20,000 Leagues Under the Sea Trailer (1954)

The trailer for 20,000 Leagues Under the Sea.

In the year 1868, rumors of a sea monster attacking ships in the Pacific Ocean have created apprehension and fear among sailors, disrupting the shipping lanes. Prof. Pierre M. Aronnax and his assistant, Conseil, are on their way to Saigon but get stuck in San Francisco by the halting of ships. The U.S. government invites Aronnax onto an expedition to either prove or disprove the monster's existence. One of their fellow crew is the cocky master harpooner Ned Land.

After months of searching, the monster strikes, ramming the naval frigate. Ned, Aronnax, and Conseil are thrown overboard, and watch in horror as their ship, badly disabled, is unable to rescue them. The three drift into a strange-looking metal vessel, and realize the "monster" is a man-made "submerging boat", that seems to have been deserted. Inside, Aronnax wanders down into the Salon, where he finds a massive viewing window and sees an underwater funeral taking place.

When the submarine crew returns to their ship, they capture the three castaways. The captain introduces himself as Nemo, master of the Nautilus. He returns Ned and Conseil to the deck, while Aronnax, whom he recognizes for his work and research, is allowed to stay. He tempts Aronnax to remain with him, but Aronnax prefers to share his companions' fate. Nemo prepares to submerge Nautilus with the three stowaways on the deck, but at the last moment changes his mind and allows them to stay. After dinner that night, Nemo takes them all on an underwater expedition to gather supplies, but Ned tries to salvage a treasure chest from a sunken wreck, almost getting attacked by a shark.

Later on, Nemo takes Aronnax to the penal colony island of Rura Penthe. Nemo reveals he was once a prisoner there himself, as were many of the crew of the Nautilus. A munitions ship embarks at sunset, whereupon the Nautilus rams it, destroying its munitions cargo and killing the entire crew. When confronted by Aronnax, Nemo claims that his actions have just saved thousands from death in war; he also discloses that this "hated nation" had killed his wife and son in an attempt to force him to reveal his atomic secrets. Meanwhile, Ned discovers the coordinates of Nemo's secret island base, Vulcania, and releases messages in bottles, hoping somebody will find them and free him from captivity.

Off the coast of New Guinea, the Nautilus gets stranded on a reef. Ned is surprised when Nemo freely allows him to go ashore with Conseil, ostensibly to collect specimens. Ned goes off alone inland to explore avenues of escape, until he sees a bunch of human skulls, and a cannibal in a tree. Realizing his danger, Ned runs for his life and rejoins Conseil as they are chased back to the Nautilus. Despite remaining aground, Nemo is unconcerned and the cannibals are repelled from the ship by electrical charges circulated on its hull. Captain Nemo is furious at Ned for not following his orders, and confines him to the submarine's brig as punishment. A warship approaches, firing and striking the submarine just as it breaks free of the reef. It descends into the depths, where it attracts the attentions of a giant squid. The electric charge fails to repel the monster, so Nemo and his men are forced to surface in order to fight and dislodge the beast. During the battle, Nemo is caught in one of the squid's tentacles; Ned, having escaped from captivity in the struggle, jumps to Nemo's rescue and saves his captor's life. As a result, Nemo has a change of heart; he claims now to want to make peace with the outer world, by sharing his secrets of the sea. However, this is to be short-lived.

As the Nautilus nears Vulcania, Nemo finds the island surrounded by warships, whose marines are converging on his hideout. He goes ashore, setting a time bomb to destroy his discoveries, but when returning to the Nautilus, he is struck in the back by enemy fire and mortally wounded. After navigating the submarine away from Vulcania, Nemo announces he is "taking the Nautilus down for the last time." Loyal to Nemo to the very end, his entire crew declare that they will accompany their captain in death.

Aronnax, Conseil, and Ned are taken forcibly to their cabins. Ned fights back, escapes to the now deserted bridge, and manages to surface the Nautilus, hitting a reef in the process and causing the ship to begin flooding rapidly. In his final moments, Nemo staggers to a viewing window, collapses, and looks at his beloved ocean one last time as he dies.

Aronnax tries to go back and retrieve his journal, which contains an account of the voyage, but the urgency of their escape obliges Ned to knock him unconscious and carry him out. The companions witness Vulcania destroyed in a explosion. The shock from the explosion causes the Nautilus to sink even more quickly, and as it disappears beneath the waves forever, Nemo's last words to Aronnax echo: "There is hope for the future. And when the world is ready for a new and better life, all this will someday come to pass. In God's good time." Aronnax's diary of the voyage is also lost forever, and when Ned apologizes for having hit him, the Professor replies "Perhaps you did mankind a service, Ned".