Just a mystery.
6lbgun, I wish I were smart enough to enhance the photo, but I'm not. You're right, read the letters and the puzzle is solved.
One person told me that because the wording was "curved" it was probably civilian. He said military wording was straight. I don't know if that is true or not.
Another person stated that it looked like a "battery wagon box." This theory is pretty much the same as Selma Brooke Gunner. This guy said it would be used to carry spare parts, just as Selma said. Selma calls it a "battle wagon," the other guy called it "battery wagon box." But look how small it is. What parts would you carry in it?
Its wheels are thinner than the other rolling stock pictured, so it was not, apparently, designed to carry as heavy a load.
It has a "roof." I can't tell what the roof is made of, but it might be made of some sort of "tin."
No person, evidently, rode on it, so it must have been hauled behind another wagon.
The whole contraption seems to be designed to keep out moisture -- which leads me back to a photographer's wagon, or some sort of artillery wagon used for items which were in need of escaping moisture.
Thanks for the thoughts. Surely, there are other pictures out there of the same type "wagon."