Blast from the past. US Marines in WW1 don protective masks after German gas attack.

pic via HistoryWars Tumblr Page.

US Marines respond to a gas attack by the Germans and withdraw protective masks. The photo was taken in 1918 near Verdun.

Three things "modern" era (mid 80's on) Marines have never faced and I hope never will.  Gas attacks, heavy artillery bombardments and enemy close air fire.  Playing the worst case scenario card,  in the next war you have to wonder if we might see all three.