The film takes place primarily in the waters off the coast of North Korea with some scenes set in Hawaii. As it opens, an American submarine under the command of Commander Habley is attacked by an enemy submarine that has no sonar signature. Although it survives the fight, the American submarine is badly damaged and Tom, Habley's Executive Officer and lover, is killed.
The film begins in November 20, 1969, 50 miles off Soviet waters. When the USS Acushnet dives under the ice, a young Ahab listens for enemy subs when suddenly he detects an unknown target. When the captain listens, he hears nothing, but Ahab insists in the presence of an emptiness. The target dives into a trench, but the captain abandons his search in favor of photographing the target. The target attacks the submarine as Ahab hears a roar. The sub is brought to the icy surface, and the target identifies itself as a gigantic, white, whale-like creature. Ahab survives, but loses his leg to the beast when it hauls the other half of the sub back underwater.
In the last months of the Second World War, the Empire of Japan receives a final gift from the collapsing Nazi Germany: the I-507, a highly advanced submarine equipped with experimental technology.
HMS Scorpion, a British submarine that had gone missing in the Baltic Sea during World War II, surfaces in the path of a Russian freighter in 1981. The vessel is returned to British custody. Naval Intelligence is interested in the case because it seems that, for the first time, a ship has returned from "the Devil's Triangle of the North". The submarine opens its own hatch to let the investigating team in, where they find the vessel in a state of perfect preservation, but find no sign of the crew.
In 1914 Vienna, Elsa Elsbergen volunteers for nursing, but her lies hiding her sordid past are discovered and she is turned down. However, Captain Muller believes her patriotism and background are perfect for the Austrian Department of Intelligence. His superior, Major Schmidt, wants her to become very friendly with Captain Otto von Lichstein, who is known to be spying for the enemy. Elsa is disappointed at the use that Schmidt wants to make of her, but accepts the assignment. At a party, she catches von Lichstein's eye and agrees to meet him the next night.
L’Orsa Maggiore est le nom d'une escadrille spéciale de la Marine italienne qui effectue des missions de sabotage pendant la Seconde Guerre mondiale. Les hommes grenouilles qui la composent utilisent des maiali, des torpilles pilotables. L'action à Gibraltar est leur première mission. Les hommes grenouilles posent des mines sur trois navires anglais qui sont coulés ; pendant l'action, un homme grenouille et une femme agent secret de support à terre sont tués.
The USS Charleston (SSN-704), a 688i variant Los Angeles-class submarine, is equipped with a caterpillar drive and is on station following a nuclear exchange, and is under the command of Captain Dwight Towers.
The US Navy nuclear-powered attack submarine USS Jimmy Carter is attacked by a mysterious underwater object that stalks and disables the Seawolf-class super-sub with a powerful electromagnetic pulse. The underwater Arctic research complex Hubris witnesses the attack and reports a rapid rise in the temperature of the Polaris Trench which threatens to melt the ice cap and flood the world's land surface. At an emergency United Nations scientific conference, Hubris director Dr. Ann Fletcher is dismissed when she urges caution and her archrival Dr. Chomsky pushes through a far more aggressive plan to deal with the crisis. When Chomsky's plan fails and contact with the Hubris complex is lost, Dr. Fletcher is asked to participate in a follow-up expedition, which also includes Chomsky, by her ex-husband, Navy Captain Andy Raines. Once at the North Pole, the expedition finds that the Hubris complex is completely intact, but its personnel have been incinerated.
Septembre 1942, au large de Cape Town, en Afrique du Sud. Le "RMS Laconia", qui vient de quitter le port, fait route vers l’Angleterre avec 2 000 passagers à son bord ainsi que 1 800 prisonniers italiens. Les fumées du navire sont bientôt repérées par un U-Boot. Sa taille laissant supposer qu’il peut transporter des troupes, la décision est prise de le torpiller. Cela fait, le sous-marin ne quitte pas immédiatement les lieux. Découvrant le sort des prisonniers italiens, mais aussi de civils, le capitaine, se référant à un code d’honneur maritime, ordonne l’organisation du sauvetage, arbore une croix rouge dans l’attente d’un bâtiment français envoyé par Vichy. Mille personnes seront sauvées. Peu après, ce sous-marin sera coulé par les forces alliées tandis que l’amiral allemand Dönitz signera le "Laconia order" interdisant à l’armée allemande de procéder au moindre sauvetage.
"Remember the Lusitania! Avenge the Lusitania!" These are the words that inspired many young US citizens to volunteer for service during the First World War. The sinking of this great British oceangoing liner provoked outrage around the world on an unprecedented scale. On May 7, 1915, a German torpedo sent the ship to the bottom of the North Atlantic Ocean in just 18 minutes—its speedy descent into the depths occurring far too fast for most of those aboard to make it to the lifeboats. Of the 1,962 passengers and crew on board, 1,200 were lost, including 94 children and, crucially, 128 US civilians, many of whom were prominent figures. President Woodrow Wilson's neutral stance started to crack. All over the country there were calls for the United States to take up arms against Germany. In many ways, the Lusitania tragedy was the major turning point of the Great War, and perhaps the single greatest factor that eventually brought the USA into the war in April 1917.
A tugboat pulling a huge iceberg arrives at a port in Alexandria, Egypt, when suddenly, the iceberg shatters and releases a megalodon from suspended animation. The Mega Shark begins its reign of terror by flipping the tugboat to the air until it crashes and decapitates the Sphinx hundreds of miles away in Giza. Following the incident, several countries around the world place their ports on lockdown and impose a ban on fishing, adversely affecting the world's economy as the megalodon terrorizes the seas. Meanwhile, rumors surface of the United Nations' proposal to develop a weapon to combat the shark.