Continuity mistake: When Nelson comes into the control center, the report is that the sub was just breaking the surface. However, the prior shot of the sub travelling along showed that it was already at the surface, with the conning tower above the waterline.
Continuity mistake: In the opening, the TV newsman has holds the pencil eraser end down next to the paper he's reading from. When the angle changes the pencil is now eraser end up.
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