The Mogami class
were four cruisers
built for the Imperial Japanese Navy
(IJN) during the 1930s. They were initially classified as light cruisers
under the weight and armament restrictions of the London Naval Treaty
. After Japan refused to comply any longer with that agreement, all four ships were rearmed with larger guns and were reclassified as heavy cruisers
. All four fought in World War II and were sunk.
s have been seen by naval architects as a design failure. The IJN's Naval staff insisted that each new class be superior to anything else in its category, yet designers strove to stay in compliance with treaty regulations. As a result, the initial construction of these ships was overly light; within their first few years of service, all four had to be reconstructed to remain seaworthy. They were also unstable seaboats due to excessive topweight and their welded seams cracked under the stress of firing their own main guns.
In June 1942, all four took part in the Battle of Midway, where Mogami and Mikuma collided trying to avoid a submarine attack; Mikuma was finished off on 6 June 1942 by aircraft from aircraft carriers USS Enterprise and Hornet. The heavily damaged Mogami limped home and spent ten months in yard, during which her afterparts were completely rebuilt, and "X" and "Y" turrets were replaced by a flight deck (with the intention to operate 11 aircraft).