From USMC.mil:
AR RAMADI, Iraq — Three Marines with Company I, 3rd Battalion, 7th Marine Regiment, patrol behind a unit of the local Iraqi Army during a combined mission Jan. 17. The patrol was part of the training that the Marines are conducting with the IA to prepare them for providing security for their country. Photo by: Cpl. Shane Suzuki
Notice the 12-gauge the lead Marine has slung for easy access in addition to his M16/M203. I think he means business.

I’m guessing that shotgun is probably a ‘door knocker’.
Ah, the joys of patrol. Can’t say I miss it that much.
Yeff beat me to it. The shotgun is most likely along in case they have to do any door breaches. Doesn’t mean they don’t also have any 00 for it, though.
During any serious exchange of views…………nothing emphasizes the validity of your position like a load of buckshot at close range. DDOOHH!! I see your point!
HEY IM ON THE INTERNET!!! IM THE SECOND (SHORTER) GUY IN THAT PATROL!!
Jerry: Are you really a shorter guy? When I posted this someone said you looked pretty short for a Marine. I said it was maybe because you were walking in that ditch-like depression. Thanks for reading and thanks for your service.