Factual error: When the sub is being pelted by huge chunks of ice (which should float, not sink, as mentioned earlier), the sub is not knocked off course or damaged in any way. (00:20:00)
Factual error: With the radiation belt on fire, the icecaps begin to melt. The Seaview is bombarded by huge chucks of ice. The ice is sinking to the bottom like stones. Ice floats, it doesn't sink.
Revealing mistake: During the initial dive the hydroplane on the sail (conning tower) is pointing upwards. During a later dive the hydroplane is pointing downwards. Wouldn't one position cause the submarine to surface?
Factual error: The "Colours" were not flown whilst the Seaview was docked in New York harbour.
Factual error: After leaving the New York conference and hurriedly returning to the Seaview, they didn't ask permission to come aboard.
Other mistake: When they are in the trench the other sub fires two torpedoes at them. The captain calls for right full rudder. They then show an underwater show of the sub turning left. After two more torpedoes are fired the captain orders left full rudder and they show the same underwater shot of the sub turning left.
Revealing mistake: Captain Crane to thwart the bad guy has to exit the sub using scuba gear and make his way to a missile silo and attach a magnetic primer to the missile to fire it. Just before he uses the exit a crewman attaches the primer to his belt on the right hand side. As he is pulling himself along by the handholds on the deck the primer is no longer on that side. As he arrives at the silo the primer appears in his left hand.
Revealing mistake: The submarine Seaview is pursued down the Marianas Trench by a United Nations submarine trying to destroy it. Seaview's sonar operator reports torpedoes approaching port side even though the pursuing sub is directly astern of and always has been astern of the Seaview.
Continuity mistake: After the fire in the captain's quarters everyone goes on deck for some fresh air. When they finally go below everyone has sweat soaked shirts except the psych doc who is perfectly dry.
Continuity mistake: About 30 minutes in, the sub surfaces to check why the ice has been hitting them. After they get outside the admiral starts to remove his parka. He pulls it off his arms and in a later shot he's pulling it off his arms again.
Plot hole: Whilst on the surface a drifting ship is seen and an officer and two sailors are sent to check it. On deck the officer says check fore and aft. The sailor who goes to the right and out of sight is back in 5 seconds. This is not enough time to check his allocated section. The script should have shown the officer check his watch (dial visible) and say something like "you have got 15 minutes". Next shot to show the officer checking his watch again and we see 10 minutes have passed and the men return.
Other mistake: About 11 minutes in the congressman steps on a pad in front of the reactor door and sets off an alarm. He backs off but his left foot is still half way on the pad and his right foot toe is on it but it doesn't go off. He walks away and the older guy put his toe on the pad and it goes off.
Continuity mistake: After the officers check out the burning sky, they start to below. Their shirts are perfectly dry but when they reach the bottom of the ladder inside they are all soaked.
Plot hole: The Seaview gets a mine cable snagged on its searchlight housing. Admiral Nelson says they are too deep for frogmen, use the mini-sub. As the two crew are entering they are seen to be wearing full scuba gear (less flippers).This suggests the mini-sub is not watertight and the above remarks by Admiral Nelson would apply to them also.
Continuity mistake: While Captain Crane is at the map station, they show him drawing on the map, but his hands are Barbara Eden's hands as they are female, and wearing a bracelet belonging to her in the movie.
Continuity mistake: A saboteur sets Admiral Nelson's quarters on fire. In the first shot from the corridor, looking through the doorway, we see his cabin is filled with heavy smoke. As crewmen arrive with fire extinguishers, the camera cuts to the interior of Nelson's cabin, where there is virtually no smoke, even though there are added flame effects in the foreground. Camera cuts back to the corridor, and heavy smoke is again pouring out of Nelson's cabin.
Other mistake: The first shot of the torpedo impact on the rocks is reused the second time for the torpedo impact.
Audio problem: As Nelson gives the order to dive after the crewmen leave the sub, the dive klaxon sounds, but nobody hit the button.
Continuity mistake: As Nelson begins to agree with Alvarez, his arms are crossed holding the Hawaiian newspaper. A second later, they're by his sides with the paper in his right hand.
Other mistake: Lee orders "All back, dead slow", meaning the sub was in reverse. As he orders stop, the sub is moving forward towards the mines.
Answer: Admiral Nelson is puffing on cigars in a few scenes, and his cigars are even a source of dialogue in the film. Specifically, when his quarters catch on fire, the blaze is initially blamed on a lit cigar, to which Nelson angrily replies that he ran out of cigars before the fire ever occurred. So it's a pretty good bet that Nelson was carrying a cigar (or cigars) in his shirt pocket.
Charles Austin Miller