THUNDERBALL,
While it crosses into "Be really scared of Sharks" territory. How cool did scuba diving seem to you as a kid seeing this. I mean I totally wanted that Jet Propulsion Device that Sean Connery had strapped to his tanks. And that Pen-Sized Aqualung was pretty cool. And the Finale when hundreds of Divers Battle with scooters, etc.
I always wanted that Orange Shorty Suit he had as well.
20,000 Leagues Under The Sea (Kirk Douglas, James Mason)
It's funny as a Kid you see Nemo as Evil and an enemy of the State but as you get older you really appreciate his point of view that Mankind is cruel and warlike and only in the sea can one find peace...except for giant squids.
Also loved those Giant Shell Aqualung and Mask combos...