Built under the Maru-1 Naval Armaments Supplement Programme, the "Mogami"-class cruisers were designed to the maximum limits allowed by the Washington Naval Treaty, using the latest technology. This resulted in the choice of the dual purpose (DP) 15.5 cm/60 3rd Year Type naval guns as the main battery in five triple turrets capable of 55° elevation. These were the first Japanese cruisers with triple turrets. Secondary armament included eight 12.7 cm/40 Type 89 naval guns in four twin turrets, and 24 Type 93 Long Lance torpedoes in four rotating quadruple mounts.