J3 battlecruiser

In 1916 the US had declared its intention to create a Navy "second to none"; Congress had authorized the building of a large number of battleships and battlecruisers. In response, the Japanese government also began a large programme of warship building (the 8-8 fleet). Two improved hulls were rebuilt into the two s by the Royal Navy during the war. The only new capital ships laid down during the war were the s. Their design had been called into question after the Battle of Jutland in 1916, and three ships of this class were cancelled, leaving only to be completed to a modified design. The US plan had been delayed by the wartime need to build smaller vessels. Nevertheless, estimates by the Admiralty were that by the early 1920s the Royal Navy would be behind in ships. The Japanese had finished one battleship since the end of the war and had three more under construction. To respond to this state of affairs, the Admiralty initially planned to build three battleships and one battlecruiser in the fiscal year 1921–22 and again in 1922–23, but this was changed to four battlecruisers to be built first, presumably to be followed by the same number of battleships the following year. The first two design proposals, 'K2' and 'K3', had a general layout similar to Hood, but were armed with either eight or nine 18-inch guns, in four twin or three triple gun turrets, respectively. The numeral in the designation came from the number of guns in each turret. These ships were very large, displacing , could only reach , and could only be docked in a single ex-German floating dock, and one dock, Gladstone Dock in Liverpool. The 'J3', the next proposal, saved nearly by reducing the main armament to nine 50-calibres long guns and the main deck armour to . Total armour was less than Hood but with increased power was expected to reach 32 kn. This reduction in size allowed the ship to dock anywhere that Hood could, and to pass through the Suez and Panama Canals. The configuration was considered poorly armoured and a more compact design I3 - with machinery aft, magazines centrally disposed and the main armament forward - was drawn up by the DNC and presented in late 1920. A variation of I3, the G3 design, with reduced gun calibre and thinner armour over machinery, was tendered as a means to reduce weight and hence increase speed. ==General characteristics==

The J3 battlecruisers were of very similar size to the Admiral class. They had an overall length of , a beam of , and a draught of at deep load. They would have displaced normally and at deep load, over more than the older ships. The main benefit of the design was a reduction in the weight of the main armament but increase in firepower by converting from twin to triple mount turrets, with the additional weight savings being used to improve protection and armouring. Propulsion The J3 battlecruiser design had four geared steam turbine sets, each driving one propeller shaft, and arranged in two engine rooms. The forward engine room held the two turbines for the wing shafts, while the aft engine room contained the turbine for the port and starboard inner shafts. The turbines were powered by 18 Yarrow small-tube boilers divided between nine boiler rooms. They were designed to produce a total of at a working pressure of and temperature of with superheat. Maximum speed would have been . Armament Housing the main armament in triple turrets was new to the Royal Navy, though British companies had been involved in the production of triple gun turret designs for other navies. The choice of a high muzzle velocity with a lighter shell was taken from the German practice; it ran counter to previous British guns such as the BL 15-inch Mark I gun which were lower-muzzle-velocity weapons firing heavy shells. The J3 design mounted nine 15-inch 50-calibre guns in three triple hydraulically powered Mark I gun turrets, designated 'A', 'B', and 'Z' from front to rear. The guns could be depressed to −3° and elevated to 40°. The ships' maximum stowage was 116 shells per gun. They fired projectiles at a muzzle velocity of . Their maximum range was about at maximum elevation. These weapons would have been very similar in construction to the BL 16-inch Mark I produced for the Nelson- class battleships The J3s carried a secondary armament of 12 BL 6-inch Mark XXII guns in twin turrets amidships behind the main bridge structure and ahead of the Z turret. The guns could elevate between –5° and +60°. An anti-aircraft battery of six QF 4.7-inch guns was included. A maximum of 256 rounds per gun could be carried. The ships were intended to carry four eight-barreled mountings for the QF 2-pounder gun (commonly known as a "pom-pom"), two abaft the funnels and two at the stern. Each gun would be provided with 1,300 rounds of ammunition. ==Notes==