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Navy officers "Butch" Rogers and "Sock" McGillis, former rivals for Ann Sawyer, are reunited with Ann and her fiancé, Tom Callam, at the U.S. Naval Sub-base off Connecticut, from where the U.S.S. Dolphin , called Submarine D-1 , will make her maiden voyage. After Tom is killed when his submarine sinks during a drill, Butch promises to be Ann's guardian, while determined to modernize the submarine navy with a rescue chamber. Butch is then made chief of the D-1 , which will sail to San Diego through the Panama Canal under Lt. Comm. Dan Matthews, an old friend of Butch who needs the success of the D-1 for a navy promotion. Sock and his friend Lucky join the crew of the D-1 for a free ride to San Diego, where Ann has been transferred, and where Lucky plans to meet his fiancée Arabella, who will only marry him if he wins the lottery. En route to Panama, Sock's cocky attitude puts the crew in danger when he floods the main ballast valves and the D-1 is unable to surface, delaying her arrival in Panama. After the D-1 arrives in San Diego, Matthews transfers Butch to the U.S.S. Holland to perfect his rescue chamber and makes the admonished Sock chief of the D-1 . When one of the D-1 's crew is hurt during combat maneuvers, Butch's rescue chamber saves the injured man and Sock just in time. Matthews and Butch then receive accolades from the Bureau of Navigation when the D-1 is recommissioned. Sock wins Ann for a wife, while Lucky wins the lottery, only to find that salt water has erased the winning numbers; Arabella then refuses to marry him.