In 1943, a British naval officer from Canada, Commander Bolton (James Caan) and a few surviving crew members of his 50-man submarine ''Gauntlet'' swim ashore after unsuccessfully attacking German battleship ''Lindendorf''. After a review, Captain Bolton is cleared of any wrongdoing and placed in charge of a small group of experimental X class submarines. Bolton is assigned by Vice-Admiral Redmayne (Rupert Davies) to quickly train crews to man the submarines and sink the ''Lindendorf'' while it is hidden away in a Norway fiord.