This rule was invented by Mike McGinnis and Ed Whitaker in the 1990's for use in Napoleon's Battles. Since that time I have tweaked it a bit here and there. (Well, actually, this is now (December 2001) getting beyond the "tweak" point. The biggest, most recent change is getting rid of the fatigue mechanism in favor of requiring the attacking and advancing division to do certain things.)
The general philosophy of this rule is to keep the command system as simple as possible while keeping the general impact of differing skills of the commanders. Toward this end, there are no written orders (in the sense of "attack the town of so-and-so") or markings on maps. Instead, each organization is given one of several orders (each discribed by a single word). Each order has advantages and disadvantages. Changing from some orders to others is automatic, but the majority depend on a dice roll, which is based on the skills of the officers involved.
The four orders are Attack, Defend, Advance, and Maneuver.
A division that has an Attack order can move, shoot, and contact the enemy with only one restriction: at the end of the Movement Phase, at least one unit in the division must be in command radius of the Division Commander AND
(Note: the Attack requirements are a total rewrite of the original, fatigue-oriented rule, as of December 2001.)
A division that has a Defend order can shoot, but cannot contact the enemy. No component of the division can end its move closer to the enemy than the closest component of the division was at the start of the turn. In addition, the division cannot move at all unless there is at least one known enemy combat unit within 3600 yards of some component of the division.
However, cavalry units in a Division under Defend orders can charge (i.e., contact the enemy). Note that this is NOT a license for non-charging cavalry to get closer than the closest unit was at the start of the Movement Phase; the only way for Cavalry to "violate" the "no closer" requirement is to charge to contact. Note also that a Defending division determines where the closest enemy is before any such charges are made; you can't invoke this exception and then claim that infantry in the division can charge as well.
(Note: the Defend order no longer includes fatigue recovery, since there is no longer any fatigue.)
A division that has an Advance order cannot shoot and cannot contact enemy troops. If there are known enemy within 3600 yards, then the Division must end the Movement Phase with at least one unit at least 300 yards closer to the enemy than the nearest unit in the Division was at the beginning of the Movement Phase. It can without rolling change to Attack at any time, including during the enemy turn.
(Note: the Advance order now requires some movement toward the enemy.)
A division that has a Maneuver order cannot shoot and cannot contact enemy troops, but can otherwise move without restriction. It can without rolling change to Defend at any time, including during the enemy turn.
The player can attempt to change the orders of any or all of the divisions during the command phase. To change a command, the player must roll equal to or lower than the divison commander's command rating (which is on a scale of one to five).
If a division fails to change its order, the player can then attempt a "saving throw" by rolling against the command rating of any superior commander(s) in the line of command above the division.
The distance is measured as if a cavalry skirmisher moving from the superior commander to the division commander; both penalties for bad terrain and bonuses for road movement apply. The path cannot pass through enemy units or between two enemy units that are less than 300 yards apart.
Note that while a given division can have any number of save attempts by the commanders above (say one each from corps, wing, and army), each commander can only make one save attempt per turn.
A division that has all of its combat units put out of action (destroyed and/or routed), or which is exhausted or collapsed, instantly changes to Defend.
A division on Attack Orders that is physically incapable of fulfilling the requirements for Attack (due to being too far away, for example) instantly changes to Advance.
A division on Advance Orders that is physically incapable of fulfilling the requirements for Advance (due to being blocked by impassible terrain, for example) instantly changes to Defend.
Note that a division can drop from Attack through Advance to Defend all at once if it is incapable of either Attack or Advance.
The focus of this rule is on the division commander. The corps, wing, and army commanders are treated as supports. This is the reverse of the usual command rule (and of real operations), in which orders flow down from the top. However, this rule is in line with what the players are in fact trying to do in the game, i.e., get a given division to do something. By treating the superior HQ's as supports, it focuses on the player and on the division commanders -- the players usually are the superior commanders. However, the players will also quickly discover that the superior commanders need to position themselves to observe the battlefield (have clear lines of sight) and be close to the critical action, in order to have a positive influence on events. And so the final effect of the rule is in line with actual operations, even though the mechanism is a little counter-intuitive.
Using Advance and Maneuver orders can be a great aid to the player. For example, if you are defending and want to close with the enemy without getting fatigued, give the division a Maneuver order during the command phase, move forward for one movement phase, and then automatically convert back to defend at the end of the movement phase. That way you can get around the "no closer" rule but still be in a firing position during the combat phase. It's not cheating, it's the way the rule is designed.
Cavalry have the option to charge while on a Defend order simply because that is the only way mounted units can fight. Remember: just because a cavalry unit charges doesn't mean the rest of the division's infantry can then charge too. The "no closer" restriction is evaluated at the start of the movement phase, not after the cavalry charges.
There are two orders, Defend and Advance, that have some intimidating phrasing: "closer than the closest unit was at the beginning of the Movement Phase". This is not as ugly as it sounds at first. Just note how far away the closest enemy unit is at the start of the Movement Phase; if Defending, then no unit can end up any closer to the enemy than that; if Advancing, then some unit has to end up closer than that distance. (If anyone out there thinks up a more graceful way of saying that, please let me know.)