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. (01:33:30 - 01:38:05)
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.
Continuity mistake: In the part when the two American officers are looking around in Anchorage, USA, and come across the dead woman at the News Studios you can clearly see her blink 2 or 3 times as the camera pans out.
Trivia: When Moira and Bill Davidson are strolling in the pasture, they pause to admire a beautiful mare that is posing for them, and Bill offers the horse something to eat from the palm of his hand (sugar cubes or some other treat, presumably, but it's not visible). However, the horse does not react to the treat nor eat anything that Bill offers, because the actor's hand was actually empty. The trained horse was obeying cues from her trainer, off-camera, and only her trainer carried the real treats.Charles Austin Miller