The Enemy Below (1957) - 2 mistakes

Factual error: When the UBoat changes course, Andrews, operating the radar repeater, is immediately able to provide the bridge with the target's new course and speed. This would be impossible without extensive calculations and at least range and bearing plots once the target has steadied up on the new course, either figured on the scope screen or on a maneuvering board. One must remember that both vessels' courses and speeds must be taken into account when making computations, and the relative direction of a target's travel most often is not its true course.

Character mistake: When the U-Boat first appears on the U.S.S. Haynes' radar screen, operator Andrews turns his head to the screen a split-second before the blip actually appears. The swiftness of his reaction indicates that he is reacting to the radar signal, not that he has his face turned to the screen by chance; the actor simply made his move too early.