I'm just getting started with this game/series and, I'm confused about an aspect of the rules for corps assault (sorry for the novice questions). As I understand it, when a single unit is activated, the unit may attack in conjunction with its movement (i.e., if during a unit's movement it finds itself adjacent to an enemy unit it may attack, provided that the attacking unit has sufficient movement remaining). So, do corps assaults work the same way, or must all units that are to participate start the phase adjacent to the enemy unit? I'm sure that the answer is somewhere in the rule book, but I've not yet been able to find it. Thank you for any clarification.
Yes, for an Assault action, all units that attempt to participate must be immediately adjacent to their enemy. A corps or division leader must be present on the stack to initiate, and rolls his command to see which units may actually accept their orders and participate.
If there are additional hexes adjacent, and you are within range of an Army Leader, you may take a subsequent step to attempt a Grand Assault in order to use the additional units from more than just the original hex.