Autumn 1941. The crew of the U 96 celebrates its last day on land in La Rochelle, France. The exuberance of the men is nothing more than the fear of the next mission, which could be the last. War correspondent Lieutenant Werner does not understand the apparent cheerfulness, as he does not yet know the pitiless harshness of the war in a cramped submarine.

The U 96 crew has been running on patrol south-west of Ireland for days. Monotony, inactivity, and boredom on board are transformed into aggression. A message about a convoy changes the mood of the crew. The "old man" risks a periscope attack. Surprisingly, a destroyer emerges, which hunts the submarine with depth charges.

For almost four weeks, the submarine is traveling south-west of Ireland and is held underwater by a destroyer during its first attack on an English convoy. Exploding depth charges hurl the crew and submarine into chaos. But the "old man" succeeds in maneuvering U 96 out of the danger zone. Subsequently, the submarine gets into a storm period lasting more than three weeks.

The U 96 encounters a convoy and sinks three cargo ships with its torpedoes. Then a 24-hour pursuit of the submarine begins with two destroyers dropping depth charges. The "old man" tries to escape in 230 meters of water depth. The end for U 96 seems to have come.

The U 96 has been dispatched to the Mediterranean. After picking up supplies in the Spanish town of Vigo, the journey to Gibraltar begins. An aviation attack during the nightly crawl and cruising British ships force U 96 to a neck breaking dive - at 280 meters depth the submarine hits the bottom of the ocean.

The submarine is heavily damaged, lying on the ocean floor in a depth of 280 meters. Despite the seemingly hopeless situation, the crew starts with repair work and dares an attempt to emerge. After tormented tension the U 96 finally breaks off from the ocean floor.