During World War II, the American submarine ''Thunderfish'', under the command of CDR John T. "Pop" Perry, takes charge of a group of nuns and children, including a newborn infant nicknamed "Butch", transporting them to Pearl Harbor. On their way, the sub sights a Japanese aircraft carrier and attacks, but its torpedoes malfunction, exploding halfway to the target. Pursued by the carrier's escort destroyers, ''Thunderfish'' manages to escape.