The U Boat is shown with a rear deck gun. After being depth charged by the destroyer the U Boat is shown with a forward deck gun.
Evidently they reversed the film when the B-17 was about to ditch. At least twice, the painted "K" on the side of the aircraft is reversed.
The periscope is not in the Control Room. The periscope is located in the Conning Tower above the Control Room.
There are no cabins aboard a U Boat.
The U-boat commander is drinking a dark wine, which he says is a 1933 Mosel. Mosel is a white wine.
Since they already surfaced, The U-Boat would have fired a few rounds from the deck gun to sink the small fishing boat. One torpedo, let alone 2, would have been impractical on a small target as this. Plus, torpedoes were too valuable and used on larger vessels.
The controls to launch the torpedoes on a German submarine are clearly labeled FIRE 1, FIRE 2, etc. in English.