Other mistake: In the battle for Fredricksburg you can see streaks in the sky from jets.
Other mistake: When the home guard are trying to force the Swanger boys out of hiding by crushing Sally Swanger's fingers in the fence, it appears to be only her fingertips that they've trapped. Yet when Ruby and Ada come to help her (a couple of scenes later), as they pull the fence up, the majority of her fingers come out from the fence.
Other mistake: The Gatling guns used in the final battle scene are indiscriminate weapons. We see the warriors hit multiple times with spectacular entry and exit wounds, as well as rounds impacting with the ground leaving dust clouds. But the horses seem to be spared as if by an invisible shield.
Other mistake: If the scene in which Jack Aubrey gives the order "hard a larboard" [meaning the opposite of starboard] was indeed a rudder order (ie. turn the rudder in the direction commanded, which turns the ship the other way, in this case to starboard) the face of the compass wouldn't have rotated clockwise. The compass shows a southerly course, rotates clockwise, and eases to show an easterly course, which is a 90 degree turn to port.