I know they had White Phosphorous rockets & grenades which served the purpose of marking targets.
I think it would be cool to have a 'radioman' feature enabled (perhaps buy with vehicle perks) that allowed you to call in artillery (say for instance, 88's or 105mm's) from the most nearby base if it is in range. Stick a few extra 88's on a base for the purpose of launching HE rounds, give a little map (similar to "Viet Cong") or a little extra cursor on the kneeboard to mark for arty and then call it in. Each arty strike costs X number of points...make it enough (say 15-20) that you won't waste arty shells on useless or non high value targets, similiar to how it was actually done.