Factual error: Many of the Royal Navy details are completely wrong. The submarine captain's cap badge is not that of the Royal Navy. "Midshipman" Leonard wears the insignia of a chief petty officer. "Officer" (not a naval rank) Neal wears the insignia of a petty officer. "Officer" Shaw wears the insignia of an able rating. The Flag Office Submarines is depicted as a full admiral, whereas in fact he was a rear-admiral and the position no longer exists.