Editing Battlecruiser (section)

===Plans in the aftermath of World War I===

''Hood'', launched in 1918, was the last World War I battlecruiser to be completed. Owing to lessons from Jutland, the ship was modified during construction; the thickness of her belt armour was increased by an average of 50 percent and extended substantially, she was given heavier deck armour, and the protection of her magazines was improved to guard against the ignition of ammunition. This was hoped to be capable of resisting her own weapons—the classic measure of a "balanced" battleship. ''Hood'' was the largest ship in the Royal Navy when completed; because of her great displacement, in theory she combined the firepower and armour of a battleship with the speed of a battlecruiser, causing some to refer to her as a fast battleship. However, her protection was markedly less than that of the British battleships built immediately after World War I, the {{sclass|Nelson|battleship|4}}.<ref name="Breyer, p. 168"/>

[[File:Lexington class battlecruiser2.jpg|thumb|left|''Lexington''-class battlecruiser (painting, c. 1919)]]
The navies of Japan and the United States, not being affected immediately by the war, had time to develop new heavy {{convert|16|in|mm|adj=on}} guns for their latest designs and to refine their battlecruiser designs in light of combat experience in Europe. The Imperial Japanese Navy began four {{sclass|Amagi|battlecruiser|2}}s. These vessels would have been of unprecedented size and power, as fast and well armoured as ''Hood'' whilst carrying a main battery of ten 16-inch guns, the most powerful armament ever proposed for a battlecruiser. They were, for all intents and purposes, fast battleships—the only differences between them and the {{sclass|Tosa|battleship|2}}s which were to precede them were {{convert|1|in|mm|adj=off}} less side armour and a {{convert|.25|kn}} increase in speed.<ref>Breyer, p. 353</ref> The United States Navy, which had worked on its battlecruiser designs since 1913 and watched the latest developments in this class with great care, responded with the {{sclass|Lexington|battlecruiser|4}}. If completed as planned, they would have been exceptionally fast and well armed with eight 16-inch guns, but carried armour little better than the ''Invincible''s—this after an {{convert|8000|LT|t|adj=on}} increase in protection following Jutland.<ref>Breyer, p. 234</ref> The final stage in the post-war battlecruiser race came with the British response to the ''Amagi'' and ''Lexington'' types: four {{convert|48000|LT|t|adj=on}} [[G3 battlecruiser]]s. Royal Navy documents of the period often described any battleship with a speed of over about {{convert|24|kn}} as a battlecruiser, regardless of the amount of protective armour, although the G3 was considered by most to be a well-balanced fast battleship.<ref>Gardiner & Gray, pp. 41–42</ref>

The Washington Naval Treaty meant that none of these designs came to fruition. Ships that had been started were either broken up on the [[slipway]] or converted to aircraft carriers. In Japan, ''Amagi'' and {{ship|Japanese aircraft carrier|Akagi||2}} were selected for conversion. ''Amagi'' was damaged beyond repair by the [[1923 Great Kantō earthquake]] and was broken up for [[ship breaking|scrap]]; the hull of one of the proposed ''Tosa''-class battleships, {{ship|Japanese aircraft carrier|Kaga||2}}, was converted in her stead.<ref>Gardiner & Gray, p. 235</ref> The United States Navy also converted two battlecruiser hulls into aircraft carriers in the wake of the Washington Treaty: {{USS|Lexington|CV-2|6}} and {{USS|Saratoga|CV-3|6}}, although this was only considered marginally preferable to scrapping the hulls outright (the remaining four: ''Constellation'', ''Ranger'', ''Constitution'' and ''United States'' were scrapped).<ref>Gardiner & Gray, p. 119</ref> In Britain, Fisher's "large light cruisers," were converted to carriers. ''Furious'' had already been partially converted during the war and ''Glorious'' and ''Courageous'' were similarly converted.<ref>Gardiner & Gray, p. 40</ref>