The story is told from the viewpoint of Lt. Werner (Herbert Grönemeyer), who has been assigned as a war correspondent on the German submarine U-96 in October 1941. He meets its captain (Jürgen Prochnow), chief engineer (Klaus Wennemann), and the crew in a French nightclub. Thomsen (Otto Sander), another captain, gives a crude drunken speech to celebrate his Ritterkreuz award, in which he openly mocks not only Winston Churchill but implicitly Adolf Hitler as well.
Two children, Jacques Mayol (Jean-Marc Barr) and Enzo Molinari (Jean Reno), have grown up on the Greek island of Amorgos in the 1960s. They challenge each other to collect a coin on the sea floor and Jacques loses. Later Jacques' father — who harvests shellfish from the seabed using a pump-supplied air hose and helmet — goes diving for shellfish. His breathing apparatus and rope gets caught and punctured by rocks on the reef and weighed down by water, he drowns. Jacques and Enzo can do nothing but watch in horror as he is killed.
In 1984, Soviet submarine Captain First Rank Marko Ramius (Connery) commands Red October, a new Typhoon-class nuclear sub featuring a caterpillar drive, rendering it undetectable to passive sonar. Ramius leaves port on orders to conduct exercises with the V.K. Konovalov, commanded by his former student Captain Tupolev (Skarsgård). Once at sea, Ramius kills political officer Ivan Putin (Firth), and commands the crew to head toward America's east coast to conduct missile drills.
In 1988 a US ballistic missile submarine, the USS Montana, sinks near the edge of the Cayman Trough after an accidental encounter with an unidentified submerged object. As Soviet ships and submarines head toward the area in an attempt to salvage the sub, and with a hurricane moving in, the Americans decide that the quickest way to mount a rescue is to insert a SEAL team onto the Deep Core, a privately owned, experimental underwater oil drilling platform, located 1,700 feet (518 meters) below sea level, which will serve as their base of operations. The designer of the platform, Dr. Lindsey Brigman, insists on accompanying the SEAL team, even though her estranged husband, Virgil "Bud" Brigman, is currently serving as the platform's foreman.
The American Buckley-class destroyer escort USS Haynes detects and attacks a German U-boat that is on its way to rendezvous with a German merchant raider in the South Atlantic Ocean. Captain Murrell (Robert Mitchum), a former officer in the merchant marine now an active duty lieutenant commander in the Naval Reserve, has recently taken command of the Haynes, even though he is still recovering from injuries incurred in the sinking of his previous ship. Before the U-boat is first spotted, one sailor questions the new captain's fitness and ability. However, as the battle begins, Murrell shows himself to be a match for wily U-boat Kapitän von Stolberg (Curt Jürgens) (portrayed as not being enamoured with the Nazi regime) in a prolonged and deadly battle of wits that tests both men and their crews. Each man grows to respect his opponent.
In post-Soviet Russia, civil war erupts as a result of armed conflict in Chechnya. Military units, loyal to Russian ultra-nationalist Vladimir Radchenko, have taken control of a nuclear missile installation and are threatening nuclear war if either the American or Russian governments attempt to confront him.
The World War II U.S. Navy submarine commander P.J. Richardson (Clark Gable) has an obsession with a Japanese destroyer that has sunk three boats in the Bungo Straits, including his previous command. He persuades the Navy Board to give him a new submarine command with the provision that his executive officer, also known as the XO or the "exec", be someone who has just returned from active sea patrol. He single-mindedly trains the crew of his new boat, the USS Nerka, to return to the Bungo Straits and sink the destroyer, captained by a crafty ex-submariner nicknamed Bungo Pete. Richardson's executive officer, Lieutenant Jim Bledsoe (Burt Lancaster), is worried about the safety of his boat and his crew. Bledsoe is also seething with resentment at Richardson and the Navy leadership for denying him command of the Nerka, which he believes should have been his.
The American destroyer USS Bedford (DLG-113) detects a Soviet submarine in the GIUK gap near the Greenland coast. (Specifically, they are in Greenland territorial waters at the entrance to the J.C. Jacobsen Fjord, which is due northwest from Iceland.) Although the U.S. and the U.S.S.R. are not at war, Captain Eric Finlander (Richard Widmark) harries his prey mercilessly, while civilian photojournalist Ben Munceford (Sidney Poitier) and NATO naval advisor, Commodore (and ex-World War II U-boat captain) Wolfgang Schrepke (Eric Portman), look on with mounting alarm.
In 1959, United States Navy Rear Admiral Matt Sherman (Cary Grant), ComSubPac, boards the obsolete submarine USS Sea Tiger prior to her departure for the scrapyard. The first commanding officer of the Sea Tiger, Sherman begins reading his wartime personal logbook and recalling earlier events
In 1868, rumors of a sea monster attacking ships in the Pacific Ocean have created apprehension and fear among sailors, disrupting shipping lanes. The United States government invites Professor Pierre M. Aronnax (Paul Lukas) and his assistant, Conseil (Peter Lorre), onto an expedition to prove or disprove the monster's existence. On board with them is the cocky master harpooner Ned Land (Kirk Douglas).
On Christmas Eve, the submarine USS Copperfin, under the command of Captain Cassidy (Cary Grant), departs San Francisco on a secret mission. At sea, Cassidy opens his sealed orders, which direct him to proceed first to the Aleutian Islands to pick up meteorologist Raymond (John Ridgely), then to Tokyo Bay to obtain vital weather intelligence for the upcoming Doolittle Raid.
During 1964, in the months following World War III, the conflict has devastated the northern hemisphere, polluting the atmosphere with nuclear fallout, killing all life there. Air currents are slowly carrying the fallout south; the only areas still habitable are in the far reaches of the southern hemisphere.
British and Soviet ballistic-missile submarines mysteriously disappear. James Bond—MI6 agent 007—is summoned to investigate. On the way he escapes an ambush by Soviet agents in Austria, killing one during a downhill ski chase, and escaping via a Union Flag parachute. Bond learns that the plans for a highly advanced submarine tracking system are on the market in Egypt. There, he encounters Major Anya Amasova—KGB agent Triple X—his rival for the plans. They travel across Egypt together, tracking the microfilm plans, meeting Jaws—a tall assassin with steel teeth—along the way. Bond and Amasova later team up through a truce agreed by their respective superiors and identify the person responsible for the thefts as the shipping tycoon, scientist, and anarchist Karl Stromberg.
Three very likeable losers fail while they pursue individual goals. Roland Darbont (Lino Ventura) is an inventor who has designed his own engine. Manu Borelli (Alain Delon) on the other hand is a pilot who prepares a spectacular stunt. Both of them are running tests on Darbont's premises when they are joined by Laetitia Weiss (Joanna Shimkus), an artist who builds abstract statues from scrap metal. They nourish each other's hopes and learn to get along with each other.
A Russian submarine called Спрут ("Octopus") draws too close to the New England coast one morning when its captain (Theodore Bikel) wants to take a good look at America and runs aground on a sandbar near the fictional Gloucester Island, which, from other references in the movie, is located off the coast of Cape Ann or Cape Cod, Massachusetts. Rather than radio for help and risk an embarrassing international incident, the captain sends a nine-man landing party, headed by his zampolit (Political Officer) Lieutenant Yuri Rozanov (Alan Arkin), to find a motor launch to help free the submarine from the bar. The men arrive at the house of Walt Whittaker (Carl Reiner), a vacationing playwright from New York City. Whittaker is eager to get his wife Elspeth (Eva Marie Saint) and two children, obnoxious but precocious nine and half-year-old Pete (Sheldon Collins) and three-year-old Annie (Cindy Putnam), off the island now that summer is over.