as heavily armoured as later Japanese capital ships. Nevertheless, the Kongō class possessed significant quantities of armour, and were heavily upgraded during their modernizations. In their initial configuration, the Kongō class possessed an upper belt that was thick, and a lower belt with a thickness of . Vickers Cemented was used in the construction of the Kongō, while the original armour of the other three was constructed of a variation of Krupp Cemented Armour, designed by the German Krupp Arms Works. Subsequent developments of Japanese armour technology relied upon a hybrid design of the two variations until drastic changes were made during the design of the Yamato class battleship in 1938. The armoured belt near the bow and stern of the vessels was strengthened with an additional of cemented armour. The conning tower of the Kongō class was very heavily armoured, with variations of Krupp Cemented Armour up to thick. The turrets were lightly armoured compared to later designs, with a maximum plate thickness of . The deck armour ranged from . During the reconstructions that each ship underwent during the interwar period, most of the armour of the Kongō class was heavily upgraded. The main lower belt was strengthened to be a uniform thickness of 8 inches, while diagonal bulkheads of a depth ranging from reinforced the main armoured belt. The upper belt remained unchanged, but was closed by 9-inch bulkheads at the bow and stern of the ships. The turret armour was strengthened to , while were added to portions of the deck armour. The armour upgrades increased the displacement by close to 4,000 tons on each ship, violating the terms of the Washington Treaty. Even after these modifications, the armour capacity of the Kongō class remained much less than that of newer capital ships, a factor which played a major role in the sinking of Hiei and Kirishima at the hands of U.S. Navy cruisers and battleships in 1942. Ships Due to a lack of available slipways, the latter two were the first Japanese warships to be built by Japanese private shipyards. Completed by 1915, they were considered the first modern battlecruisers of the Imperial Japanese Navy. According to naval historian Robert Jackson, they "outclassed all other contemporary [capital] ships". The design was so successful that the construction of the fourth battlecruiser of the British Lion-class——was halted so that design features of the Kongō class could be