Crossroads - S1-E5
Revealing mistake: When Easy is paddling across the river to aid the British soldiers, there is a shot where the person closest to the camera (Bull Randleman) appears to be rowing, but there is nothing in his hands.
Revealing mistake: When the first tank comes during the final battle, look carefully at the German sitting on it and you will see that he's actually a dummy.
Revealing mistake: In "The Breaking Point," Lipton is narrating the bombardment of the woods right outside of Foy. Just before he says, "What I saw that day," at 30:55, you see a section of a tree explode, but when the debris (i.e. the splinters of wood and snow) clears you see that the "blown up" section of the tree is unharmed. (00:30:55)
Revealing mistake: When trying to take the warehouse, we see a German machine gun position in a lower window. Pay close attention to the brickwork below the window. There are several marks visible that all end up with a bullet hole in the middle of them, hiding the charge for the effect. (00:14:30)
Replacements - S1-E4
Revealing mistake: Just as the one soldier is sent flying over the wooden fence surrounding a building, you can see break away marks on the post where he will hit it. (00:34:40)
Replacements - S1-E4
Revealing mistake: Just as the Tiger fires its second shot and hits the garage, look closely and you can see where the break in the wall is going to appear. (00:32:05)
Day of Days - S1-E2
Revealing mistake: When placing the German grenade into the barrel of the German, gun you can see the cord used to set timer is still attached. (00:36:40)
Suggested correction: The cord doesn't have to be fully removed for it to work so showing it like that is not a mistake. The grenade will smoke quite a bit if the primer is ignited so even if the cord isn't fully removed they'll know quickly enough the pull was hard enough to ignite it.