Plot hole: After the marines fire into the crowd and things die down, Jackson tells his men to stay down because of possible snipers. Yet he is standing upright the whole time. Not the best tactical move. One sniper and the mission loses its commanding officer.
Plot hole: In the movie the German sub is in the middle of the Atlantic about 1500 miles from the American coast the American submarine is an S-Class boat which had a top speed on the surface of 12 Knots even less underwater and it spent part of the trip submerged. This means that it would have taken them at least 5 or 6 days to reach the German Sub. This is 1942 There would have been dozens of other German subs a lot closer who could have come to their rescue.