Continuity mistake: When the Japanese ship is about to be torpedoed, there are no numbers or letters on its side. In the next shot, when the ship explodes, a large white "265" is visible on the port side of the ship.
Continuity mistake: Sometimes when they are looking through the periscope, the sub view is going the opposite direction than the periscope view is.
Continuity mistake: When the sub is being strafed by the Japanese fighter, John Wayne is wounded as he enters the doorway with his back toward the fighter. Yet, when he is taken to his quarters, it is his chest that is wounded and his back is untouched.
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.
Continuity mistake: Towards the end, John Wayne says to run silent and dive deep, but the outside shots continually show them to only be about 25 feet above the bottom.
Continuity mistake: As Japanese planes strafe the U.S.S. Thunderfish, the insertion of a brief piece of sub-being-struck-by-gunfire stock footage changes the American submarine into a German U-boat. (01:30:00)
