This is a bit confusing, and I think that should be properly visualized there. But the question is how to do that and make it clear?
My first thought was to display something like:
Where 5 is amount of other assigned units, 16 is amount of units that can be handled by commander and 3 is amount of assigned artillery units. But this may be not clear enough...5 / 16 + 3
I don't know, is there limit for assigned artillery units? If yes (if not then maybe should be?) then it could be shown like this:
Maybe using also / instead icons that shows normal and artillery symbols.5 / 16
3 / 16