Factual error: As the movie opens, the submarine is dispatching frogmen to acquire Japanese mines that are sonar-proof. The problem with this is that in order to locate mines by sonar, either the mines must make noises to be picked up by passive hydrophones, or the submarine has to start pinging with active sonar. Doing this makes the submarine vulnerable to any enemy listening in. I can't imagine a submarine venturing into a mined strait, announcing to one and all, "Here I am"..
Factual error: WWII divers are seen using open-circuit SCUBA gear that was not available at that time.