Like the previous two Close Combat games, troops are sectioned into units by what their special abilities are. For example a tank would be a unit by itself, while an infantry group would be another. The total number of units one can take to battle is limited from a max of ten to fifteen. It's all regulated by a system of requisition points and depends on your rank. Requisition points are predetermined and given to you at the unit selection screen after a mission.
Different units cost different amounts.
Units that have winterized gear for certain maps cost a lot more than their counterparts and armor units in particular are very expensive, costing half of your total points in some cases. As for rank it determines the maximum number of units you can have in play. For single missions and operations, rank doesn't change and you are stuck with the max limit for that rank. But in campaigns you can be promoted, thereby increasing the number of units you can command in later battles. Another thing that makes the game interesting, is which side you choose to play before the game.