When Ensign Parker shoots down an enemy bomber during the air raid while he has been inhaling laughing gas, actual video simulating Ensign Parker's success is actually an American B-17 bomber being shown shot down.
When Binghamton gets sprayed while looking out the window, there is a wall behind him with a map on it. As he walks way their shadows are on it. Yet on an inside shot, they're seen leaving the window behind the Capt's desk.
The wall of sand bags outside the air raid shelter moves when someone touches them. Proving that they're not filled with sand but just props.