The cavalry had a Red Cross wagon. The American Red Cross was not founded until 1881.
This movie takes place in 1868, the US army issue revolver was a 44 caliber cap & ball model, not a an 1873 Colt single action army model.
When Sgt. Bell goes to the tent for a drink of whiskey, and Sgt. Carrracart remarks that the still is small, Carracart instead takes a drink from a canteen. The canteen is a Scout model, made of aluminum, and was not manufactured until the 1900s.
At approx. 1:00:38. as a supply wagon and a Red Cross wagon are cresting the hill during the attack on the convoy, the shadow of a boom mike can be seen falling across the canvas covering of the first wagon.