Mogami-class heavy cruiser

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The Mogami-class was composed of four vessels: Mogami, Mikuma, Suzuya and Kumano

The Mogami Heavy Cruiser

The Mikuma Heavy Cruiser

The Suzuya Heavy Cruiser

The Kumano Heavy Cruiser

Pre-War Plans

The Mogami-class (最上型) were a class of four warships built initially for the Imperial Japanese Navy (IJN Nihon Kaigun) as light cruisers in the early 1930s 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 caliber main armament and were reclassified as heavy cruisers.

For the 1931 Fleet Replenishment Program, believing themselves understrength in cruisers, the IJN chose to build to the maximum allowed by the Washington Naval Treaty. This resulted in a series of unique features:

(1) The choice of 155 mm (6.1 in) guns in five triple turrets (a first for Japan) in the Mogamis.

(2) They were also capable of 55° elevation, making the Mogamis one of the very few classes of cruiser to have a dual purpose (DP) main battery.

(3) They also had turreted torpedo launchers, also unique to the IJN.

Incidentally, the United States Navy’s Brooklyn-class cruisers were designed specifically to counter the Mogami-class, and as a result had a very similar armament to the pre-refitMogamis, in a nearly identical layout, though the US-pattern 6″/47 weapon was semi-automatic, with a higher rate of fire and the three weapons in each turret mounted in a single sleeve.

 why did they have design failures?

The IJN staff had a high degree (if not maximum) of interventionism in the design decisions. They required that a new class should have better performance than the existing classes or vessels in the same category. It posed under permanent stress the Japanese shipyard workers and designers. Furthermore, they were also limited by the Naval Treaties so they cannot always add or modify freely the ship features. Although the placement of Turret #3 improved its firing arc was a great innovation and the class had the stability problems fixed,  the Mogami-class were generally not considered an improvement over the Takao-class. Nonetheless, the follow-up Tone-class retained many aspects of the Mogami-class design. However, the Tones were intended for a different purpose, the long-search naval by airplanes. Therefore, all of their main armament forward, so their stern could accommodate additional float-planes.

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