An area of the submarine that is restricted has a "Restricted Area" sign on the inside of the compartment door rather than on the outside where it could be read by people trying to enter.
At the beginning Capt. Crane says, "I don't see how anyone could be hiding within a radius of 50 square miles." This makes no sense. He presumably was supposed to say something like, "a radius of 50 miles," or, "an area of 50 square miles."