[Rules] Armor joining an in progress assault hex

[JoeBuckeye]

How can an adjacent armor unit move into an already established assault hex?

I assume that it can activate and then move in but can it then start an assault resolution in that hex involving all the units already there (assuming the friendly units already in the hex have not activated this turn)?

This seems to be a pain to coordinate with INF since non-tank leaders can't activate armor units so if the hex is at full strength you would need to activate the INF first and have one move out (leaving other behind so no exiting fire) and then have another activation to move the armor in.