It is an 1916 American AA gun, semi-copied from the French 75mm field gun, and mounted on a White 2&1/2 ton truck chassis. 51 examples being supplied before the fall of France. Then again, the French then copied the American bastardization of their gun for their own AA gun in 1917, some of which they also seem to have put on trucks.
... More and more, people around the world are coming to realize that the world is flat!