Regina Maria Pia-class ironclad

Line-drawing of Regina Maria Pia in her 1888 configuration

The ships of the Regina Maria Pia class varied in their dimensions. Regina Maria Pia and San Martino, built by the same shipyard, were identical in size, while Castelfidardo and Ancona, though each built by different shipyards, also were identical. The first two ships were 75.48 meters (247.6 ft) long between perpendiculars and 81.2 m (266 ft) long overall, and they had a beam of 15.24 m (50.0 ft) and an average draft of 6.35 m (20.8 ft). Castelfidardo and Ancona were 76 m (249 ft) between perpendiculars and 81.8 m (268 ft) overall, with a beam of 15.16 m (49.7 ft) and a draft of 6.35 m. The first two ships displaced 4,201 long tons (4,268 t) normally and up to 4,527 long tons (4,600 t) at full load, while Castelfidardo displaced 4,191 long tons (4,258 t) normally and 4,527 long tons (4,600 t) at full load. Curiously, Ancona was the lightest ship normally, at 4,157 long tons (4,224 t), but the heaviest at full load, at 4,619 long tons (4,693 t).[3][4]

The ships were constructed with iron hulls. They were protected by iron belt armor that was 4.75 inches (121 mm) thick and extended for the entire length of the hull at the waterline. The battery deck was protected by 4.3 in (109 mm) of iron plate. Each vessel had a crew of 480–485 officers and men. The ships were initially schooner-rigged to supplement the steam engine, though their masts were later reduced to a barque rig. Ultimately, they lost their sailing rig completely, having it replaced with a pair of military masts with fighting tops.[3][4]

The ships' propulsion system consisted of one single-expansion, two-cylinder steam engine that drove a single screw propeller, with steam supplied by six coal-fired, rectangular boilers. The boilers were trunked into a single funnel placed amidships. Her engine produced a top speed of 12.96 knots (24.00 km/h; 14.91 mph) from 2,924 indicated horsepower (2,180 kW). Each ship had a capacity of 485 long tons (493 t) of coal, which allowed them to steam for 2,600 nautical miles (4,800 km; 3,000 mi) at a speed of 10 knots (19 km/h; 12 mph).[3][4]

The Regina Maria Pia class were broadside ironclads, and they were initially armed with a main battery of four 72-pounder smooth-bore 8 in (203 mm) muzzle-loading guns and twenty-two 32-pounder rifled 164 mm (6.5 in) muzzle loaders, though their armament changed throughout her career. Most of these guns were placed on the broadside, but two of the 164 mm guns were mounted in an armored bunker forward and a third was placed in a similar mount at the stern, as chase guns. The ships were also fitted with a ram bow that was 3 m (9.8 ft) long.[3][4]

In 1871, all four ships were re-armed with two 220 mm (8.7 in) muzzle-loading guns and eight 8 in muzzle-loading guns, with a ninth 8 in gun added in 1880. Regina Maria Pia and San Martino were later re-equipped with eight 6 in (152 mm) quick-firing (QF) guns, five 4.7 in (120 mm) QF guns, four 57 mm (2.2 in) QF guns, and eight 37 mm (1.5 in) Hotchkiss revolver cannon. In 1884, Castelfidardo received the same battery of light guns, though she had a sixth 4.7 in gun. When Ancona was similarly re-armed, she only had two of the 37 mm revolver cannon. All four ships were also equipped with three torpedo tubes, with the exception of Castelfidardo, which received two tubes.[3][4]