After playing an ACW game the other day I've decided that the ideal organization/deployment is to have brigades with 5 regiments and to deploy them on a 2 regiment front, keeping three regiments in reserve. That way if the two leading regiments become shaken your brigade is still not broken. You can then send two fresh regiments forward while the commander tries to rally the shaken regiments. with luck you can keep the brigade in action for a long time.
It's not just about gaming. Historically a lot of ACW brigades did have five regiments in them and the tactical doctrine of the times called for brigades to be deployed in two or three lines of regiments and they drilled how to have the rear line relieve the front line. If a game allows for historical tactics to be used to the player's advantage I see nothing wrong with doing so.
While ACW is not my thing, there's nothing wrong with what the OP suggests and historical to-boot.
The title to the post is perhaps unfortunate as it suggests (to some) a particular way of gaming.
.. I think that the poorest he that is in England hath a life to live, as the greatest he; ... and I do think that the poorest man in England is not bound in a strict sense to that government that he hath not had a voice to put himself under
Sending reserves sounds easy but was a very difficult operation in reality. The American Drillbook demanded that the front units create gaps by pulling back the flank companies, the second line regiments would march in these and deploy into line with the former front units retreating. Nice on a parade show.
This operation required careful timing and in practice rarely happened as laid down in the books. A misunderstood order and the front line unit retreated in panic, disordering the reserve too.
And even if the front unit did not break very often the reserve became mixed up with the shaken unit and control was lost. Typically the reserve ran to the front in small groups and the shaken front unit retreated with little or no order.
The European observers reports are not very impressed by the passage of lines done in the ACW battles. Describing milling herds of men mixed from front and reserve fighting with no regimental formed bodies.
I have a question for those of you more in the know: how does this 'passage of lines' malarkey apply to other periods covered by the BP rule i.e. what 'should' BP brigades look like in different periods?
Just curious really!
Clausewitz Rules, OK? The future is the past - with GPS - Colin Gray
As Invisible Officer notes, the by-the-book "Passage of Lines" was a finicky manuever and rarely done in battle. However, there were a number of other quick-and-dirty methods for allowing one regiment to pass through another in reasonably good order. There are numerous references in the histories of fresh regiments relieving spent ones so it was clearly possible.