Horses ready for battle were outfitted with a metal skirt to protect the animal from arrows or spears. These breastplates added to an army’s aura of invincibility. That is definitely the case here. There is nothing you can do to stop or overcome an army of locusts—and certainly not if these locusts are actually demons.
9 they had breastplates like breastplates of iron, and the noise of their wings was like the noise of many chariots with horses rushing into battle.