VOYAGE TO THE BOTTOM OF THE SEA (1961). The original movie, not the tv show. Seems a meteor shower messed-up the Van Allen radiation belt, and the Earth is starting to cook. Soon we'll all be dead. It's up to Walter Pidgeon and Peter Lorre to figure this mess out, from inside a state-o-the-art atomic submarine, with a crew that includes Joan Fontaine, a scrumptious pre-Genie Barbara Eden, and Frankie Avalon (?)--all of whom chain smoke throughout the entire flick. I guess if they launch a nuclear bomb from the depths of the ocean it'll solve everything (?), so that's where they go, despite the UN forbidding them to do so. A couple of saboteurs try jinxing the whole set-up, one of whom being the aforementioned Ms. Fontaine, who dies by falling into the submarine's shark tank; why they had a narrow walk-way crossing this open shark tank (or why they even HAD a shark tank) I never figured-out. Do our heroes succeed, or do we all die a fiery death? Sorry folks, no spoilers here (eeeeps!).
(Oh, I forgot to mention the giant Squid attack.)