Nuclear testing can alter the marine ecosystem, until frightful mutations are created. This is the premise of this film, which tells how a biologist inside a very small submarine discovers that the cause of the massacres of fishermen is a monstrous, bloodthirsty octopus.

"The monster, in truth, was a puppet viewed on a wide-angle screen. I did not have money to spend on effects like the transparent ... " (from the book "How I Made A Hundred Films in Hollywood Without Losing a Dollar" by Roger Corman and Jim Jerom).

The first film produced by Roger Corman that made this much money, was in 1953, selling subject of FBI Operation Las Vegas to Allied Artists. Initially titled "It Stalked the Ocean Floor", the story takes place on the Yucatan coast, but turned around in a week - to the vicinity of Malibu (California) and a house rented for a single day.

Contributing to the success of the film and to help its distribution and the publicity was also the submersible Aerojet General single-seat electrical submarine thatit turned out was lent to Corman by the manufacturer.