 The armament of the Defence-class ships was intended to be 18 smoothbore, muzzle-loading 68-pounder guns, eight on each side on the main deck and one each fore and aft as chase guns on the upper deck, plus four Armstrong 40-pounder guns, an early rifled breech loader (RBL) design, as saluting guns. The 8.12-inch (206 mm) 68-pounder weighed 10,640-pound (4,826.2 kg) and had a range of 3,200 yards (2,900 m) with solid shot. During construction the armament was changed to include six (Defence) or eight (Resistance) rifled 110-pounder guns, ten 68-pounders and either two 32-pounder smoothbores (Resistance) or four breech-loading 5-inch (127 mm) guns (Defence). The innovative 9,520-pound (4,318.2 kg) 110-pounder, whose 7-inch (178 mm) shell could reach 4,000 yards (3,700 m) was in short supply when the ironclads were launched, but poor results in armour-penetration tests halted plans to fully equip the ironclads with this gun. The 110-pounders blew up when other ships used them in action, were labour-intensive to load and fire, and were henceforth only used with a reduced propellant charge, which left them useless in practice.
