HMS Northumberland was the last of the three armoured frigates built for the Royal Navy during the 1860s. She had a different armour scheme and heavier armament than her sister ships, and was generally regarded as a half-sister to the other ships of the class. The ship spent her career with the Channel Squadron and occasionally served as a flagship. Northumberland was placed in reserve in 1890 and became a training ship in 1898. She was converted into a coal hulk in 1909 and sold in 1927, although the ship was not scrapped until 1935.
Design and description
The Minotaur-class armoured frigates were essentially enlarged versions of the ironclad with heavier armament, armour, and more powerful engines. They retained the broadside ironclad layout of their predecessor, but their sides were fully armoured to protect the 50 guns they were designed to carry. Their plough-shaped ram was also more prominent than that of Achilles.
Northumberland was long between perpendiculars and had a beam of and a draught of . The ship displaced and had a tonnage of 6,621 tons burthen. Her hull was subdivided by 15 watertight transverse bulkheads and had a double bottom underneath the engine and boiler rooms. The ship was considered "a steady gun platform, able to maintain her speed in a seaway and satisfactory in manoeuvre". She was authorized a crew of 705 officers and ratings, but actually carried 800 men.
Propulsion
Northumberland had a two-cylinder trunk steam engine, made by John Penn and Sons, driving a single propeller using steam provided by 10 rectangular fire-tube boilers. It produced a total of during the ship's sea trials on 15 September 1868 and Northumberland had a maximum speed of . The ships normally carried of coal, but had a maximum capacity of , enough to steam at .
Originally designed with three masts, Northumberland was fitted with five masts until her 1875–79 refit when two were removed and she was re-rigged as a barque. Northumberland only made under sail, mainly because the ship's propeller could only be disconnected and not hoisted up into the stern of the ship to reduce drag, the worst speed of any ironclad of her era. Admiral George A. Ballard described the Minotaur-class ships as "the dullest performers under canvas of the whole masted fleet of their day, and no ships ever carried so much dress to so little purpose."
Armament
Unlike her half-sisters, Northumberland was armed with a mix of , , and rifled muzzle-loading guns. All 4 nine-inch and 18 eight-inch were mounted on the main deck while 4 eight-inch guns were fitted on the upper deck as chase guns. Both seven-inch guns were mounted in the stern on the main deck, also as chase guns.
The nine-inch gun was credited with the ability to penetrate of wrought iron armour at the muzzle. The eight-inch gun could penetrate of armour and the seven-inch gun could penetrate .
Northumberland was partially rearmed in 1875 with an armament of 7 nine-inch guns, 4 on the main deck, 2 forward chase guns and 1 rear chase gun. Two eight-inch guns replaced the seven-inchers on the main deck at the stern; the other 18 eight-inch guns remained where they were. In 1886 two breech-loading guns replaced two eight-inch guns. Six quick-firing (QF) 4.7-inch (120-mm) guns, 10 QF 3-pounder Hotchkiss guns, and six machine guns were later added.
Armour
Unlike her half-sisters, the entire side of Northumberlands hull was not covered with wrought iron armour. To compensate for the additional weight of her armament, only her battery was protected above the main deck. The ship was fitted with a complete waterline armour belt that tapered from at the ends to amidships. The armour extended below the waterline. The sides of the battery were long and it was protected by 5.5-inch armour on all sides, including transverse bulkheads fore and aft of the guns. The two forward chase guns on the upper deck were also protected by armoured bulkheads, but the stern chase guns on that same deck were entirely unprotected. The armour was backed by of teak. The ship also had a conning tower protected by 4.5-inch armour plates.