Joan consoles Knowlton for the death of Walters and says she loves him but also good-bye. Joan leaves with her father. At sea Toler argues with Knowlton about Joan but blames himself for bringing it up. Knowlton fires the torpedoes himself, sinking two of the three ships. Toler puts Knowlton under arrest.
Depth charges causes the sub to leak water.
Toler orders the sub to the bottom. Knowlton discovers chlorine gas and closes off that section. Toler orders the sub up, but the engine won't start. Forgotten by MacDougall, Jenks is left to suffocate in order to save the rest. As oxygen gets low, one man shoots himself.