**SPOILERS** Leaving it's port of call, the US Navel base at Bangor Maine, and sailing out to the Pacific the US Nuclear Submarine USS Lansing is some ten miles off the coast of North Korea. It's then that the Communnist Koreans detonated a nuclear device short-circuiting it's electronic and communication equipment, as well as knocking out power in all the surrounding countries, leaving the ship totally in the dark to what's happening in the outside world.
The Lansing's commander young Capt. Miles Sheffield, Casper Van Dien,tries to get in contact with the Pacific Fleet commander Admiral Eugene Justice, Gerald MacRaney, headquartered at Pearl Harbor but all communications are dead. This leads the second in command of the ship Lt. Com. Albert Kenner, Stewart Bick, to feel that the US is under attack. Kenner wants Capt. Sheffield to launch the Lansing's four nuclear-tipped Tomahawk missiles at either Communist China or the new Russian government in the former Soviet Union, whom he feels are at war with the United States.
We've seen earlier in the movie that there's trouble brewing between the crew over the fact that Capt. Sheffield was put in command of the Lansing over Capt. Kenner who's more respected by many of those on board due to his much more experience in the underwater, or silent, service. With a total black-out to what's happening in the world above Capt. Sheffield tells the concerned, and almost hysterical, let. Com. Kenner that he'll have the Lansing surface to show him that everything on shore is all right and not to worry.
Breaking on the surface outside the South Korean seaport of Ulsan it turns out that there's no sign of life at all with the entire town pitch black, this due to a power black-out not a nuclear attack like Let. Com. Kenner feels happened. Later when returning below it's discovered that both Sheffield & Kenner were contaminated by fall-out, from the North Korean nuclear blast.
Kenner and his followers on the sub, seeing their chance, forcibly takes command of the Lansing from Capt.Sheffield who was suffering from a far more serious radioactive dose, as was not given the proper medication, that Kenner was. The new commander Capt. Kenner quickly has the four nuclear-tipped Thmahawk missiles armed and ready to be launched at cities in both China and Russia in retaliation for, what he thinks was, their attack on the US. With no way of getting in touch with the Lansing, and it acting erratically at sea, Admerial Justice reluctantly comes to the realization that it's in danger of igniting a world war. Admerial Justice sends out the US attack Submerine USS Mako to first communicate with the Lansing to stop it's unstable and dangerous actions or, if that doesn't work, sink it before it does.
Exciting and heart-stopping ending with Capt. Sheffield and his crewmen retaking control of the sub and at the same time being tracked by the attack-sub Mako that's trying to sink it not knowing that Capt. Sheffield had the Tomahawks disarmed and stopped from being launched. Using evasive Maneuvers the Lansing Sails underwater through the very dangerous "Tin Can Alley", aptly named for the scores of sunken ships left there from the Russo-Japanese War, outside the Russian port-city of Vladivotok.
The Lansing makes it to safety in Russian waters as the Mako withdraws from the chase not attempting to navigate through the hazardous ship graveyard. Surfacing the crew of the Lansing found out that there was indeed life in the city and that no world war broke out above sea and at the same time they didn't, unknowingly and tragically, start a world war from down below.
