James Caan stars as Lt. Commander Richard Bolton, who must lead a group of midget submarines in daring raid on a German battleship. A special group of navy divers is created when a disabled Nazi warship is discovered in a fjord in Norway. Commander Bolton is the Canadian expert designated to train the new unit. Their mission is to plant a bomb on the warship as it undergoes repairs. The hard-driving Bolton encounters resentment from the British soldiers he trains, but he ultimately earns their respect as a leader. Their intense training operation is interrupted by an attack of Nazi paratroopers just before the unit leaves for Norway. Spectacular underwater photography is seen in this World War II adventure story based on the Operation Source attack on the German battleship Tirpitz in 1943.