HMS Terror was an Erebus-class monitor built for the Royal Navy during the First World War in Belfast. Completed in 1916, she was assigned to the Dover Patrol where her primary duties involved bombarding German targets on the coast of occupied Belgium, particularly at the ports of Zeebrugge and Ostend. In October 1917 Terror was hit by three torpedoes, taking severe damage to the bow, and had to be towed into Portsmouth for repair. In April 1918 she participated in the Zeebrugge raid and provided gunnery support for the Fifth Battle of Ypres in September of the same year.

After the war the monitor was attached to HMS Excellent, the Royal Navy's gunnery school in Portsmouth and participated in gunnery trials in the 1920s. In January 1934 Terror became the base ship at Sembawang Naval Base in Singapore where she remained for the rest of the decade. From May 1939 to the end of the year she underwent an extensive refit in Singapore's dockyards.

After the outbreak of the Second World War and the completion of her refit, Terror was ordered home to Europe in January 1940. From early March, she served in the Mediterranean and defended Malta from Italian air raids before supporting the land-based assault of Italian positions in North Africa at the end of the year. In January 1941 the ship helped capture Bardia and Tobruk before attempting to defend Benghazi from German air attacks in February. After being damaged by two air attacks and two mines on 22 and 23 February, Terror was scuttled off the coast of Libya in the early hours of 24 February. The crew were evacuated to the minesweeper Fareham and corvette Salvia before she sank.

During the First World War, the Royal Navy developed several classes of ships which were designed to give close support to troops ashore through the use of naval bombardment. Termed monitors, they owed little to the monitors of the 19th century, though they shared the characteristics of poor seaworthiness, shallow draught and heavy armament in turrets. The size of the various monitor classes of the Royal Navy and their armaments varied greatly. The Marshal Ney class was the United Kingdom's first attempt at a monitor carrying 15 in (381 mm) guns. Following construction of the first two of the Marshal Ney-class, another four were ordered in May 1915, with the Harland and Wolff shipyard at Govan receiving a contract to construct two hulls, which were given yard numbers 492 and 493. However, all four were cancelled in June when it was realised that there were insufficient gun turrets to complete both the battleship, Royal Oak, and the monitors before 1917.

By August 1915, Marshal Ney, the first of her class, had revealed a very poor performance in her sea trials. The monitor's engines would not start reliably and were prone to stalling, making it impossible for the ship to achieve even the minimum standard for the trial of four hours of continuous sailing at full power. The vessel was also difficult to steer. Disappointed by the failure, the Admiralty began the design of a replacement class on 6 September, which incorporated lessons learned from all of the previous classes of monitor commissioned during the war. Some of the main modifications were an increase in the power supply to guarantee a speed of 12 knots (22 km/h; 14 mph) and a change to the angles and lines of the hull to improve steering. Another significant change was to raise the top of the anti-torpedo bulge above the waterline and reduce its width; both changes would improve the stability and maneuverability of the ship at sea. The bulge was fitted along each side of the ship and was intended to absorb the impact of any explosions. To maintain protection while reducing the bulge's width, its inner compartment was made water tight and filled with 70 steel tubes, rather than leaving the inner compartment open to the sea as in previous designs.

The new design, which would later be named the Erebus-class, was for a vessel 405 ft (123.4 m) long, 88 ft 2 in (26.9 m) wide with a draught of 11 ft 8 in (3.6 m). It would have 8,450 long tons (8,586 t) loaded displacement, with a maximum operational speed of 13 knots (24 km/h; 15 mph) produced by triple-expansion steam engines with two shafts, and a crew of 204. Power would be provided by four Babcock & Wilcox water-tube boilers, which would generate a combined 6,000 ihp (4,500 kW). The monitors would have an operational range of 2,480 nmi (4,590 km; 2,850 mi) at a speed of 12 knots.

The ships would be armoured to a similar standard to the Abercrombie class, which were launched in April 1915. Deck armour would range from 1 in (25 mm) on the forecastle, through 2 in (51 mm) on the upper deck and 4 in (102 mm) over the magazine and belt. With the main 15 in guns being originally intended for use on a battleship, the armour for the turret was substantially thicker than elsewhere in the design; with 13 in (330 mm) on the front, 11 in (279 mm) on the other sides and 5 in (127 mm) on the roof. The main gun's barbette would be protected by 8 in (203 mm) of armour. The conning tower was protected by 6 in (152 mm) of armour on the sides and 2.5 in (64 mm) on the roof. Each anti-torpedo bulge was 13 ft (4 m) wide with an outer air-filled compartment 9 ft (2.7 m) wide and an inner compartment 4 ft (1.2 m) wide containing the steel tubes.

Orders for two vessels of the new design were placed with Harland and Wolff on 29 September with reinstated yard numbers 492 and 493, which were renamed respectively Erebus and Terror on 13 October. Terror was laid down at Harland and Wolff's shipyard in Belfast on 26 October 1915 and launched on 18 May 1916.