On the level when you are in the amphibious assault vehicles once you get onto the beach, the deepest left front crater (I'm not quite sure, but if not then just try all the craters) if you stand in it (i jumped as well) eventually you will start to hear some weird ass stuff. Then a bunch of those lion statues that are seen all around during the Jap campaign will show up and inside their mouths are the laser guns. My friend and I have done this on single player. I don't know if it works on co-op. Don't try to stand in the small craters, only the large ones filled with water. Don't hold me to it, maybe it was a glitch in the game or something, but it was pretty sweet.