The American South during the Civil War in February 1864: Charleston Habor is under siege. Cut off from all supplies, the Confederates decide to bring a secret weapon into use that has never been tested before. The C.S.S. Hunley, the first submarine in history, is assigned to sink the U.S.S. Housatonic that anchors outside the habor and thus put an end to the blockade.
Al previous attempts to put the submarine into action have failed killing the entire crew. Therefore the project was due to be cancelled but the futile situation calls for whatever means available. A crew combined of "hopeless" cases volunteers for the suicidal mission. Lieutenant George Dixon, who expects nothing of his life anymore since his wife has died, and his eight-men crew - all sailors with "disciplinary problems" - start to train for their mission. The technical problems alone are numerous: ventilation on board hardly works and the compass is useless for navigation because of the boat`s steel body, let alone the torpedo which as dangerous for the enemy as for the crew itself.
Driven by mere power of the men`s muscles the submarine puts to sea in the night of Febuary 14th.