||Naval Institute Press
- - - - - - download - - - - - -
Prior to the order in 1917 for the first purpose-built aircraft carrier, HMS Hermes, the Royal Navy had relied upon a motley collection of mercantile and naval conversions on which to launch (and occasionally land) aircraft. None of these ships embodied all - if any - of the essential elements of a genuine aircraft carrier, but all contributed in some way to the eventual development of such a vessel. During this same period the role of the aircraft at sea was also undergoing a transformation. Originally envisaged as a useful spotting device for relaying the fall of shot from a battleship's main armament, the aircraft was slowly gaining recognition as an effective striking force in its own right. The Washington Treaty of 1922 did much to stunt the development of new carriers by placing a limitation of 27,000 tons displacement per carrier, within a total tonnage of 135,000 tons for America and Britain and 81,000 tons for Japan. This limitation remained in force until the end of 1936. Each country was also permitted to convert two 33,000-ton capital ships into aircraft carriers. This additional provision suited the Royal Navy, which had a recognised requirement for five carriers and was thus able to convert the large light cruisers Courageous and Glorious into carriers during the latter half of the 1920s, in a similar fashion to HMS Furious (originally converted in 1917 and more extensively reworked between 1921 and 1925). A special clause in the Treaty enabled the USA to convert her two battlecruisers Lexington and Saratoga, which finally displaced 38,500 tons, under the pretext of permitting modifications to existing capital ships in order to protect them from underwater and air attack.