HMS Furious was a modified Courageous-class battlecruiser built for the Royal Navy (RN) during the First World War. Designed to support the Baltic Project championed by the First Sea Lord, Lord Fisher, the ship was very lightly armoured and designed with a main battery of only two 18-inch guns. Furious was modified as an aircraft carrier while under construction. Her forward turret was removed and a flight deck was added in its place, such that aircraft had to manoeuvre around the superstructure to land. Later in the war, the ship had her rear turret removed and a second flight deck installed aft of the superstructure, but this was less than satisfactory due to air turbulence. Furious was briefly laid up after the war before she was reconstructed with a full-length flight deck in the early 1920s.

The Courageous class consisted of three battlecruisers known as "large light cruisers" built for the Royal Navy during the First World War. The class was nominally designed to support the Baltic Project, a plan by Admiral of the Fleet Lord Fisher that was intended to land troops on the German Baltic Coast. Ships of this class were fast but very lightly armoured, with only a few heavy guns. They were given a shallow draught, in part to allow them to operate in the shallow waters of the Baltic but also reflecting experience gained earlier in the 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.