IJN Mogami

These ships win the prize for "Egregious Treaty Violation." The London Naval Treaty of 1930 (a follow-on to the Washington Naval Treaty of 1922) specified that cruisers of all signatory nations were to be held to displacements of 10,000 tons. Mogami, when first built, weighed in at about 13,400 (although I should also mention that some other Japanese CAs had been rebuilt by that point to exceed even this displacement). Not surprisingly, foreign naval observers were a little suspicious about her. Turns out that even given her extra displacement, she was overloaded. When she began running trials, it was discovered that firing all the guns of her main battery simultaneously had the unpleasant effect of popping the welds along her sides. Hmmm... When first launched, these ships were officially classified as light cruisers, because they were armed with 15 x 6" guns. They had been cleverly designed so that the turret base rings would also accept a dual 8" turret when the time came, and all were re-armed this way shortly before the war. Very sneaky...
At the battle of Midway, Mogami was very nearly sunk, and it was decided to rebuild her as an a hybrid cruiser/carrier to carry additional float planes. As you probably gathered from my comments on Ise and Hyuga, I'm not very impressed with this move, because none of these hybrid ships were very useful as aviation vessels. I find it ironic that Mogami's last action was to be sunk at the hands of the same U.S. battleships that sank Fuso andYamashiro in Surigao Strait. Apparently, she was useless enough as an aviation vessel that she wasn't even included in Ozawa's sacrificial carrier bait force, but was relegated to surface combat duty with the two oldest BBs in the Japanese Navy.

The Mogami-class (最上型^?) were a class of four warships built initially for theImperial Japanese Navy (IJN) as light cruisers in the early 1930s under the weight and armament restrictions of theLondon 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. All four fought in World War II, and were sunk.

The Mogamis 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.

Class overview
Operators:	Imperial Japanese Navy
Preceded by:	Takao-class cruiser
Succeeded by:	Tone-class cruiser
Built:	1931–1937
In commission:	1935–1944
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)
Beam:	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)
Propulsion:	Four-shaft impulse single geared turbines 10 Kampon boilers (Mogami-class) 8 Kampon boilers (Suzuya-class) 152,000 shp
Speed:	37 knots (43 mph; 69 km/h)
Range:	8,000 nmi (15,000 km) at 14 kn (16 mph; 26 km/h)
Complement:	850
Armament:	(initial) • 15 × 155 mm/60-cal guns (5×3) (replaced by 10 x 20 cm/50 3rd Year Type 2 guns (5x2) from 1939) • 8 × 127 mm (5.0 in)/40-cal DP guns (4×2) • 4 × 40 mm AA guns • 12 × 610 mm (24 in) torpedo tubes(4×3)
Armor:	Belt: 100 mm (3.9 in) Deck: 35 mm (1.4 in) Turrets: 25 mm (0.98 in) Magazines: 127 mm (5.0 in)
Aircraft carried:	3 × Aichi E16A reconnaissancefloatplanes

Design[edit]

For the 1931 Fleet Replenishment Program, believing themselves understrength in cruisers, the IJN chose to build to the maximum allowed by theWashington Naval Treaty. This resulted in the choice of 155 mm (6.1 in) guns in five triple turrets (a first for Japan) in theMogamis, 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 tubes, 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 Myoko classes), trunked into a single funnel stack (which also savedtophamper). The new impulse geared turbines added 22,000 shp 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 kt (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 battleship Yamato.^[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 kt (63.8 km/h).

The United States Navy's Brooklyn-class cruisers were designed specifically to counter theMogami-class, and as a result had a very similar armament to the pre-refit Mogamis, 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. Japan's choice of the 155mm gun caliber is curious, as Japan already had a 6" (152mm) 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 155mm 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[edit]

All four ships participated in the Japanese invasion of the Dutch East Indies. The Mogami andMikuma were present at the Battle of Sunda Strait and contributed to the sinkings of HMASPerth 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 fromUSS 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 Nachi, 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 byHalsey's aviators on 25 November 1944; the US escort carrier planes mauled Suzuya at Leyte, and she was scuttled by Okinami on 25 October.

Criticism[edit]

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, this 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".

Though the placement of Turret #3 improved its firing arc, and though the class had the stability problems fixed (the preceding Takao-class cruisers were considered too top-heavy), the Mogamis are generally not considered an improvement over the Takaos.^[6] Nonetheless, the follow-up Tone-class retained many aspects of the Mogami-class design. However, theTones were intended for a different purpose with all of their main armament forward, so their stern could accommodate extra floatplanes.

Ships[edit]

Sub class	Name	Builder	Laid	Launched	Completed	Fate
Mogami	Mogami(最上)	Kure Naval Arsenal	27 October 1931	14 March 1934	28 July 1935	Sunk during the Battle of Leyte Gulf 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 thePhilippine campaign on 25 November 1944 by aircraft of USSTiconderoga

IJN mogami in game forgotten hope

IJN Mogami, Yamashiro in Battle of the Surigao strait 1944.

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