he vessels of the River Defense Fleet were intended to be used as rams,[11] and they were known as cottonclad warships.[12] Their conversion into warships involved the addition of 1 inch (2.5 cm) of iron plating to the bow, backed by 4 inches (10 cm) of oak planking on a framework of 1 square foot (0.093 m2) timbers. The engines and boilers were protected by an inner bulkhead of one-foot-square timbers with an outer bulkhead of 6 by 12 inches (15 cm × 30 cm) timbers. In between the bulkheads was cotton.[13] General Earl Van Dorn's armament consisted of a single 32-pounder cannon on her bow,[14] which was a common naval gun that was smoothbore and muzzleloading.