Factual error: When Rock is shaving, and then when he goes to Eddington's cabin, both cabins and the passageway have fluorescent lights. Since this type of lighting wasn't commercially available until earlier in 1941, it is unlikely that an elderly heavy cruiser like "Swayback" would have been equipped with such modern lighting.
Other mistake: After the sub attack, Mac informs Rock that he graduated from the Naval Academy in 1939. That would make him around 25 in 1941. The actor playing Mac was nearly 40. No competent officer would still be a Lt. JG at that age.
Continuity mistake: After USS Cassidy joins Torrey's group, Mac is on the bridge conversing with another officer, and the "Swayback" is visible on the port quarter. A submarine contact is made at 020/2000 yards which would be even further to starboard, and the Cassidy prosecutes the contact. Then the "Swayback" gets hit with two torpedoes on the PORT side.
Factual error: During the attack on Pearl Harbor, the destroyer Cassidy's aft 5-inch guns are moving, but they never fire.
Factual error: Not one Navy uniform has the placement of Officer's rank insignia on the collar correct, especially the single bar for Ensigns and JGs. They are all too far up. Insignia are not centered in the collar point, but placed about a thumb's width distance from the point.
Revealing mistake: During the attack on Pearl Harbor, we see a sailor cut the stern line so the destroyer can get underway. But the bow line is still attached as the ship is supposedly moving off.
Factual error: When Kirk Douglas is at the morgue to identify his wife's body, he asks the attendant about the man she was brought in with. The attendant replies, "The Army Air Force claimed the body this morning." Unlike Britain, the United States had no Air Force until 1947. A correct reply would have been "The Army..." or "The Army Air Corps..."
Answer: One Star rank wasn't formalized until 1943. Rear Admiral lower and upper wore the same 2-stars.