On a few patrols, while deployed in 08/09, I had a Mossberg 500. One of the ones I carried was a short barreled one, and another was a "full size" one, and it depended on if the assigned person came out on patrol or if someone was covering down on their weapon system.
Due to the current R.O.E. (Rules of Engagement) at the time, and the "transition of authority" we were required to have the capability to use less lethal rounds in some situations. Being as such, we were required to have "X" amount of weapon systems capable of deploying less lethal munitions, which were shotguns and M203 grenade launchers Our shotguns still had shot in the tubes, but the first round was less lethal.
Shotguns are one of the most versatile weapon systems around, and when used in the proper matter, most effective. What other weapon system (portable) can fire buck, slug, less lethal, exploding, ect?
(BTW: The couple of times I carried it, I also had my M4 slung in case of further engagements)
M&P 15, XD:M .40cal, Mossberg 500 with Knox tactical stock and now also a XD:M 3.8 in .40cal...