Just after the opening scene, a camera pans a naval shipyard. One vessel (#54) is shown moored along side another at a dock. The same ship is then immediately shown in the open water of the harbor.
When O'Neill is given his mission at the start of the movie, he is wearing aviator wings instead of a submariner's "dolphins" qualification badge above his ribbons. When O'Neill reports aboard the sub, he's wearing the dolphins, but on his shirt pocket flap instead of where they belong, above the same pocket.
The navy officers are shown wearing their name-tags on their shirts' pocket flaps. They are worn a quarter of an inch above them.
The deeper in the ocean you go, the colder it is. All they had to do was dive down and turn off the heaters. As snakes are cold blooded they would have slowed way down and been easy to capture or kill.