Because the budget was so low, Ray Harryhausen saved money by building his octopus model with six rather than the correct eight tentacles. He tried to pose the creature so this lack of the right number of arms wasn't apparent.
Columbia booked this as a double bill with Creature with the Atom Brain all across the US.
The "atom-powered" submarine shown cruising on the surface is actually the diesel-electric submarine USS Cubera (SS-347).
The Special Jet Propelled Torpedo is actually a aerial torpedo (it was delivered by aircraft and by torpedo boats) that had it's propellers and rudders removed.
This is the film that brought together producer Charles H. Schneer and special effects legend Ray Harryhausen. Their professional relationship would last until Clash of the Titans, the final feature for both men.