It was early morning on a Sunday in October 1923. U.S. Submarine O-5 was leading a patrol of four subs in a bay off the northern end of the Panama Canal. Suddenly the lead sub was violently struck by a steamship. Amid the ensuing chaos one of the O-5 sailors, Henry Breault, escaped to the sub’s deck. But then he remembered that one of his buddies was still below. He had a split second to decide what to do next.