The were a pair of dreadnought battleships built for the Imperial Japanese Navy (IJN) during World War I. Both ships carried supplies for the survivors of the Great Kantō earthquake in 1923. They were modernized in 1934–1937 with improvements to their armour and machinery and a rebuilt superstructure in the pagoda mast style. Afterwards they played a minor role in the Second Sino-Japanese War.

Despite the expensive reconstructions, both vessels were considered obsolete by the eve of the Pacific War, and neither saw significant action in the early years of the war. Following the loss of most of the IJN's large aircraft carriers during the Battle of Midway in mid-1942, they were rebuilt with a flight deck replacing the rear pair of gun turrets to give them the ability to operate an air group of floatplanes. A lack of aircraft and qualified pilots, however, meant that they never actually operated their aircraft in combat. While awaiting their air group, the sister ships were occasionally used to ferry troops and material to Japanese bases. They participated in the Battle off Cape Engaño in late 1944, where they decoyed the American carrier fleet supporting the invasion of Leyte away from the landing beaches. Afterwards both ships were transferred to Southeast Asia; in early 1945 they participated in Operation Kita, where they transported petrol and other strategic materials to Japan. The sisters were then reduced to reserve until they were sunk during American airstrikes in July. After the war they were scrapped in 1946–1947.

Background

thumb|left|[[Office of Naval Intelligence recognition drawing]]

The design of the Ise-class battleships was shaped both by the ongoing international naval arms race and a desire among Japanese naval planners to maintain a fleet of capital ships powerful enough to defeat the United States Navy in an encounter in Japanese territorial waters. The IJN's fleet of battleships had proven highly successful in 1905, the last year of the Russo-Japanese War, which culminated in the destruction of the Russian Second and Third Pacific Squadrons at the Battle of Tsushima.

In the aftermath, the Japanese Empire immediately turned its focus to the two remaining rivals for imperial dominance in the Pacific Ocean: Britain and the United States. This ratio, Satō theorized, would enable the Imperial Japanese Navy to defeat the US Navy in one major battle in Japanese waters in any eventual conflict. This was the genesis of the Eight-Eight Fleet Program, the development of a cohesive battle line of sixteen capital ships.

The launch of in 1906 by the Royal Navy raised the stakes, and complicated Japan's plans. Displacing and armed with ten guns, Dreadnought rendered all existing battleships obsolete by comparison. The launch of the battlecruiser the following year was a further setback for Japan's quest for parity. When the two new s and two armoured cruisers, launched by 1911, were outclassed by their British counterparts, the Eight-Eight Fleet Program was restarted.

The first battleships built for the renewed Eight-Eight Fleet Program were the two dreadnoughts of the , ordered in 1907 and laid down in 1908. In 1910, the Navy put forward a request to the Diet (parliament) to secure funding for the entirety of the program at once. Because of economic constraints, only four battlecruisers and a single battleship of the Fusō class were ultimately approved by the Diet. Three more Fusō-class ships (, , and ) were approved and all three were ordered in April 1913. While Yamashiro was laid down later that year, the IJN lacked the funding to proceed with the construction of Ise and Hyūga until the Diet authorized additional funding for the ships in July 1914.

Design and description

thumb|left|Ise underway during the 1920s

The progress of Fusōs construction, while the IJN waited for the funding to be released and foreign developments, caused the IJN to reassess the Fusō-class design. The distribution of the midships gun turrets was the most obvious flaw as they complicated the protection of the midships magazine and exposed more of the ship to the blast effects of the guns when they fired. Another issue was that Japanese sailors had problems maintaining a high rate of fire with the shells used in the manually loaded secondary guns used in the Fusō class and earlier designs. To resolve this issue, the IJN designed a smaller gun that offset its lighter shell weight with a higher rate of fire. It also decided that the barbette armour of the earlier ships was too thin and wanted a modest increase in speed to partially counter the higher speeds of the latest foreign ships like the British s and Russian s. For financial reasons more powerful engines could not be ordered so the new design was lengthened slightly and the boiler rooms enlarged to increase speed by to . To save weight the forecastle deck was shortened so that the lower midships gun turret was lower than in the Fusō class. This reduced the crew's accommodations despite a significant increase in the crew's numbers and naval historian Fukui Shizuo believed that these ships had the worst habitability of any Japanese capital ship. The final design was designated A-92 by the IJN.

The ships had a length of overall, a beam of and a draught of at deep load. They displaced at normal load and at deep load, roughly more than the preceding class. Their crew consisted of 1,360 officers and enlisted men. They had a metacentric height of at deep load.

During the ships' modernization during the 1930s, their forward superstructures were enlarged with multiple platforms added to their tripod foremasts. Both ships were also given torpedo bulges to improve their underwater protection and to compensate for the weight of the additional armour. In addition, their sterns were lengthened by . These changes increased their overall length to , their beam to and their draft to . Their displacement increased over to at deep load. The crew now numbered 1,376 officers and enlisted men. Each of the boilers consumed a mixture of coal and oil and the ships had a stowage capacity of of coal and of fuel oil, which gave them a range of at a speed of . Ise and Hyūga had three generators of capacity and two turbo generators at 225 volts.

During their 1930s modernization, the boilers on each ship were replaced by eight new Kampon oil-fired boilers, fitted into the former aft boiler room, and the forward funnel was removed. except for No. 6 turret as its supporting structure could not be lowered. The recoil mechanism of the guns was also changed from a hydraulic to a pneumatic system, which allowed for a faster firing cycle of the main guns.

By World War II, the guns used Type 91 armour-piercing, capped shells. Each of these shells weighed and was fired at a muzzle velocity of . They had a maximum range of at +20 degrees of elevation and at +43 degrees after modernization. Also available was a high-explosive shell that had a muzzle velocity of . A special Type 3 Sanshikidan incendiary shrapnel shell was developed in the 1930s for anti-aircraft use.

The ships' secondary armament consisted of twenty 50-calibre Type 3 guns. Eighteen of these were mounted in casemates in the forecastle and superstructure and the remaining pair were mounted on the deck above them and protected by gun shields. They had a maximum elevation of +20 degrees which gave them a range of . Each gun had a rate of fire of up to 10 rounds per minute. Anti-aircraft defence was provided by four 40-calibre 3rd Year Type 8-centimetre