"For centuries the mind of man has learned comparative little of the mysteries of the heavens above - or the seas below"
"Since the coming of the atomic age, man's knowledge has so increased that an upheaval of nature would not be beyond his belief."
It is 1955 and the atom sub looks just like a ww2 diesel (at least it does not look like a cardboard mockup.) The latest sub is being chased by thing or things unknown; let's just say that "It Came from Beneath the Sea".
Standard sci-fi for the time we have the obligatory romance between the captain, Cmdr. Pete Mathews (Kenneth Tobey) from "The Thing From Another World" (1951), and Prof. Lesleyl Joyce (Faith Domergue) from "This Island Earth" (1955). What a ménage à trios and Prof. John Carter (Donald Curtis) from several "Science Fiction Theater" (1955-1957) TV episodes.
I just love sci-fi from this time because they inevitably depend of flame throwers to do the trick as in "The deadly Mantis" and "Them!"
Naturally no one believes them until they get eaten. Others think they have the situation in hand. Will we be able to handle "IT"? And will there be a next time?
Six tentacle monster by Ray Harryhausen; "Clash of the Titans" (1981). Screen play by Hal Smith, and George Worthing Yates. Faith Domergue, by God.