches its home base. In the very moment when the boat docks at the quay a large part of the crew is killed by allied dive bombers.