The Formidable-class ships were developments of earlier British battleships, featuring the same battery of four 12-inch (305 mm) guns—albeit more powerful 40-calibre versions—and top speed of 19 knots (35 km/h; 22 mph) of the preceding Canopus class, while adopting heavier armour protection.

By now rendered obsolete by the emergence of the dreadnought class ships, she was assigned to the 5th Battle Squadron and attached to the Home Fleet in 1912.

In late May 1915, she was withdrawn to reinforce the Italian fleet at the southern end of the Adriatic Sea after Italy joined the war on the side of the Allies.

The Formidable-class ships were powered by a pair of 3-cylinder triple-expansion engines that drove two screws, with steam provided by twenty Belleville boilers.

[6] In June 1902 she was in Alexandria for the scheduled coronation festivities for King Edward VII,[7] and in September that year she visited Nauplia in the Aegean Sea for combined manoeuvres with the Mediterranean and Channel squadrons.

In November 1902 she was Genoa to land Prince Louis on his departure home, and the officers of the ship attended the deferred coronation ball organized by the British colony in the city.

A flotilla of destroyers and monitors helped to break up the attack before Implacable and Queen arrived, but reports of an imminent German counterattack with armoured cruisers, which ultimately failed to materialize, led the British to send the battleships to guard against it in company with the Harwich Force.

On 14 November 1914, the 5th Battle Squadron was transferred to Sheerness in case of a possible German invasion attempt, but it returned to Portland on 30 December 1914.

By the end of the month, only Implacable, Queen, and their sisters Prince of Wales and London, along with the light cruisers Topaze and Diamond that had been assigned to support the 5th Squadron, were still at Portland.

By the time they arrived, the British had lost two battleships in the 18 March attack, prompting the Admiralty to send the last two ships of the 5th Squadron to join the fleet.

[17][18] Late in the day on 23 April, the Allied forces began to move into position for the landing; troop transports made their way to the concentration point off Tenedos.

On the night of 24–25 April, soldiers transferred from the troopships to Implacable, Cornwallis, and Euryalus, which then steamed to their landing beaches under cover of darkness.

Implacable arrived off X Beach, part of the landings at Cape Helles, and started sending men ashore at 04:00 under cover of her own bombardment of Ottoman defences.

In recognition of the critical support she had provided the troops as they attacked Ottoman positions, they named the landing site "Implacable Beach".

Based at Salonika, this squadron was organised to reinforce the Suez Canal Patrol and assist the French Navy in blockading the Aegean coasts of Greece and Bulgaria.

[17] In July 1917, Implacable returned to the United Kingdom and paid off at Portsmouth to provide crews for anti-submarine vessels,[17] and four main-deck casemates on either side were replaced by two 6-inch guns on her battery deck.