John Ford welded four of Eugene O'Neill's one-act plays about the sea, Bound East for Cardiff, The Long Voyage Home, The Zone, and Moon of the Caribees, into this melancholy film about wayfaring seamen, changing the setting from the turn of the century to WWII. This was O'Neill's favorite of the films based on his work, and he watched it often enough to eventually wear out his print.
After a night of revelry in the West Indies, the crew of the SS Glencairn return to the tramp steamer and set sail for Baltimore. They're a varied lot, from middle-aged Irishman Driscoll (Thomas Mitchell), to the young Swedish ex-farmer Ole Olsen (John Wayne), to the brooding Lord Jim-like Englishman Smitty (Ian Hunter).
After the ship picks up a load of dynamite in Baltimore, the rough seas they encounter become especially nerve-racking to the crew, who are also concerned that Smitty might be a German spy.