 During World War II, the Allies were having trouble against the German Navy especially their U-Boats because of their highly sophisticated cipher machines. When a German U-Boat is damaged and is waiting for assistance, the Americans decide that this is an opportunity for them to get the machine. So they have one of their subs made up to look like a German, and plan to pretend to be the ship sent to assist them and take control of the U-Boat and take the machine and destroy the sub so that the Germans will not know that they have the machine. And everything went according to plan; they got the machine and transferred the crew to their sub and were about to leave when out of nowhere they re hit by a torpedo from the German relief sub. The members of the crew who were not on board the sub, proceed to board the German U-Boat and try to make it back. Now the senior officer is the sub s XO who s eager to be in command but his commander had told him earlier that he felt he was not ready because he might not be ready to make tough decisions. And now he has to, if he and the survivors are to survive.