The ships were designed as armoured frigates[Note 1] in response to an invasion scare sparked by the launch of the French ironclad Gloire and her three sisters in 1858.

In 1859 the Admiralty was not yet convinced that the very expensive (£377,000) Warrior-class ironclads,[1] which cost more than twice the wooden, steam-powered ships of the line,[2] had to be accepted as the norm.

They noted that the 4.5-inch (114 mm) 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.

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.

[1] 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.

The Defence class was 128 feet 8 inches (39.2 m) shorter overall and displaced more than 3,000 long tons (3,000 t) less than the Warrior-class ironclads.

The engines produced 2,329–2,343 indicated horsepower (1,737–1,747 kW) during sea trials which gave the ships maximum speeds of 11.23–11.4 knots (20.80–21.11 km/h; 12.92–13.12 mph).

They carried 450 long tons (460 t) of coal,[8] enough to steam 1,670 nautical miles (3,090 km; 1,920 mi) at 10 knots (19 km/h; 12 mph).

[21] The Defence-class ships had a wrought iron armour belt, 4.5 inches (114 mm) thick, that covered 140 feet (42.7 m) amidships.

[19] Transverse bulkheads 4.5 inches thick protected the guns on the main deck from raking fire.

[25] HMS Resistance was the first capital ship in the Royal Navy to be fitted with a ram and was given the nickname of Old Rammo.

The ship was sold for scrap in 1898 and foundered the following year en route to the breaker's yard.