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.
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.
Other mistake: The first shot of the torpedo impact on the rocks is reused the second time for the torpedo impact.
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