was the lead ship in the four-vessel of heavy cruisers in the Imperial Japanese Navy. She was named after the Mogami River in Tōhoku region of Japan. The Mogami-class ships were constructed as "light cruisers" (per the London Naval Treaty) with five triple 155 mm dual purpose guns. They were exceptionally large for light cruisers, and the barbettes for the main battery were designed for quick refitting with twin 8-inch guns. In 1937 all four ships were "converted" to heavy cruisers in this fashion. Mogami served in numerous combat engagements in World War II, until she was sunk at the Battle of Leyte Gulf in October 1944. Background and design 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 triple mounts. To save weight, electric welding was used, as was aluminum in the superstructure, and a single funnel stack. New geared impulse turbine engines, driving four shafts with three-bladed propellers gave a top speed of , which was better than most contemporary cruiser designs and the Mogami class had twin balanced rudders, rather than the single rudder of previous Japanese cruiser designs. The class was designed from the start to be upgraded into heavy cruisers with the replacement of their main battery with 20 cm/50 3rd Year Type naval guns in twin turrets. However, in initial trials in 1935, Mogami and were plagued with technical problems due to their untested equipment, welding defects, and also proved to be top-heavy with stability problems in heavy weather. Both vessels, and their yet-to-be-completed sisters, and underwent a complete and very costly rebuilding program. Once rebuilt, the design, with its very high speed, armor protection, and heavy armament was among the best in the world during World War II. Service career Early career Mogami was laid down on 27 October 1931, launched on 14 March 1934 and completed at Kure Naval Arsenal on 28 July 1935. Her first captain was Captain Tomoshige Samejima, formerly