Continuity mistake: After Donald Sutherland finishes viewing the soldiers at the parachute school the dirty dozen march right past Robert Ryan. The very next scene shows them just starting to march past him again.
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: Towards the end Reisman gets shot in his right shoulder, which bleeds. The blood disappears between shots.
Continuity mistake: When Reisman meets the dozen for very first time, the sun is changing in almost every shot.
Continuity mistake: After Pinkley plays a general the sun on the ground changes between shots.
Continuity mistake: Sgt. Bowren's right hand moves to his holstered pistol as Maj. Reisman and Posey begin their close combat knife training. The next long shot of Posey, Reisman and Bowren shows Bowren reaching for his pistol again.
Continuity mistake: Pinkley waits outside the chateau by the kubelwagen with his hands behind his back, approaches the driver's side and places his right hand on the door. The long shot shows him repeat the movement.
Revealing mistake: When the 25 pounders fire, there is no recoil.
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.
Answer: Detonators for explosives.
stiiggy