ORIGINAL: jimcarravallah
Agree with dismounted troops.
Not certain about the replacement during battle. The fatigue, morale, and cohesion calculations and the merging of heavily damaged units into peer organizations more or less allow the "operationally available" manpower to vary over the period of a battle in the same manner that healthy soldiers are sent back to the fight or reassigned to a new commander when original unit cohesion is unattainable due to overall unit losses.
But, I'm presuming that, other than in the movies, new recruits entered a unit only during significant lulls in battle.
Replacement of equipment is intriguing. Over longer scenarios it could take into account operations such as heavier repair of battle damaged / fatigued equipment (which brings in consideration of repair parts, maintenance manpower, and maintenance organization in the game software).
As far as "reserve" equipment, the US Army has a concept of battlefield reserve, with a small percentage of equipment (equipment count significantly lower than the number necessary to stand up even the smallest unit organization under the command if soldiers were available to man it) assigned to a higher command structure. It is brought forward as a "loaner" to replace a piece of equipment that had to be towed to the rear for repair.
It was still part of the maintenance operation rather than having enough available to replace totally destroyed equipment with newer units.
Major SNAFU:
I have read any number of accounts where reserves and even new replacements were fed directly into the line. The would arrive at the relevant CP and most often be picked up by an NCO and troops that had come back from the line to obtain supplies and food, and then would be led back to the line and placed into foxholes with little or no orientation as to even where the MLR was. At best, their foxhole mate has been on the line for a while and could fill them in a bit.
This, of course, applies to infantry. But I believe even in the book "Death Traps" it describes that repaired and repainted shermans were fed into the line with green crews to replace casualties during an operation - not between operations. At best they were told something like "the enemy is in that direction...." and off they would go.
So I would like to see for multi-day operations an ability to have a certain number of troops and equipment replaced on the line. I would not be a huge number, but getting a couple of shermans back on day 3 that were lost on day 1 is not unrealistic. A sherman could be taken out by one penetrating round taking out the crew. They would patch it, paint over the blood and a new crew would take it back into the line.
It's the repair and repainting I was speaking of when discussing perhaps allowing some equipment to return. Certain types of "kills" on a tank, truck, or a gun don't necessarily destroy the weapon system or harm the crew but make it inoperative and in need of repair (consider a flat tire on a truck as a relatively minor example).
Particularly in the case of penetrating rounds, the repairs are significantly more complicated than "patching and painting" and would take longer to perform.
If a round can kill a crew with the debris from the armor it shatters to penetrate the tank it can also do significant damage to those things inside the tank necessary for it to fight effectively.
The hole on the outside of the area hit is much smaller than the crater on the inside the effective penetration created. In effect a penetrating round turns the inner armor into shrapnel (determined by the weight and velocity of the penetrating projectile and the hardening of the armor), which kills the crew in close proximity and does significant damage to hydraulic lines, communications equipment, controls, sights, and turret, automotive, and gun control mechanisms / motors.
It takes time to evaluate what is necessary to return the platform to some form of operational state (ability to move and shoot as a minimum) and more beyond that to repair / replace components necessary to return it to that state.
If it's a mobility kill, where the track was cut (often the result of damage in a minefield), the time is relatively short so long as enough links of track or a road wheel on hand to repair the a mobility kill (the reason why some tanks have lengths of track and spare wheels hung on their front glacis). The crew can usually return the vehicle to operation in a few hours with immediate track repairs.
More significant damage (suspension, interior, control mechanisms, armor) require more refined skills and as a minimum the transport of technicians, parts, and equipment to the damage site, if a repair is capable of being performed in place.
More time yet is necessary for recovery (towing / restoring minimal movement by crew to drive the vehicle to the rear) and repair at a static repair point.
None of this is currently modeled directly in the game.
Though not explicitly modeled, there's a flavor from the unit effectiveness measures for a combat unit, and the recovery times necessary to restore a unit's combat effectiveness from those situations.
As far as combat replacements (manpower) being added, given the lag time between when a unit suffers a combat loss and the military bureaucracy could respond to that loss, I don't think including it in the game time scales is realistic.
I've seen a suggestion for a "campaign mode" concept to be designed into the CO system. As I recall, it would allow a player to take a unit that had serial battles inside a larger campaign to be taken from the first battle it faced to the last using the results of an earlier battle to define the strengths and weaknesses for the unit when included in a later battle. Replacements would definitely fit into that situation (in effect available at the start of the next scenario in the campaign).
But, there wouldn't be 100-percent replacement (or there'd be no sense seeing how a unit does in the "campaign") and given the time frame between scenarios, there could be a significant lag between the time a replacement is needed and one is available.