In 1904, as a result of the hostilities opened against Russia, Japan decided to launch an urgent shipbuilding program, among which were two battlecruisers of the Tsukuba class, baptized as Tsukuba and Ikoma. It was decided to arm these ships with four powerful 305mm guns, to be able to incorporate these ships to the “battle line” against the enemies and not only as escort of the battleships. They also had a good secondary artillery composed of 152 and 120mm guns and a protection, which was not much superior to that of previous Japanese armored cruisers, but it was more effective, since it was distributed in a different way and had new features such as installation of the belt based on Krupp cemented armor (KCA), more resistant than those used to date. They also had triple expansion steam boilers fueled by coal, which was sprayed with fuel oil to get more power. These ships were the first to be designed and built entirely in Japan, and when they entered service, they were considered the most powerful cruisers in the world, a title that they held until the arrival of the first British Battlecruisers. Their participation during the WWI was minimal, ending the conflict as training ships. The IJN Tsukuba sank in 1917 after an accidental explosion in one of its magazines and the IJN Ikoma was disarmed in 1922 to comply with the Washington Treaty.
TSUKUBA class gallery and more info