Battalions Special Rule: Each USA infantry formation on the board can take 3 'hits' before its actually taken off the table. An infantry formation includes any Infantry Squad, any Infantry HQ Squad, and any MG Squad. You can track this by any method you prefer - written lists, colored 'fluff' balls, chits, odd sided dice (non 6s or over size/undersized 6s from the size you're rolling for the game). Once a given Squad has taken its third hit, its removed from the table. Any morale check is then rolled as normal, with the minus appropriate to the loss. So Co. A of the 1st battalion is in position and taking hits. The 3rd Squad takes 2 hits. No problem, its marked with 2 losses. The 3rd Squad again takes a hit and now forces a roll on Morale with a -1 due to its losses For The Entire Company. If it fails, Co. A will rout as per the usual rolls; note that if its HQ is intact, it may use an order per normal rules to attempt to rally. If its HQ is destroyed or if it loses another full squad, it is destroyed as per pages 43-44 rules. As there are so many order counters for the USA, the HQ destroyed is an attempt to balance the problem of so many order tokens to spare. For the Cavalry, each Troop (Company) represents (2) Squadrons of (3) Squads each. For those, just give each Squad 2 hits without anything special HQ situation. In other words, once a cavalry unit routs, it can be 'reformed' by an order token or by the final roll at the tables edge.
Whichever solution you use, you should apply it to all such actions regarding very large commitments of troops. The additional advantage to this ratio'd forces rule(s) is that your club or games store/convention group can actually field all the units.