Seriously, the first and third guy are shooting over a grill of some sort. I presume you knew where it led, but it would seem to me that dropping brass and links down a grill on a piece of machinery that has to work, or you die, seems a bit risky, no?
The grill is nothing more than a way for air to circulate between the superstructure and the hull. Right now everyone is laying on the "superstructure" which actually sits above the pressure hull. You can walk between the superstructure and the pressure hull and if the casings fell through they would wash away when the ship submerged.
This is something unique to this class of submarines. It's actually there for a level walking surface and to make everything flush so that it isn't as loud when noise flows across. Otherwise you'd be walking between missile tubes.
What are those tubes/round "thingies" (Navy technical term), just this side of the sail? Do those carry the SEAL insert boats/subs? Or are they Tomahawk tubes? OBTW you wouldn't know a Chief Patterson whould you? He transitioned to aviation from subs and is in training here.