Plot hole: When the Major and Wadislav walk up the stairs in the German mansion they are met by a pair of German officers who say something to them. Wadislav then tells the Major that he couldn't understand a word they said. What they actually said was 'Nice weather, wouldn't you agree?' Wouldn't you think that a man who speaks German well enough to convince the guards in a German HQ would understand such a simple phrase? Wadislav was chosen specifically for his ability to speak some German.
Other mistake: After Reisman beats up Franko at the beginning, Reisman asks the guard to have 2 prisoners take him back to his cell. After that, Reisman says "lets see if they can do some close order drill now." During the drill, there are 11 prisoners marching instead of 9 as 2 of them took Franko to his cell.
Other mistake: Just as the attack begins on the chateau a German officer is shown for a second time shouting for everyone to head to the cellar. Immediately after this, a younger officer is shown motioning toward his holster, as though he intends to draw his gun but there is no gun in it.
Continuity mistake: At the very end, Jefferson is shot after dropping grenades into the vent pipes. He lands face down with his right arm bent and his right hand right next to his helmet. The camera cuts to those left on the truck. When it shows Jefferson again, his hand is now about a foot away from his helmet.
Revealing mistake: When the 25 pounders fire, there is no recoil.