After their ship is sunk in the Atlantic by Germans, eight people are stranded in a lifeboat. Amongst the survivors is a glamorous journalist, a tough seaman, a nurse and an injured sailor. Their problems are complicated further when they pick up a ninth passenger - the Nazi captain from the U-boat that torpedoed them.

Welcome aboard the Seaview, "the most extraordinary submarine in all the Seven Seas!" From the outside, the ship appears to be a high-tech research vessel, but it's actually the mightiest weapon in the Cold War arsenal of the U.S., sent on perilous, top-secret missions to battle the enemies of mankind.