Revealing mistake: As Sgt. Highway turns the dead body with a cigar in the pocket you can see its right arm move to avoid twisting. (01:38:05)
Revealing mistake: Near the end they land on the island. After they cross a bridge a soldier shoots an explosive and blows up a machine gun position. Just after that, look at the muzzle of Highway's rifle. It isn't open like it should be but has a type of plug to ensure only blanks can be used.
Chosen answer: Gunny Highway insisted that they all wear the same shirts as he himself was wearing. If they showed up in a different one, he made them go shirtless. The reasons for this were 1) to break through their rebellious attitudes and teach them to follow his orders, 2) to make them look and feel unified, and 3) to develop resourcefulness and adaptability in them.
Chanteuse66
To also display esprit de corp to other units gaining them respect from those units as well as command leadership.