War machines in Heroes V.

Everything is clear about the ballista (or rather, nothing is clear), but tell me how a first aid tent can restore (revive) a unit. You can apply a bandage during first aid, but I don't know how it can revive. In our hospitals, resuscitation is powerless, but here there is some kind of magical first aid tent. I'm for it restoring health, not reviving, like in Heroes of Might and Magic III.