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.

[1] To save weight and improve transverse stability, the class was given a more compact and lower superstructure, made of aluminium, which was welded rather than riveted.

Hull bulges were retrofitted to Mogami and Mikuma, and added to Kumano and Suzuya, increasing beam to 20.5 m (67 ft) and displacement to 11,200 tons, cutting speed by 2 knots (3.7 km/h; 2.3 mph).

Mogami and Mikuma were present at the Battle of Sunda Strait and contributed to the sinkings of the cruisers HMAS Perth and USS Houston.

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).

Mogami, heavily damaged by a collision with the cruiser Nachi, cruiser gunfire, and aerial attack, was scuttled by the destroyer Akebono, while Kumano limped into Manila harbor on one boiler, to be sunk by Halsey's aviators on 25 November 1944; the US escort carrier planes mauled Suzuya at Leyte, which was scuttled by the destroyer Okinami on 25 October.