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The 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. The ''Mogami''s 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. ==Design== 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 guns in five triple turrets (a first for Japan) in the ''Mogami''s, also capable of 55° elevation, making the ''Mogami''s 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.〔Lacroix, ''Japanese Cruisers'', pp. 434–435〕 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.〔Lacroix, ''Japanese Cruisers'', p. 438-439〕 Aiming to meet the weight limits compelled them to fit only ten boilers (compared to twelve in the previous and classes), trunked into a single funnel stack (which also saved tophamper). The new geared impulse turbines added over ''Atago'', increasing the top speed by . 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.〔Brown, ''Nelson to Vanguard'' p 74〕 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 and displacement to 11,200 tons, cutting speed by .〔Lacroix, ''Japanese Cruisers'', p. 439-442〕 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 .〔Lacroix, ''Japanese Cruisers'', p. 442-443〕 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 . The United States Navy's s were designed specifically to counter the ''Mogami'' class, and as a result had a very similar armament to the pre-refit ''Mogami''s, 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 s (1922–1926), this became the largest gun caliber allowed for light cruisers under the 1930 London Naval Treaty. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mogami-class cruiser」の詳細全文を読む スポンサード リンク
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