[1] In a New England port town, Pop Thorson (Wallace Beery) and Rocky Blake (Chester Morris) are rival tugboat owners.

Thorson does not take well to naval discipline, particularly when his superior officer, in charge of the fleet, turns out to be Blake, who is now a lieutenant and dedicated to his duty.

On their first mission, Thorson correctly reasons that any submarine would avoid the storm-wracked area where they were ordered to patrol, and would be in the lee of Nantucket Island.

But the German captain tricks the inexperienced Thorson into breaking off his attack by releasing oil from his vessel, and sinks a lightship before leaving.

As they wait silently, he seizes an opportunity to shut himself in a room and bang on the hull with a wrench, telling the listening sub chasers where to find the sub.

The film ends with Thorson receiving the Medal of Honor, restored to the rank of ensign, and again commanding a sub chaser, to the delight of Susan and the residents of the port.