Mogami-class cruiser

The Mogami class (最上型) 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.

Class overview
Name: Mogami class
Operators:  Imperial Japanese Navy
Preceded by: Takao class
Succeeded by: Tone class
Built: 19311937
In commission: 19351944
Completed: 4
Lost: 4
General characteristics
Type: Heavy cruiser
Displacement: 8,500 tons (standard load) 10,980 tons (full load)
Length: 201.6 m (661 ft 5 in)
  • 20.6 m (67 ft 7 in) (Mogami class)
  • 20.2 m (66 ft 3 in) (Suzuya class)
Draft: 5.5 m (18 ft 1 in)
Installed power:
  • 152,000 shp (113,000 kW)
  • 8–10 Kampon boilers
Propulsion: 4 shafts; 4 geared steam turbines
Speed: 37 knots (69 km/h; 43 mph)
Range: 8,000 nmi (15,000 km; 9,200 mi) at 14 knots (26 km/h; 16 mph)
Complement: 850
  • Belt: 100 mm (3.9 in) (140 mm (5.5 in) over magazines)
  • Deck: 35 mm (1.4 in)
  • Turrets: 25 mm (0.98 in)
  • Magazines: 127 mm (5.0 in)
Aircraft carried: 3 × Aichi E13A reconnaissance floatplanes


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 the choice of 155 mm (6.1 in) guns in five triple turrets (a first for Japan) in the Mogamis, also capable of 55° elevation, making the Mogamis one of the very few classes of cruiser to have a dual purpose (DP) main battery; this was coupled with very heavy anti-aircraft protection, as well as the standard reloadable, turreted torpedo launchers, also unique to the IJN.[1]

To save weight and improve transverse stability, the class was given a more compact and lower superstructure, electric welding was used, as was aluminium in the superstructure.[2] Aiming to meet the weight limits compelled them to fit only ten boilers (compared to twelve in the previous Takao and Myōkō classes), and the chimney arrangement was designed to minimize weight as well; the middle funnel featured no chimney of its own, instead venting its exhaust gasses into the underside of the forward chimney, which itself was reclined from its base so that, at its top, it merged with the aft funnel's chimney. The new geared impulse turbines added 22,000 shaft horsepower (16,000 kW) over Atago, increasing the top speed by 1.5 knots (2.8 km/h). Protection, however, was not stinted on; the class proved able to take substantial punishment.

The declared weight was 8,500 tons, though the true design weight was 9,500 and at trials they would displace 11,169 tons.[3]

The designers, however, had overreached; excessive topweight led to instability, and gunnery trials revealed cracking hull welds. 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).[4]

Following Japan's withdrawal from the Second London Naval Treaty, plans were made to modernize and expand the entire fleet. Beginning in 1939, the class was brought in for substantial reconstruction, replacing the triple 155 mm turrets with twin 203 mm (8-inch) guns, turning over the 155 mm turrets for the battleships of the Yamato class.[5] Indeed, the designers had designed the class in mind so that the 6-inch guns could be switched with 8-inch batteries, in effect making them heavy cruisers and skirting the London Naval Treaty, though the Japanese had withdrawn from the conference and were not signatories to the Second London Naval Treaty of 1936.

Torpedo bulges were also added; in all, displacement rose to over 13,000 tons, and speed dropped to 34.5 knots (63.9 km/h).

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-refit Mogamis, in a nearly identical layout, though the US-pattern Mark 16/1 triple 6 in /47 Turret weapon was semi-automatic, with a higher rate of fire and the three weapons in each turret mounted in a single sleeve. Japan's choice of the 155 mm gun caliber is curious, as Japan already had a 6-inch (152 mm) weapon in service, of nearly equal performance. In spite of the resulting multiplicity of similar gun calibers, Japan resented the 5-5-3 treaty ratios, and had vowed to build to the very limit allowed by the 1922 Washington and 1930 London Naval Treaties. As the French had already used a 155 mm main battery in the three Duguay-Trouin-class cruisers (1922–1926), this became the largest gun caliber allowed for light cruisers under the 1930 London Naval Treaty.

War service

All four ships participated in the Japanese invasion of the Dutch East Indies. Mogami and Mikuma were present at the Battle of Sunda Strait and contributed to the sinkings of the cruisers HMAS Perth and USS Houston.

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).

In October 1944, the survivors were reunited at the Battle of Leyte Gulf. Mogami, heavily damaged by a collision with the cruiser Nachi, cruiser gunfire, and aerial attack, was scuttled by the destroyer 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; the US escort carrier planes mauled Suzuya at Leyte, and she was scuttled by the destroyer Okinami on 25 October.


This class is seen by naval architects as trying to fit a quart into a pint pot. The IJN's Naval staff insisted that each new class be superior to anything else in its category, which placed an enormous burden on Japanese naval constructors and the difficulties with these ships have to be seen in this light.

The initial construction was extremely light in order to comply with the naval treaties and had to be remedied. When the Royal Navy's Director of Naval Construction (DNC) was told about these ships by British Naval Intelligence, quoting the public displacement figure, he replied that the capabilities quoted could not be achieved on this displacement and that "they must be building their ships out of cardboard or lying".


Sub class Name Builder Laid Launched Completed Fate
Mogami Mogami (最上) Kure Naval Arsenal 27 October 1931 14 March 1934 28 July 1935 Scuttled after massive battle damage during the Battle of Surigao Strait on 25 October 1944
Mikuma (三隈) Mitsubishi Nagasaki Shipyard 24 December 1931 31 May 1934 29 August 1935 Sunk during the Battle of Midway on 5 June 1942
Suzuya Suzuya (鈴谷) Yokosuka Naval Arsenal 11 December 1933 20 November 1934 31 October 1937 Sunk during the Battle off Samar on 25 October 1944
Kumano (熊野) Kōbe-Kawasaki Shipbuilding Yard 5 April 1934 15 October 1936 31 October 1937 Sunk during the Philippine campaign on 25 November 1944 by aircraft of USS Ticonderoga


  1. Lacroix, Japanese Cruisers, pp. 434–435
  2. Lacroix, Japanese Cruisers, p. 438-439
  3. Brown, Nelson to Vanguard p 74
  4. Lacroix, Japanese Cruisers, p. 439-442
  5. Lacroix, Japanese Cruisers, p. 442-443


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