Ameriška mornarica v bližini Havajev prireja mednarodno vojaško vajo, ko v Pacifiku pristanejo neznani leteči predmeti. Nezemljani so sledili signalom z Zemlje in želijo zavzeti naš planet, invazijo pa lahko preprečijo zgolj tri ladje, ki se znajdejo v bližini uničevalnih vesoljskih strojev. Po prvem porazu s številnimi žrtvami mora poveljstvo prevzeti vročekrvni stotnik Hopper in pred vnovičnim spopadom zgladiti spor z japonskim kapitanom. Skupaj skušata odkriti način, kako v divjih spopadih na morju poraziti sovražnikove ladje in uničujoče robote.

Maverick Navy Lieutenant Commander Tom Dodge will never be a textbook officer, but he's a brilliant seaman who's always wanted to command a nuclear submarine — he's been given one last chance to clean up his record. Unfortunately, Admiral Graham, his nemesis, would rather sink the fleet than give Dodge his own boat. So, Graham stacks the deck against him and assigns Dodge to the Stingray, a diesel-powered WW2 submarine that can barely keep afloat. To make matters worse, Dodge's crew is a collection of maladjusted, mistake-prone misfits. Then, he's tagged the "enemy" in a crucial war game, and ordered to take on the U.S. Navy's best.

Merchant Marine sailors Joe Rossi (Humphrey Bogart) and Steve Jarvis (Raymond Massey) are charged with getting a supply vessel to Russian allies as part of a sea convoy. When the group of ships comes under attack from a German U-boat, Rossi and Jarvis navigate through dangerous waters to evade Nazi naval forces. Though their mission across the Atlantic is extremely treacherous, they are motivated by the opportunity to strike back at the Germans, who sank one of their earlier ships.

This film shows the duties of a young British sailor, Lieutenant Ellison, as his submarine H.M. Artemis sails the pack ice north of Iceland to gather data to complete a scientific survey for the Hydrographic Department.