When the PT boat is rescuing survivors and they spot a U-boat, the young boy who was being hauled aboard the PT boat is wearing a life-jacket. The close up in the next shot shows Lt Stewart lifting the boy up to put him back in the lifeboat. The boy is no longer wearing the life-jacket. In the following shot, as Lt. Stewart completes putting him back into the lifeboat, the boy is again wearing the life-jacket.

When the raiding party lands, the German guards are patrolling with bayonets fixed (which they shouldn't be doing anyway). The next time you see one of the guards moments later, the bayonet has disappeared.

As Lt. Ward Stewart arrives on the dock to meet his new command, two Gato class submarines are seen leaving the dock. From the camera on the dock, they are traveling at, roughly, full reverse (stern first). The shot then alternates several times to the boats obviously moving at, more or less, full ahead (bow first). It's pretty easy to tell which end is which on a WW2 era submarine.

When the film begins, Stewart has his PT Boat attack a Japanese submarine. During the attack he drops five depth charges, and all at a high rate of speed. The film then shows the first charge sinking in water with no sub in the picture. But the subsequent four charges all managed to end up around the conning tower of the sub. To have accomplished this feat Steward would have had to have parked his PT boat over the sub. Rather, at his speed Steward should have been able to get at least one in close proximity to the sub, and perhaps even two, but certainly not four.

When the submarine submerges after being ambushed by the Q-boat, they are lying on the bottom and the captain passes the word that 'the smoking lamp is lit' for 10 minutes. Since WW-II era submarines did not have any form of air purification equipment on board, no submarine commander would ever authorize smoking on board whilst underwater, as this would quickly use up the limited air supply on board the boat. Smoking was only allowed while surfaced and the men had to be outside the hull, either on deck or a specific section of the after section of the conning tower known colloquially as the 'cigarette deck.'

Not surprisingly given the time of production, the German soldiers defending the 'secret base' are not using German weapons (e.g. they are frequently shown firing American-made Browning machine guns).

When in the office after PT duty when reporting for duty, Tyrone Power is wearing the twin dolphin submariner badge. As he hadn't been through submarine school, he would not have that badge.

With the submarine on the bottom the captain (Conners) orders fuel, debris, and clothing be jettisoned to confuse the destroyer. The flotsam is shown floating out of the submarine and to the surface. The purpose of this is to convince the enemy that the submarine has been hit and sunk. In the debris is seen what is apparently a dummy made from dungarees etc. It seems that this would be counterproductive because once the enemy found the dummy they'd know for sure that all the debris was fake, the sub had not be sunk, and would recommence firing depth charges.

Having swum underwater to avoid burning oil on the surface, Tyrone Power gets back on board the submarine to find the captain injured, he takes a cigarette case from his shirt pocket, opens it and give the captain a cigarette which is dry.

Steward and Oliver are caught on the wrong side of an oil slick that is on fire. They swim under the fire, but as they do, there is NO light coming down from the surface of the water, where the fire is supposed to be.

Lt. Stewart drives a metallic blue car. When he arrives at the dock and parks before the seaplane, the car is gray. In the next shot when Lt. Connors comes to greet him, the car is metallic blue again.

When Steward's sub comes across the German Q-boat, the Germans open fire. They fire at least 16 times if not well over 24, yet are not able to hit a stationary sub at fairly close range. These commerce raiders were much better shots than this and undoubted would have sunk the American sub. For 1943 this is probably more wishful, hopeful, patriotic thinking than reality.

When the schoolgirls are shooting their arrows in the archery class (c. 61 minutes) they are fired at an angle of about 45 degrees. Because of the effect of gravity these arrows would fall well below their targets and not, as in the film, hit them with so much success.