Character mistake: In the scenes in San Diego, all the scenes outside the sub are taking place during daylight hours. Immediately after the crewman relays the message about the mysterious telegraph transmission, the scene shifts to the sub. The commander asks what time it is in Melbourne and is told it is 1500 hours (3PM). But if it were that time in Melbourne, it would be 10PM in San Diego, and thus not during daylight hours.
Other mistake: According to the plot, no life is possible in the Northern Hemisphere by the time the film is set. Yet, when the sailor who has been sent ashore to look around the San Diego refinery enters the premises (more precisely, when we see the smoking-prohibited sign on our right and his left) a bird can be seen flying in the upper left-hand corner of the screen.