Following its narrow escape from the huge underwater ice chunks, the Seaview surfaces to find that the sky is blazing hot and literally on fire. The three men who have climbed outside on top deck are so hot they have to climb back down into the sub to escape the heat. Two of the men re-enter the sub and are soaked in sweat, however Captain Crane has remained outside on deck and he is not sweating at all, even though he is still outside in the blazing heat.
The Admiral states that the minefield the sub encounters is too deep for divers, so they send out the minisub to cut the snagged cable. But earlier, during the effort to tap the telephone cable, they had used divers - even though, judging by the depth to which the Seaview had to dive (as depicted in the scenes of it sinking to the ocean floor), they were clearly far too deep for divers to operate.
During the effort to tap the underwater telephone cable, a crewman twice flashes a large flashlight to signal the sub. In the close-ups, the light as shown is very dim, barely lighting the bulb's filament and throwing no beam, but in the distance shots, it's casting a thick, highly visible beam.
After the ice scene at the beginning, the Captain orders the Seaview to the surface. The next shot we see is the Seaview with its dorsal fin above the water. After the admiral has put on his polar gear we are treated to a shot of the dorsal fin just breaking surface.
In most underwater scenes shot from within the nose of the sub, the water through which the sub is moving is calm. But in some underwater shots - diving to the ocean floor to tap the telephone cable, when they first learn they're being pursued by the UN sub - the water is foaming as the sub passes through it. Also, when the Admiral and Captain Crane go below to greet Dr. Hiller and the others at the beginning, the underwater view is perfectly still, showing no indication of movement, even though the sub is underway at the time.
Since space is a premium with submarines, there is not a submarine in the world that would have ten foot high ceilings inside the living quarters and operational spaces as shown.
In the film, and throughout the television series, whenever the submarine is compromised enough to allow water to leak through, there always seems to be a valve wheel nearby for the crew to turn and miraculously stop the leak. Any submarine who's structure is damaged enough to allow water to leak in cannot be repaired by turning valve wheels.
The sub is docked, yet a crash dive is ordered. A sub can't crash dive at a dock, it's too shallow. Crash dives can only happen in deep water.
Throughout the movie Cathy Connors wears high heels. That would never occur on any navy ship.
When the derelict yacht is spotted, Admiral Nelson says it "looks becalmed." A sailing ship is becalmed when there's no wind to move it. A motor vessel can be adrift, but it can't be becalmed.
During the tour at the beginning a keypad is shown with the numbers 1 through 10 on it. With no "zero" how could this keypad be used effectively?
Cathy Connors appears to be writing madly at the U.N. hearing, making some kind of scientific calculations, yet at one point she looks up and continues writing in what appears to be random scribbling.
During the supposed 'crash dive' at the dock, a TV screen appears to show the MPs who had tried to enter the boat to stop them, struggling to stay swimming on the surface. This is supposedly from a camera on top of the sub, maybe even in the periscope or on the mast, but although they are supposedly 'crash diving', the camera remains stationary in its view of the swimming MPs.
Near the end of the movie, Alvarez grabs what looks like a grenade off of a remarkably handy shelf. Doubtless aboard a regulation Naval vessel, such a weapon would not be casually laying around like that and would be stored in a munitions locker.
When the Seaview is escaping from the UN subs, Crane orders Battle Stations. When the torpedo hits the sea-mount, we see a large group of men in the mess hall, with dishes clattering, and breaking. At battle stations, no one would be calmly eating in the mess hall.
The ship's quarters are absurdly grand, and quite a lot of smoking is done, neither of which are appropriate for a submarine.
When the crew don their cold weather gear (which appear to be jackets) and exit the sub, they immediately take them off because of the heat. When they go below they do not bring the gear with them. They get under way with the jackets left outside.
The Seaview is a futuristic design far beyond the conventional submarine in technology and capability. Yet their scuba gear is entirely conventional, with no wireless communication, leaving them having to communicate by waving flashlights.
Near the start, when Admiral Nelson and Captain Crane go below to greet Dr. Hiller and the others, the underwater scene through the windows shows the sub very near if not on the surface. The captain ordered the sub to a depth of 90 feet just minutes before.
Lt. Connors and Dr. Hiller both scream in different scenes. The exact same scream is used for both.
The route that Seaview takes to get to N 15 E 143 is around Cape Horn and into the Pacific from the tip of South America. Such a route is approximately 17000 Nautical miles and Seaview would need to sustain a speed of advance of more than 45 knots in order to reach the firing point within the 16 day window. A much shorter route could be had by the Northern route through Baffin Bay in Canada and back through the North Polar region. This route is approximately 9700 NM, almost half the distance. By the time Seaview returned to the North Pole region, ice would no longer be a factor, having already melted from the heat.
According to the dialogue, the Seaview has been underway from New York for 25 hours when its location is put off Cape de Sao Roque, in Brazil - a distance of at least 3000 miles. It is not possible that the sub could have crossed that distance in so short a time (and if it could do so, it wouldn't take them 16 days to reach the Marianas from New York, as Admiral Nelson says he requires).
The Seaview is shown approaching Manhattan Island and the UN across a very broad, open expanse of water. The UN building is located on the East River, which is a very narrow body of water separating Manhattan from Long Island. The water is nowhere near as wide as depicted.
During the underwater search for the transcontinental telephone cable, the divers spend two minutes swimming at full speed away from the Seaview. During that time they go through a kelp forest, and an overhead rock formation, to get to the cable. Yet, when Captain Crane turns around and signals the sub that he's found it, his waving flashlight is only about 30 yards away from the sub, along a flat sea bottom.
Seaview has a big fish tank, full of water and open on top. What happens to the contents during a crash dive?
In the satellite view of the burning Van Allen belt shown in the TV broadcast, the belt is seen circling the Earth's equatorial and tropical belt regions only, but it is not seen surrounding any of the planet's middle and higher (polar) latitudes. How is it then that the "fire in the sky" is seen directly overhead in the Arctic? Additionally, the newscaster says the view is from satellites orbiting Earth. However, the view shown on the TV screen indicates the camera is very far outside Earth's orbit.
If the meteorological conditions prevented Seaview from any contact with its own Naval Command, there would be no method to contact the "UN Submarines" in order to position them for the ambush.
News reports of the Earth's gradual demise are played on the ship's intercom system for some time so all crew members can hear it. Only after the crew hear the bad news for a while does the admiral institute a news blackout to save crew morale. Waiting until after they hear it does no good, and no respectable boat captain would allow bad news to be played.
When the derelict yacht is sighted, Captain Crane says "On the ship" over a bullhorn. A Navy career man would have said "Ship ahoy."
Dr. Hiller sabotages the nuclear reactor on the Seaview. But she is a civilian psychologist with no naval background. Therefore, she would have no idea of how to engage in such sabotage.
Admiral Nelson orders the submarine to submerge near the end of the movie and calls it a 'ship' (i.e. "take the ship down"), but all submariners call their submarines 'boats', not 'ships'.
On the scuba expedition to find the telephone cable, all of the divers are inexplicably swimming ahead of Crane, who has the metal detector. In fact they have no idea that he has found the cable, or is being attacked by the octopus, for 3 full minutes.
The Seaview has dived into the Marianas Trench to avoid another submarine's torpedoes. Once that danger has been avoided, Nelson decides it is time to fire the missiles and gives the order to standby to fire. Missiles would not be fired from the deepest place in the ocean, the Marianas Trench. Rather, they would be fired close to the surface. So, the Seaview would have to leave the Marianas Trench and approach the surface before Nelson would give such an order.