Mogami's keel was laid down at the Kure Navy Yard, Kure, Japan, in October 1931. She was launched March 1934 and completed July 1935.

For the 1931 Fleet Replenishment Program, believing themselves understrength in cruisers, IJN chose to build to the maximum allowed by the Washington Treaty. This resulted in the choice of 155 mm in five triple turrets (a first for Japan) in the Mogamis, also capable of 55° elevation, making Mogamis unique in having DP main battery; this was coupled with very heavy AA protection, as well as the standard reloadable turreted torpedo tubes, also unique to IJN.

To save weight, electric welding was used, as was aluminum in the superstructure. Weight compelled reduction to only ten boilers (compared to twelve in the previous Atago and Nachi classes), trunked into a single stack (which also saved tophamper). The new impulse geared turbines added 22,000 shp over Atago, increasing speed 1.5 kt (2.8 km/h). Protection, however, was not stinted on; the class proved able to take substantial punishment.

The designers, however, had overreached; excessive topweight led to instability, and gunnery trials revealed cracking hull welds. Hull bulges were retrofitted to Mogami, increasing beam to 19.2 m (63') and displacement to 11,200 tons, cutting speed 2 kt (3.7 km/h).

Beginning in 1939, Mogami and her sisters were brought in for substantial reconstruction, converting the triple 155 mm turrets to twin 203 mm (8'), turning over the 155 mm turrets to Yamato. Torpedo bulges were also added; in all, displacement rose to 12,400 tons, speed dropping to 34.5 kt (63.8 km/h).

[edit] History

Mogami and her sister ships attended at the Battle of Midway in June 1942, where Mogami and Mikuma collided trying to avoid a submarine attack. The pair was subsequently caught by American carrier aircraft; Mikuma was sunk but Mogami managed to limp home to spend ten months in yard. Her afterparts were completely rebuilt, 'X' and 'Y' turrets replaced by a flight deck (with the intention to operate 11 aircraft). The Ise-class battleships received similar 'carrier battleship' refits.

The surviving cruisers were reunited at the Battle of Leyte Gulf in October 1944. Mogami, heavily damaged by collision, cruiser gunfire and aerial attack, was scuttled by Akebono, while Kumano stumbled into Manila harbor on one boiler, to be put out of her misery by Halsey's aviators on 25 November 1944.