Voyage to the Bottom of the Sea
Tags: insanity, claustrophobic

Plot synopsis:
The new, state of the art nuclear submarine Seaview is on diving trials in the Arctic Ocean. The Seaview is designed and built by scientist and engineering genius Admiral Harriman Nelson (USN-Ret) (Walter Pidgeon). Captain Lee Crane (Robert Sterling) is the Seaview's Commanding Officer. One of the on-board observers is Dr. Susan Hiller (Joan Fontaine), studying crew-related stress. The mission includes being out of radio contact for 96 hours while under the Arctic ice cap, but the ice begins to crack and melt, with boulder-size pieces crashing into the ocean around the submarine. Surfacing, they discover fire burning in the sky. After the rescue of scientist Miguel Alvarez (Michael Ansara) and his dog at Ice Floe Delta, the sub receives radio contact from Mission Director Inspector Bergan at the Bureau of Marine Exploration. He advises that a meteor shower pierced the Van Allen radiation belt causing it to catch fire, resulting in a world-threatening increase in heat all across the Earth. Nelson's on-board friend and scientist, retired Commodore Lucius Emery (Peter Lorre) concurs that it is possible. Bergan informs Nelson that the President wants him at a UN Emergency Scientific Meeting as soon as possible.
Nelson and Commodore Emery calculate a plan to end the catastrophe. The USOS Seaview arrives in New York Harbor in two days. At the meeting Nelson informs the UN that according to their calculations, if the heat increase is not stopped, it will become irreversible and Earth has "a life expectancy of about three weeks." The Admiral and the Commander have come up with a plan to extinguish the Skyfire. He proposes firing a nuclear missile at the burning belt from the best calculated location, the Marianas. Nelson posits that when fired at the right place and time, 1600 hours on August 29, the nuclear explosion should overwhelm and extinguish the flames, away into space, essentially "amputating" the belt from the Earth. The Seaview has the capability to fire the missile.
However, the Admiral's plan is rejected by the chief scientist and head delegate, Emilio Zucco (Henry Daniell) of Vienna. His reasons are that he knows the composition of gases in the belt and he believes the Skyfire will burn itself out at 173 degrees. Zucco's plan is to let the Skyfire do just that and he feels the Admiral's plan is too risky. Nelson claims that Zucco's burn-out point, however, is beyond that date and time if the current rise rate is maintained. But at Zucco's urging, Nelson and Emery are shouted down and the plan is rejected. Despite the rejection, the Admiral and the Commodore quickly leave the proceedings, advising that his only authorization will be from the President himself.
It is a race against the clock as the Seaview speeds to reach the proper firing position, above the trench in the Marianas in the Pacific. During this time Nelson and Crane agree on tapping the Rio-to-London telephone cable to try to eventually reach the President. However, an unsuccessful attempt on the Admiral's life makes it clear that there is a saboteur on board. But the confusion over who the saboteur might be revolves around rescued scientist Miguel Alvarez, who has become a religious zealot regarding the catastrophe, and Dr. Hiller, who secretly admires Dr Zucco's plan. Other obstacles present themselves: a minefield and a near-mutiny. And Crane himself begins to doubt the Admiral's tactics and reasoning. During the telephone cable attempt, Crane and Alvarez battle a giant squid. Although the London cable connection is made, Nelson is told there's been no contact with the States for 35 hours. Also, a hostile submarine follows the Seaview deep into the Mariana Trench, but implodes before it can destroy the Seaview.
Near the end of the film the saboteur is revealed to be Dr. Hiller. Captain Crane happens by as she exits the ship's "Off Limits" Nuclear Reactor core, looking rather ill. She has been exposed to a fatal dose of radiation: her detector badge is deep red. Walking over the submarine's shark tank, she falls in during a struggle with the Captain, and is killed by a shark. The Admiral learns that temperatures are rising faster than expected. He realizes that Zucco's belief that the Skyfire will burn itself out is in error.
At the end, Seaview reaches the Marianas. There, in spite of the threats and objections of Alvarez, Seaview launches a missile toward the belt and it explodes the burning flames outward, saving the world.