Actually, as built, the Mogami class were 6” gunned light cruisers, with a main battery of five triple Six Inch Gun turrets. In the late 30’s they were upgunned to 8” heavy cruisers, with the triple 6” turrets being replaced by twin 8” gun turrets. Light cruisers and heavy cruisers were differentiated by their main battery armament. 6” guns and smaller were classified as light cruisers by international treaty. Those with 7” or above were classified as heavy cruisers.BlackSheep214 wrote:Originally the Mogami was classified as a heavy cruiser with five main gun turrents - 3 in front, 2 in the rear before converting to an aircraft carrying cruiser later during WW2.
Mogami was converted to the float plane configuration after the severe damage she took at Midway, where her sister ship Mikuma was sunk. The two other cruisers of the class that were also present at Midway, Kumano and Suzuya, stayed in their five turret 8” gun configuration for the rest of their service lives until sunk later in the war.