structural:summarization, linguistic:paraphrasing
Reserves at various levels

Reserves are kept and employed at all levels, from a platoon held back from a company level engagement, to whole army corps consisting of armoured and mechanised divisions which are held in reserve with the purpose of exploiting a breakthrough or containing an enemy advance. Typically what is a reserve for one headquarters is not the reserve for a higher headquarters (though depending on the setup they may be). So if one of a battalion's companies is held in reserve during a battle, the company is considered to be a reserve for the battalion but not for the brigade or the division, since it is committed to action in its parent battalion sector.