Everybody Loves Surplus Ammo Boxes

Yesterday we were getting some copies made and I found this in the back of the print shop. If any of the military folks out there can give me a better idea of how this ammo case ended up loose, I would appreciate it. I did not check to ensure it was empty, but this is definitely US issue.

Editor's Note: My wife has just informed me that we have quite enough ammo boxes at our house already. Under no circumstances am I to bring any back with me.