Ibuki-class armored cruiser

The , also called the , was a ship class of two large armoured cruisers (''Sōkō jun'yōkan'') built for the Imperial Japanese Navy after the Russo-Japanese War of 1904–1905. These ships reflected Japanese experiences during that war as they were designed to fight side-by-side with battleships and were given an armament equal to, or superior to existing Japanese battleships. The development of the battlecruiser the year before was completed made her and her sister ship obsolete before they were completed because the foreign battlecruisers were much more heavily armed and faster.

Both ships played a small role in World War I as they unsuccessfully hunted for the German East Asia Squadron and the commerce-raider and protected troop convoys in the Pacific Ocean shortly after the war began. The ships were sold for scrap in 1923 in accordance with the terms of the Washington Naval Treaty.

Design and description

The ''Ibuki''-class ships were originally ordered during the Russo-Japanese War, on 31 January 1905, as armored cruisers. Before construction began, however, they were redesigned to incorporate guns in four twin turrets rather than the dozen guns in single mounts of the earlier ships. This required a larger hull to fit the turrets and thus more power from additional boilers to keep the same speed as the ''Tsukuba''-class ships.

These ships were given battleship-grade armament to overpower existing armored cruisers and were intended to fight in the battleline with battleships, much as had the two armored cruisers had done in the Battles of the Yellow Sea and Tsushima during the Russo-Japanese War. While more powerful than existing armored cruisers, the appearance of the British in 1908 with their armament of eight guns and speed of rendered these ships obsolete before they were commissioned. They were reclassified as battlecruisers in 1912.Preston, p. 194

The ships had an overall length of and a length between perpendiculars of , a beam of , and a normal draught of . They displaced at normal load and at full load, roughly more than the earlier ships.Itani, Lengerer & Rehm-Takahara, p. 54 The crew numbered about 845 officers and enlisted men.Jentschura, Jung & Mickel, p. 78 They had a metacentric height of .Itani, Lengerer & Rehm-Takahara, p. 57

Propulsion

Both ships were intended to be powered by vertical triple-expansion steam engines, but the long construction delays suffered by ''Ibuki'' made it possible for her to serve as a test-bed for the steam turbine. Four sets of Curtis turbines were ordered from the Fore River Shipbuilding Co., two each for ''Ibuki'' and the battleship . A month later, the Japanese paid $100,000 for a manufacturing license for the turbines.

''Ibuki'' was equipped with two turbine sets, each driving one shaft, which developed a total of , intended to give a maximum speed of . They used steam provided by 18 mixed-firing, superheater-equipped Miyabara water-tube boilers, with a working pressure of , that sprayed fuel oil on the coal to increase its burn rate. Performance during ''Ibuki''s initial sea trials on 12 August 1909 was unsatisfactory as she only reached despite the turbines exceeding their power rating with . The turbines were subsequently modified and the propellers were changed in an attempt to rectify the problem, but with only limited success. The ship ran her full-power trials again on 23 June 1910 and reached a speed of from .Itani, Lengerer & Rehm-Takahara, pp. 73, 76, 78

''Kurama'' used the traditional pair of four-cylinder reciprocating steam engines with a power rating of , more than the older ships. She used the same type of boiler as ''Ibuki'' and derived the additional power from the addition of four boilers, for a total of 28, which required an additional funnel. The ships carried a maximum of of coal and an additional of fuel oil although their range is unknown.

Armament

The ''Ibuki''-class armored cruisers were armed with four 45-caliber 12-inch 41st Year Type guns, mounted in twin-gun hydraulically powered centreline turrets. The guns had an elevation range of −3°/+23° and normally loaded their rounds at an angle of +5°, although loading at any angle up to +13° was theoretically possible. They fired projectiles at a muzzle velocity of ; this provided a maximum range of with armour-piercing (AP) shells. The intermediate armament was much heavier than the older ships, with four twin-gun turrets equipped with 45-calibre 8-inch 41st Year Type guns mounted on each side. The guns could be elevated to +30° which gave them a maximum range of around . Their projectiles were fired at a muzzle velocity of .

Defense against torpedo boats was mainly provided by fourteen 40-caliber 4.7-inch 41st Year Type quick-firing (QF) guns, all but two of which were mounted in casemates in the sides of the hull.Itani, Lengerer & Rehm-Takahara, p. 64 The gun fired a shell at a muzzle velocity of . The ships were also equipped with four 40-caliber 12-pounder 12 cwt QF guns"Cwt" is the abbreviation for hundredweight, 12 cwt referring to the weight of the gun. and four 23-caliber 12-pounder QF guns on high-angle mounts. Both of these guns fired shells with muzzle velocities of and respectively. In addition, the cruisers were fitted with three submerged torpedo tubes, one on each broadside and one in the stern. Each tube was provided with one training torpedo and two normal torpedoes.

Armor

Armor in the ''Ibuki'' class was improved compared to the earlier ships. The waterline armor belt of Krupp cemented armour was thick between the 12-inch gun turrets although it was only thick fore and aft of the turrets. Above it was a strake of armor that extended between the eight-inch gun turrets and protected the two central 4.7-inch casemates. In front of those turrets, the armor was thick. The ends of the main armor belt were connected to the main gun barbettes by transverse bulkheads.

The primary gun turrets were protected by armor plates thick and they had a roof. The armour for the eight-inch turrets was six inches thick. The main barbettes were protected by seven inches of armour and the secondary barbettes by five inches, although the armor for those thinned to behind the upper armor belt. The thickness of the armored decks was two inches throughout the ship. The sides of the forward conning tower were eight inches thick and its communications tube to the main deck was seven inches in thickness.

Ships

Construction and service

Construction of both ships was delayed by a lack of facilities at their shipyards, a shortage of appropriately trained workers and their low priority for building. ''Kurama''s lengthy building time at Yokosuka Naval Arsenal was due to priority given to the building of the battleships and and the repair and reconstruction of the ex-Russian ships captured after the Battle of Tsushima. ''Ibuki'' had to wait to have her keel laid until the slipway used by the battleship became available after ''Aki'' was launched. Kure Naval Arsenal took advantage of the delay with ''Ibuki'' to stockpile material and components and set a record between keel-laying and launching of five months, a figure only bettered by Portsmouth Naval Dockyard when they built the battleship in only four months. The decision to switch from reciprocating engines to turbines in ''Ibuki'' and ''Aki'' was not made until five days after ''Ibuki''s launching and thereafter she received priority over the battleship so that she was completed less than two years later, the first ship in the Imperial Japanese Navy to use steam turbines. In fact, construction on ''Aki'' was completely halted for about five months in favor of ''Ibuki'' because the former's turbines were late and the cruiser was better suited to serve as the testbed for the new technology.

''Ibuki'' sailed to Thailand in 1911 to represent Japan during the coronation ceremony of King Rama VI Vajiravudh.
When World War I began in August 1914, she was commanded by Captain Kanji Katō. The ship was ordered to Singapore and cooperated with the British to hunt down the light cruiser ''Emden'' in the East Indies and Indian Ocean. ''Ibuki'' was ordered to New Zealand to escort a large troop convoy of ANZAC troops to the Middle East in late September. She was ordered to guard the convoy, over Katō's protests, when the presence of the ''Emden'' was discovered in the Cocos Islands on 9 November. The Australian light cruiser HMAS ''Sydney'' was detached from the convoy to sink the ''Emden'' instead. With the ending of the threat to the convoy, ''Ibuki'' was transferred to the Second South Seas Squadron at Truk in the Caroline Islands.Corbett, p. 409 She was refitted at Kure in 1918, disarmed in 1922, and stricken from the Navy List the following year and scrapped in accordance with the Washington Naval Treaty. Her guns were turned over to the Imperial Japanese Army which emplaced one main-gun turret in the Tsugaru Strait between Honshu and Hokkaido and another in the Hōyo Strait in 1929.Gibbs, p. 217

''Kurama'' attended the Coronation Fleet Review of King George V in Spithead on 24 June 1911. She was at Yokosuka in August 1914 and was assigned to the 1st South Seas Squadron to search for the East Asia Squadron. They departed there on 14 September and reached Truk on 11 October as troops carried by the squadron occupied the Carolines.Sondhaus, p. 110 The squadron was based in Suva, Fiji in November in case the East Asia Squadron decided to double back into the Central Pacific. ''Kurama'' was flagship of the 2nd Squadron in 1917 and was transferred to the 5th Squadron the following year. Like her sister, she was disarmed in 1922, stricken in 1923 and subsequently scrapped. Two of her 203 mm turrets were subsequently emplaced as coastal artillery around Tokyo Bay.

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External links

New Japanese Armoured Cruiser ''Ibuki''
Contemporary discussion with specifications, photo & armor plan.
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{{Good article

Cruiser classes
Battlecruiser classes