Generally, if it is a factory tailgate option, it should be a civilian model Bantam.
The military models had no tailgate, because they were amphibious - able to float with a 500 lb load.
But, a true Bantam civilian model trailer should have six stake pockets just inside the top lip, front, middle and rear, three on a side, for wooden stake slats.
The tailgate on the civilian model is not a rectangle. It is flaired at the top, following the body lines. The civilian tailgate also has only two vertical support ribs embossed into it, like what you see on the front panel, and they do not extend full length at the top or bottom. This one has three that extend full length.
The support brackets are similar to those for very early civilian trailers, which were later replaced by larger stamped pieces that incorporated holes for the taillights.
On the outside of a civilian model, there are only three tie down loops on the sides, whereas the military model has four tie downs.
A military trailer will have brakes for parking and handling, while the civilian model has no brakes, just a hub.
A military model has shocks, while the civilian model lacks them.
A military model has a rear landing gear leg for stability, and again, the civilian model lacks them.
By "military model", I'm referring to the original WWII and M100 series trailers. not the M416, because there was no civilian version of the M416.
And that bring up the final nail in the coffin. The photo appears to show a flat fender. The WWII and M100 trailers had round fenders (as did the civilian model). Unless someone installed flat fenders, then this is an M416 trailer that someone added a tailgate to.