Scales like iron breastplates: the Greek text says “breastplates like iron breastplates” (using the same word twice). Besides this passage and 9.17, the word occurs also at Eph 6.14 and 1 Thes 5.8. War horses sometimes wore breast shields to protect them from the enemy’s spears and swords. Instead of scales, something like “body-armour” (New Jerusalem Bible) is preferable. Biblia Dios Habla Hoy translates “their bodies were covered with a kind of iron armor,” or the translation can be “their bodies were covered with what looked like pieces of metal used to protect the chests of people.”

The noise of their wings: for a similar description of the noise of locusts’ wings, see Joel 2.5. In some languages this phrase will be rendered as “the flapping (or, whirring) noise of their wings” or “the noise that their wings made as they flew.”

The noise of many chariots with horses rushing into battle: a chariot was a two-wheeled vehicle pulled by one or more horses. The loud and rustling noise made by the wings of these locusts sounded like many horse-drawn chariots rushing into battle. The noise in some languages will be described with an adjective or an ideophone. An alternative rendering is “the rattling noise” (see Nahum 3.2). Chariots in many languages is translated as “horse-drawn war carts” or “war carts (or, wagons) pulled by horses.” So this clause may also be rendered as “the whirring (or, rattling) noise of many horse-drawn war carts racing (or, dashing) into the battlefield.”

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .