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.

[2] Her hull was subdivided by 15 watertight transverse bulkheads and had a double bottom underneath the engine and boiler rooms.

It produced a total of 6,558 indicated horsepower (4,890 kW) during the ship's sea trials on 15 September 1868 and Northumberland had a maximum speed of 14.1 knots (26.1 km/h; 16.2 mph).

[11] The nine-inch gun was credited with the ability to penetrate 11.3 inches (287 mm) of wrought iron armour at the muzzle.

[13] Unlike her half-sisters, the entire side of Northumberland's hull was not covered with wrought iron armour.

She was altered while on the building slip after Sir Edward Reed succeeded Isaac Watts as Chief Constructor.

Unlike her half-sisters, the ship spent five years on the stocks before she was ready to be launched, partially due to frequent changes in design, although Northumberland was much closer to completion.

The additional weight caused her stick for an hour on the slipway before she slid halfway down with her stern only supported by air, threatening to buckle the ship.

During this time she helped her half-sister Agincourt tow a floating drydock from England to Madeira where it would be picked up by Warrior and Black Prince and taken to Bermuda.

The ships departed the Nore on 23 June 1869, loaded down with 500 long tons (510 t) of coal stowed in bags on their gun decks, and transferred the floating dock 11 days later after an uneventful voyage.

The ship was paid off in 1885 for another refit and became the flagship of Vice Admirals Sir William Hewett and John Baird, successive commanders of the Channel Squadron, upon her completion in 1887.

She struck her pennant on 31 March 1910, following the transfer of the second-class stokers berthed in her to Chatham Naval Barracks,[19] and thereafter served as a coal hulk at Invergordon, initially designated C.8, she was renamed C.68 in 1926.