Young war correspondent Lt. Werner is assigned to join German Submarine U-96 on its next patrol in the Atlantic.

As the excitement and anticipation of conflict slowly fades, the crew of U-96 is faced with an unforeseen enemy: boredom. The monotonous long stretches without action create tensions among the crew until a coded signal from U-32 presents an opportunity.

The Captain’s gamble against the Destroyer fails and exposes the crew to the horrors of depth charges. Despite surviving with serviceable damage, an outbreak of crabs and a three-week Atlantic storm test the limits of the occupants of U-96.

The crew's jubilation at sinking three ships is short-lived as they switch to silent running to avoid the British Destroyers using Sonar to find and attack them. Later, a triple encoded signal from headquarters interrupts their plans.

A detour to neutral Spain allows the submarine's crew a short break before continuing on their dangerous mission through the Gibraltar Strait.

In spite of surviving a calamitous crash dive, U-96's extensive damage threatens the chance of her crew ever seeing the surface again.