Also, the Navy argument is a nice one, one I will happily accept. I didn't see the relation, but yeah, yeah, it's a really good one.
Still, doesn't a full auto feature on a military shotgun make sense? Whether or not it goes into TTW is incidental, but shouldn't it from logic?
Another thing about the utility of shotguns on ship, was that we we trained not to fire at the enemy on board but the metal deck plating and hull. This would cause a nasty ricochet effect and completely clear passageways. Also I served on submarine's and we were issued 12 gauge, although when I was temporally assigned to a few surface ships they where only issued small caliber weapons like the 20 gauge.
Also I would like to make one final point, this game take place years in the future, in an alternate timeline. So saying that, who knows if there military followed the same rules as our military.