The Courageous class consisted of three battlecruisers known as "large light cruisers" built for the Royal Navy during the First World War.

To maximize their speed, the Courageous-class battlecruisers were the first capital ships of the Royal Navy to use geared steam turbines and small-tube boilers.

They participated in the Second Battle of Heligoland Bight in November 1917 and were present when the High Seas Fleet surrendered a year later.

The first two Courageous-class battlecruisers were designed in 1915 to meet a set of requirements laid down by the First Sea Lord, Admiral Fisher, with his Baltic Project in mind.

The Director of Naval Construction (DNC), Sir Eustace Tennyson-d'Eyncourt, responded on 23 February 1915 with a smaller version of the Renown-class battlecruisers with one less gun turret and reduced armour protection.

The two ships were laid down a few months later under a veil of secrecy, so they became known in the Royal Navy as "Lord Fisher's hush-hush cruisers" and their odd design also earned them the nickname of the Outrageous class.

Gunnery experts criticized this decision because the long time between salvoes would make spotting corrections useless and reduce the rate of fire and thus the probability of a direct hit.

Admiral Fisher wrote in a letter to the DNC on 16 March 1915: "I've told the First Lord that the more that I consider the qualities of your design of the Big Light Battle Cruisers, the more that I am impressed by its exceeding excellence and simplicity—all the three vital requisites of gunpower, speed and draught so well balanced!

Fisher's adherence to this principle is highlighted in a letter he wrote to Churchill concerning the battleships of the 1912–13 Naval Estimates.

[5] To save weight and space the Courageous-class ships were the first large warships in the Royal Navy to have geared steam turbines and small-tube boilers despite the latter's significantly heavier maintenance requirements.

At full capacity, they could steam for an estimated 6,000 nautical miles (11,110 km; 6,900 mi) at a speed of 20 knots (37 km/h; 23 mph).

They fired 1,910-pound (866 kg) projectiles at a muzzle velocity of 2,575 ft/s (785 m/s); this provided a maximum range of 23,734 yd (21,702 m) with armour-piercing shells.

[9] The Courageous-class ships were designed with 18 BL 4-inch Mark IX guns, fitted in six triple mounts.

However, later testing proved that it was not deep enough to accomplish its task as it lacked the layers of empty and full compartments that were necessary to absorb the force of the explosion.

Water had entered the submerged torpedo room and rivets had sheared in the vertical flange of the angle iron securing the deck armour in place.

[27] Even as she was being built, Furious was modified with a large hangar capable of housing ten aircraft on her forecastle replacing the forward turret.

Admiral Beatty, commander of the Grand Fleet, ordered most of his light cruisers and destroyers to sea in an effort to locate the enemy ships.

[31] Two German Brummer-class light cruisers managed to slip through the gaps in the British patrols and destroyed a convoy headed to Scandinavia during the morning of 17 October, but no word was received of the engagement until that afternoon.

[33] The German ships, four light cruisers of II Scouting Force, eight destroyers, three divisions of minesweepers, eight Sperrbrechers (cork-filled trawlers, used to detonate mines without sinking) and two trawlers to mark the swept route, were spotted at 7:30 a.m.,[Note 2] silhouetted by the rising sun.

The British continued in pursuit, but lost track of most of the smaller ships in the smoke and concentrated fire on the light cruisers as opportunity permitted.

At 9:30 the 1st CS broke off their pursuit so they would not enter a minefield marked on their maps; the ships turned south, playing no further role in the battle.

[36] Courageous's mine fittings were removed after the battle and both ships received flying-off platforms on top of their turrets in 1918.

[26][39] Courageous was reduced to reserve at Rosyth on 1 February 1919 before being assigned to the Gunnery School at Devonport the following year as a turret drill ship.

Glorious was also reduced to reserve at Rosyth on 1 February and served as a turret-drill ship, but succeeded her sister as flagship between 1921 and 1922.

Their 15-inch turrets were placed into storage and later reused during the Second World War for HMS Vanguard, the Royal Navy's last battleship.

[42] Courageous became the first warship lost by the Royal Navy in the Second World War II when she was torpedoed in September 1939.

She participated in the Norwegian Campaign in 1940, but was sunk by the German battleships Scharnhorst and Gneisenau on 8 June 1940 in the North Sea.

[44] Furious spent the first months of the war hunting for German raiders and escorting convoys before she began to support British forces in Norway.

She spent most of 1940 in Norwegian waters making attacks on German installations and shipping, and most of 1941 ferrying aircraft to West Africa, Gibraltar and Malta before refitting in the United States.

Furious spent most of 1943 training with the Home Fleet, but made numerous air strikes against the Tirpitz and other targets in Norway in 1944.