The ship spent the war in the English Channel bombarding German positions along the Belgian coast as part of the Dover Patrol, often serving as a flagship.

Lord Clive was one of two ships in the class fitted with a single 18-inch (457 mm) gun in 1918, but she only fired four rounds from it in combat before the end of the war in November.

The director's crew would calculate the amount of traverse and elevation needed to hit the target and transmit that information to the turret for the guns to follow.

Two coal bunkers were turned into magazines for them, reducing the range to approximately 960 nmi (1,780 km; 1,100 mi), and increasing the crew in size to 215, necessitating plating in the sides of much of the upper deck to provide quarters.

The interior of the ship was extensively modified to accommodate the larger crew of 278 officers and men, storage and handling gear for the sixty 18-inch shells, and to support the weight of the gun mount.

Other changes included the transfer of the radio room down into the hold, the addition of a new gyrocompass, enlarging the bridge and rearranging the existing magazines and storage spaces.

[10] After Lord Clive finished working up she was sent to the Thames Estuary on 9 August 1915 to practice bombardment techniques with her sister ships Sir John Moore and Prince Rupert.

This had to be postponed for a day because of bad weather, but Lord Clive, her sisters and their supporting armada of ten destroyers, nine minesweepers, the seaplane carrier Riviera, four ships to handle the observation tripods, and no less than fifty drifters to handle the explosive anti-submarine nets laid to protect the monitors, sailed to a position about 10 miles (16 km) off Zeebrugge during the night of 22–23 August.

Lord Clive anchored and opened fire at 05:36 on the locks of the Zeebrugge Canal that led to the German naval base at Bruges, Belgium.

Vice-Admiral Reginald Bacon ordered the ships to cease-fire after two hours, cancelling the plans to bombard Ostend as well since both Sir John Moore and Prince Rupert had been suffering significant problems with their turrets.

The monitors returned in the afternoon when the haze cleared and Lord Clive opened fire at 15:30 with a ranging shot on the Ostende lighthouse.

The newly emplaced Tirpitz Battery of four long-range 283 mm (11 in) guns started to return fire and soon began to near-miss Lord Clive.

On the 25th Lord Clive and several other monitors bombarded German positions at Westende as part of a deception operation to suggest that the Allies were launching an attack in that sector.

This was the last bombardment for the next seven months as the monitors were used to support British light forces and the Dover Barrage, the complex of minefields and nets in the Channel.

This came in handy on 8 June when she, along with other monitors and destroyers, rebuffed an attempt by a dozen German ships to clear the nets and sweep the minefields.

[17] Lord Clive and all of the other monitors of the Dover Patrol simulated preparations for an amphibious landing during the later stages of the Battle of the Somme by firing on German positions at Westende between 8 and 15 September 1916.

[18] The monitor was nearby when a small group of German torpedo boats bombarded Dunkirk, France, during the night of 23/24 April 1917, and attempted to engage them in the darkness.

The ship and her sisters rehearsed their role up until mid-July when the battle began, but the Allies could not make the ten-mile (16 km) advance necessary to launch the operation.

Field Marshal Haig refused to support Bacon's proposal for a more modest landing in the Nieuport-Middelkerke area in September, so the operation was cancelled on 2 October.

She bombarded the Tirpitz and Aachen Batteries at Ostend, along with three other monitors, which fired fifty rounds between them during the abortive first attempt to block the Bruges–Ostend Canal that led to the naval base at Bruges on the night of 11 April.

The ship supported the Inshore Squadron making the landing attempt during the First Ostend Raid on 23 April with about fifty rounds of 12-inch and some 6-inch shells.