The Defence-class ironclads were a class of two warships built for the Royal Navy between 1859 and 1862. The ships were designed as armoured frigates in response to an invasion scare sparked by the launch of the and her three sisters in 1858. They were initially armed with a mix of rifled breech-loading and muzzle-loading smoothbore guns, but the Armstrong breech-loading guns proved unreliable and were withdrawn from service after a few years.
Both ships were initially assigned to the Channel Squadron, but was transferred to the Mediterranean Squadron in 1864. The ships were rearmed in the late 1860s after the completion of their first commission. They alternated between assignments with the fleet and guardship duties with the First Reserve for the rest of their careers. Resistance was the first to be paid off in 1880 and was used as a target for gunnery and torpedo trials beginning in 1885. She was sold for ship breaking in 1898, but wrecked en route to the breaker's yard. was paid off in 1885 and she became a stationary training ship in 1890 until she was sold for scrap in 1935.
Background
In 1859 the Admiralty was not yet convinced that the very expensive (£377,000) s, which cost more than twice the wooden, steam-powered ships of the line, had to be accepted as the norm. They noted that the armour plate of the Warriors was adequate to deflect all ordnance currently afloat, and high speed was not necessary to prevent existing wooden ships from massing their fire against the ironclads. Their Lordships therefore requested a design which, while carrying the same armour, was smaller and slower, and thus cheaper, than the Warriors. Rear Admiral Sir Baldwin Wake Walker, Controller of the Navy, proposed that six ships be built to this design, but he was over-ruled and only two were ordered on 14 December 1859.
The Admiralty's decision saddled the Royal Navy with a pair of ships that could not operate with the Warriors in a tactical squadron and were inferior to the French ironclads then under construction. The naval architect Sir Nathaniel Barnaby, a future Constructor of the Navy, considered that a Defence-class ship was worth one quarter of a Warrior in terms of combat, although they cost about two-thirds as much.
Description
The Defence class was long between perpendiculars and long overall. They had a beam of and a draught of . The ships displaced and had a tonnage of 3,710 tons burthen. Unlike their predecessors, they were fitted with a ram in the shape of a plough. The ends of the hull were subdivided by watertight transverse bulkheads and had a partial double bottom. Each ship had a complement of 460 officers and ratings. The Defence class was shorter overall and displaced more than less than the Warrior-class ironclads.
Propulsion
The Defence-class ships had a single two-cylinder trunk steam engine made by John Penn and Sons driving a single propeller. Four rectangular boilers provided steam to the engine at a working pressure of . The engines produced during sea trials which gave the ships maximum speeds of . They carried of coal, enough to steam at .
The ironclads were barque-rigged and had a sail area of . The lower masts and bowsprit were made of iron to withstand the shock of ramming. Both ships could make about under sail alone. To reduce wind resistance while under sail alone, the funnel was semi-retractable. Similarly, the propeller could be hoisted up into the stern of the ship to reduce drag while under sail.
Armament
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 68-pounder weighed and had a range of with solid shot. During construction the armament was changed to six (Defence) or eight (Resistance) of the new Armstrong rifled 7" breech-loading 110-pounder guns, ten 68-pounders, and either two 32-pounder smoothbores (Resistance) or four breech-loading guns (Defence). The innovative 110-pounder, whose shell could reach was in short supply when the ironclads were launched, and poor results in armour-penetration tests halted plans to fully equip the ironclads with this gun. Furthermore, the 110-pounders proved problematic in service. They were labour-intensive to load and fire, and some of them blew up when other ships used them in action. After that, they were only used with a reduced propellant charge, which left them useless in practice.