Formidabile: a French-built Italian ironclad

Formidabile and her sister Terribile were built at a French Mediterranean yard and evolved from proposed floating coastal-defence batteries into mobile armoured corvettes. Cutting the intended battery from thirty guns to twenty helped turn a static defensive concept into independently mobile warships. At roughly 2,600 tons normal and up to about 2,800 tons, each combined six boilers and a roughly 1,000-horsepower single-expansion engine with a full schooner rig. Under steam Formidabile could make about 10 knots and cover roughly 1,300 nautical miles at that speed, while sail extended her practical reach. Her battery comprised four 203 mm smoothbores and sixteen 160 mm guns behind a belt about 100-115 mm thick. The design illustrates both the quality French yards could deliver and the operational value of retaining sail alongside early steam propulsion.