Revealing mistake: When the torpedo is fired at a Japanese ship, the underwater shot of the torpedo cruising reveals it being pulled by a long wire. It is also apparent that it was filmed in a tank with the reflection of the sun on the tank wall.
Revealing mistake: In this scene we see John Wayne talking to the deck gunner who is manning his post. There are also some sailors who are scanning the horizon for enemy shipping. It is obvious the background scenery of a cloudy night is a stage prop. You can also see a dark line coming down, meaning it was put together in panels. The fact that the clouds don't move or change shape also suggests the use of a stage prop. (01:14:20)
Factual error: The Thunderfish is closing on the Japanese I-boat, at under 6000 yards, Duke orders flank speed. The hydrophone operator on the I-boat would have to be deaf not to pick up the noise of Thunderfish's propellers at flank speed. For those pundits who claim that their sonar might be down, hydrophones are a passive listening system.
Continuity mistake: When Thunderfish engages the Japanese I-boat, the first range and bearing indicates that the sub is some 6000 yards distant. Less than a minute later, the range has dropped to 900 yards. That would mean that even if both vessels were on directly opposite courses, their combined closing speed would have to be in excess of 250 nautical miles per hour, impossibly.