HMS Conqueror was an ironclad battleship of the Victorian Royal Navy, whose main armament was an armoured ram.

She was the first ship of the Conqueror class to be laid down, her only sister-ship being HMS Hero, which was completed some two years later. At the time of her design it was thought that ramming attacks were the most effective offensive manoeuvre against armoured warships, as the armour of the period was, for a short time, able to defend against the majority of contemporary guns extant. This belief was reinforced by the action at the battle of Lissa, when the Austrian battleship Ferdinand Max rammed and sank the Italian Re D'Italia. The Italian ship was at the time a stationary target, a detail which it appears did not receive, in naval architects' minds, the attention it deserved.

Conqueror was characterized as a steel armored turret ship and ram. Her length was 270 ft (82.3 m), beam was 53 ft (16.2 m), and draught was to be 23 ft (7.0 m). Displacement was estimated as 6,200 tons. The engines would develop 4,500 IHP, giving a speed of 13 knots.

Conqueror was innovative for being made of steel and using steel-faced iron armor (instead of only iron). The main belt was 12 inches thick at the waterline and 11 inches on the battery. The turret had armor of 12 to 14 inches in thickness. The deck armor was steel plating of 2-3 inches in thickness.

The new steel-faced iron armor was thought to be worth an additional 25% of iron armor. Which would mean that 12-14 inches of steel-faced armor were equivalent to 14-18 inches of iron armor.

Conqueror was also innovative for using breech-loading guns. The two main 12-inch (305-mm) calibre were placed in a turret and could fire over a clear upper deck from about 50 feet abaft the beam on one side to the same position on the other side. However, the guns were placed very near to the deck, and it was found that a discharge over the bow caused marked blast damage to the deck and associated fittings. Firing abaft the beam caused blast damage to the bridge and superstructure, so in practice the guns could only fire on the beam, through an arc of some 45 degrees. The heavy artillery was only intended to be used against a target which was on Conqueror's beam evading a ramming attack.^{[citation needed]}

Conqueror's main breech-loading guns were two BL 12-inch Mk II naval guns. They were of 12-inch (305-mm) calibre, and were 27.5 calibres (27.5 feet) long. They fired a shell weighing 714 pounds (324 kg) with a full charge of 295-pound (134 kg) of brown prismatic pulver. This resulted in a muzzle velocity of 1,910 ft/second (582 m/second). At this velocity, they could penetrate 10 inches (254 mm) of armour if the shell struck at or near a ninety-degree angle; much less, however, in the much more likely event of an oblique impact.

However that might be, the Mark II gun suffered from very severe production problems. By October 1884, the guns for Conqueror were expected to be finally ready by January 1885. Collingwood (1882) had four of the same guns mounted 'en barbette' and successfully tested her front guns in March 1885. Over a year later, in May 1886, she then tested her aft guns. With a reduced charge, one of these burst on the first shot.