Thomas Wilhelm, A Military Dictionary and Gazetteer
“ Iron plates 1 inch thick, oak from 8 to 10 inches thick, a good wall a foot thick or a firm bank of earth 4 feet thick, will afford secure cover from grape-shot, from any but the largest guns at short ranges. The common musket will drive its bullet about a foot and a half into well-rammed earth, or it will penetrate from 6 to 10 half-inch elm boards placed at intervals of an inch. The penetration of the rifled musket is about twice that of the common musket. A rope matting or mantlet 31⁄2 inches thick is found to resist small-arm projectiles at all distances ”
