LAAD "gunner" is the guy with the ground-to-air anti-aircraft missile assigned as part of a LAAD platoon to take down enemy aircraft and other sub-sonic aerial targets (e.g. drones). For the most part, it is a very, very boring duty assignment considering that the US gains air superiority within days of all conflicts to include Vietnam. The LAAD Platoon is part of the Marine Air Defense Battalion attached to each of the four Marine Aircraft Wings. MAD Bns mission are the defend Marine expeditionary air fields from enemy air attack. Again, not a lot happening.
During training LAAD gunners get to fire inert training missiles and later live missiles at target drones. In the past the Stinger Missile was the primary weapon system. I believe that has been replaced with a more advanced system.
When they are not doing their main job, they clean their weapon systems, dismantle them and put them back together. They get classroom time and simulator time.
Re: Artillery - somewhat the same scenario except artillery rounds are cheaper and more training practice with live rounds are available. Additionally, the early stages of a battle involving Marine maneuver forces has artillery fire mission support. More likely that you are involved in combat in an artillery Bn than in a LAAD platoon. Lots of heavy handling since arty shells and powder packs are pretty heavy. Cleaning the pieces (guns) isn't easy due to their size. A gun crew works together as one to load, fire, reload, fire, etc. Target coordinates come from the fire control officer and passed down via field comm. Each section has Staff NCOs to set and check all fire coordinate settings on the guns that they receive from the fire control direction center to ensure the rounds go where requested and not on top of friendlies. What job you get in the artillery battalion will determine just what you will be doing.
That is how it works in the two areas of Combat Support that you asked about. There are others as well: Armor, AAVs are two more.
Lieutenant Colonel, U S Marine Corps- Retired