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.