Before the Kongō class battlecruiser design was created, similar type of British ship construction had been studied thoroughly (Thunderer, Neptune, Lion and Indefatigable). During a council held on April 13, 1910, an order for new class of ships was discussed, but a final decision was not made until May 23, 1910. In December 1910, during the Parliament meeting, the Japanese Prime Minister Saitō proposed construction of, as he described them in his speech, “huge armoured cruisers” based on the British “Invincible” class.
According to the Prime Minister, in the first phase, a decision was made to order one ship from Great Britain, with initial displacement of 18,500 T, armed with eight 30 cm guns. Another ship, and perhaps an additional one, were to be built in Japan on the basis of the first ship’s design. Generally speaking, the requirements for the ship were not elaborate. It was to be a construction with armour, power plant and armament superior to its British-built counterpart. The requirements for the ships are presented by scheme in Table 1.
Later, other designs were created. The one designated B.45 (type II) called for a ship with initial dimensions 655’ x 93’ x 28; displacement of 26 500 T1 and 65,000 SHP. Three variants for different length were developed. The first calculations were made for a ship 660’ long, with 86,400 SHP engines; the second concerned a ship 663’ long, with 64,500 SHP engines; the third were made for a ship 685’ long, with 66,000 SHP engines. The estimated maximum speed was 27 knots. It is worth noting that on the basis of that design, a final one, designated B.46, was created. Further units of that class – Hiei, Haruna or Kirishima – were similar, but since they were built in Japanese shipyards, there was little difference between their final characteristics and those of the Kongō prototype.
It is worth remembering that the Kongō class battlecruiser design was strictly connected with two people. One of them was their main creator, Commodore Motoki Kondo. His professional career began in March 31, 1883, when he graduated from the engineering department of the Tokyo University. Three years later, Kondo went to Great Britain where he began maritime studies. Shortly after graduation on June 30, 1890, he returned to Japan. In the rank of lieutenant (technical), he began work in the construction office of the Yokosuka Shipyard. The knowledge he had acquired abroad presented him with a chance to be an academic teacher in the Tokyo University. His further career developed according to his personal expectations. In 1897, Kondo was promoted to constructor lieutenant commander and a year later, constructor commander. In 1902, he was promoted to the rank of constructor captain and began work in the Imperial Japanese Navy Technical Department (Kaigun Kansei Honbu). Commissioning of a British “Dreadnought” gave him an opportunity to go to Great Britain and have a closer look at the new battleship. After returning to Japan, on August 9, 1907, he started work in the 3rd Division of the Navy Technical Department, where he worked on new designs of Imperial ships. One of his first ones was the B 46 battlecruiser. After its completion, Kondo was promoted to the rank of constructor general (Zosen Sokan) on December 10, 1910. The other person connected with the Kongō design was Sir George Thurston responsible for adaptation of Japanese design requirements.
The contract for building the first of the four planned ships, was signed in December 1910. Cost of a single vessel construction was in initially estimated at 27,580,000 yen. Construction of the third in the series – battlecruiser Haruna – was commenced on March 16, 1912, in the Kawasaki Shipyard. The commissioning ceremony took place on April 19, 1915. The ship was classified as Soko Junyōkan No 2.
The battlecruiser’s hull had six main decks, two of which were above the armoured citadel and the other four were between the double bottom and the top armoured deck covering the citadel. The hull was divided by a longitudinal bulkhead running along the ship’s plane of symmetry. Because of that, the entire engine room was divided into two parallel sections. Between the engine room side bulkhead and the ship’s side, there were two rows of watertight compartments. The smaller, outer ones were empty while the inner ones, between the former and the engine room bulkhead, were filled with coal along the entire length of the boiler room. Their additional task was to protect the boiler and engine rooms against torpedoes and mines. Along with other watertight compartments placed in different parts of the ship, they guaranteed reserve buoyancy and increased the ship’s reserve displacement. Twenty watertight compartments divided the hull abeam. The crew quarters, magazines and main artillery turrets were located in the bow section. The boiler room was behind them, amidship. Eight watertight compartments housed coal-fired boilers supplying steam to the turbines. The main specifications of Haruna after her commissioning is presented in Table 2.
Armour above the water line.
Side armour of the Kongō class ships comprised several dozen, 203 mm armour plates, tightly connected together and bolted to the 16 mm side of the hull. The plates formed an armoured belt stretching from the A barbette of the main battery to the Y barbette. Individual segments of the armour plates were made of KC steel (Krupp Cemmented). The upper part of the main belt was placed directly on the bottom plate. Its thickness was constant at 152 mm. It was made of KC steel and installed directly to the 13 mm side plating made of NS steel (Nickel Steel). A third, 152 mm armoured belt, made of KC steel, was above it, mounted, as the latter one, to the 13 mm NS side plating. The bow section, at the water line, from the A turret to the stem and the stern section from the Y turret to the rudder shaft were covered with thinner, 76 mm armour, made of KC steel. Below the main belt, there was a narrow belt made of 76 mm KC steel, that formed a base for the lower edge of the main belt.
Horizontal armour on decks above the water line did not exist on the Kongō class ships. The sides of the battlecruiser’s hull were protected by three armoured belts placed one above the other. Only the upper deck provided horizontal protection for the ship. Individual segments of the deck were made of 38 mm NS steel plates and covered mainly the edges of the deck between the B and X barbettes, leaving part of the midship in the line of symmetry, unprotected.
Armour below the water line
Vertical protection system of the battlecruiser, below the water line, consisted of armour covering the ammunition magazines of the main artillery turrets. It was made of 12.7 to 19 mm NS steel. Horizontal armour of the decks was slightly better. The first platform deck was armoured in some areas. In the bow section, it was the torpedo room with a roof made of 38 mm NS steel. The bow side bulkhead was made of 127 mm KC steel. The artillery ammunition magazines’ floor was made of 25 mm NS steel, their sides were protected by a 19 mm NS bulkhead. Another ammunition magazine, behind the boiler room, had a 25 mm NS floor. Side bulkheads in that area were of various thickness. On the level of the first platform deck, they were partially made of 19 mm NS steel, a little higher – on the level of the lower deck – they were 12.7 mm thick (NS). The ammunition magazine below the Y turret barbette had identical armour – 25 mm NS floor, 19 mm NS bulkheads. Armour of the under deck (Ge Kanpan) was almost entirely made of 19 mm NS steel. The stern was an exception. The torpedo room was covered with 64 mm KC steel plates, the rudder engine room was protected by a 51 mm NS deck.
When the Kongō class battlecruisers entered service, they were equipped with standard propulsion designed for big units, comprising 2 turbines and 36 large boilers supplying heated steam. However, not all ships were fitted with the same turbines and boilers. The first three ships received the Parsons turbines. Haruna was the exception, since she was the only one of the four units to be equipped with the Brown-Curtiss turbines. As far as boilers are concerned, only Hiei was fitted with the I Kanpon boilers while the other battlecruisers were equipped with 36 boilers of the Yarrow type. Detailed data concerning the engine room before refit is presented in Table 3. After being rebuilt, the main changes concerned only boilers (Table 42). The battlecruisers were very manoeuvrable. During turning manoeuvre trials conducted by Haruna with displacement of 35.921 T at 35.92 knots and 29.6 degrees rudder deflection, after 820 m, the battlecruiser’s turning diameter was 953 m with 9.5 degrees heel. Kirishima at the speed of 28.56 knots and 30 degrees rudder deflection, after 871 m, reached a turning diameter of 826 m at 11.5 degrees heel.
In December of 1910, the Prime Minister, M. Saitō, informed the public of plans to build new ships with main armament comprising eight 12-inch guns. Initial scheme of the 1st type battlecruisers: B.39 – B.41 Kongō class is presented in Table 6.
As seen in the table above, the question of main armament was not entirely agreed upon and requirements concerning main artillery varied between 12 and 14 inches as they were based on solutions employed on HMS Thunderer, Neptune, Lion or Indefatigable. During the design development (B.42 – B.45), discussions concerning the ship’s dimensions and speed, pushed the matter of the main armament aside. Twelve-inch guns were to be fitted on the ship. The final design of Kongō, dated on May 13, 1910, confirmed the data. According to it, the main armament was to include eight 12-inch guns with the length of 50 calibres. They were to be mounted in two-gun turrets with an ammunition unit of 80 rounds per gun. The gun calibre was changed after a Japanese 14-inch (355.6 mm) gun construction had been approved on November 29, 1911. It was designated as 14 inch/45 calibres type 41 (45 Kōkei 41 Nendo Shiki 14 In Hō). The design was based on the British Vickers Mk J built in 19103. The Kongō prototype ship was armed with eight 14-inch guns (45 Kōkei Hi Shiki 36 cm Hō) Kai 1 mounted in the Hi Shiki type gun turret with a Hi Shiki type breech, made in the British Vickers factory. Technical data of the guns and gun turrets of that type are presented along with their modifications in Table 7. As the data shows, not all units of that class were equipped with identical and homogeneous armament. Changes introduced on Haruna are presented in Tables 8 and 9. The last ship of the class – Haruna – was armed with eight 36 cm guns (Kōkei 41 Shiki 36 cm Hō) Kai 3 mounted in the Hi Shiki type gun turrets but fitted with the 41 Shiki type breech. The guns were produced in the Kure arsenal.
During the entire period of service, the only guns mounted on all ships were the ones presented in the table. The issue of gun turrets was different. Kongō, right after her commissioning, was fitted with gun turrets manufactured by Vickers. During the ship’s modernization, they were replaced by new ones with higher elevation angle, which increased the guns’ range.
Medium artillery, after commissioning, comprised sixteen 15 cm guns mounted in casemates at midship, on both sides. The prototype Kongō was armed with homogeneous guns made by Vickers designated 50 Kōkei Hi Shiki 15 cm Hō. The other ships were equipped with Japanese guns designated 50 Kōkei 41 Shiki 15 cm Hō. Detailed specifications of both gun types is presented in Table 9. The construction of Japanese 15cm/50 calibres guns was based on the British Vickers model. It was introduced in 1914, as 41 Shiki and became part of the armament installed on the battlecruisers Hiei, Haruna and Kirisima.
The first Japanese anti-aircraft guns were developed on the basis of low elevation guns and turrets. The base design was a 7.62 cm 40 Kōkei 41 Shiki type gun, approved in 1915. Its maximum elevation angle was 75 degrees, which, at that time, was appropriate for that type of gun. A new design was accepted on February 5, 1916, designated 40 Kōkei 3 Nen Shiki Dai Gyōkaku hō4 (with high angle of elevation). For the first time, the gun was mounted on the battleship Yamashiro and later, on the Kongō class battlecruisers, battleship Fūso and the Ise class ships. The gun, designed by engineer C. Hada, was developed in 1914 and its prototype, after successful field trials, was approved to be mounted on all Japanese heavy ships. It was produced by the Kure Arsenal with cooperation of the Hiroshima Armament Factory. The person responsible for the construction was Cpt. M. Oyamada. During the first period of service, the gun proved to be very effective when engaging slowly moving aircraft at medium distance. However, with aircraft development, it needed to be replaced by a more modern type with higher ceiling and rate of fire. The prototype Kongō, after entering service, received 8 guns of that calibre, made by Vickers. Further ships, commissioned between 1914 and 1915, were equipped with only four type 41 Shiki Japanese guns. Specifications of both guns and their modifications are presented in Table 11. The short version of the gun, designated Tan5 8 cm Hō with length of 20 calibres, was also mounted on the battlecruisers. This time, Kongō received 4 guns made by Vickers, the other ships were armed with 8 guns of the Japanese type 41. Their specifications are presented in Table 12. The gun mount was designed by engineer C. Hada and produced by the arsenal in Maizuru, under supervision of Commander Hisasue. With time, the guns became outdated and did not meet the requirements for anti-aircraft armament, which was confirmed during gunnery exercise conducted by the battleships of the 1st Squadron in 1926. The guns achieved an average accuracy of 4.57% when firing at 10-meter targets flying at 110 km/h, with the ships’ constant speed of 15 knots. The poor results were also caused by lack of appropriate aerial target acquisition system. It is worth noting that the guns remained on the decks of the Japanese heavy units for a very long time, until the beginning of the war in 1941.
Guns designated as Kōkaku hō (with high elevation) were also mounted on Japanese battlecruisers and battleships. Their specifications and numbers of mounts on individual ships are presented in Table 13.
Contemporary 8 cm anti-aircraft guns had a limited range and ceiling. With dynamic development of naval aviation, in the late 1920s, they had to be replaced by more modern 12 cm calibre types. The decision to choose that calibre was forced by a trend that prevailed in the development of anti-aircraft artillery. The 8 cm gun was also marked by poor workmanship and unsatisfactory ballistic characteristics. While developing the new type of gun, engineers concentrated on replacing the breech, increasing shell weight and improving ballistic parameters. A prototype, presented by engineer Hata was tested and received positive assessment of Japanese specialists. It was introduced to the Japanese Navy under designation 45 Kōkei 10 Nen Shiki 12 cm Kōkaku hō. Its service was not long as significance of naval aviation and role of aircraft carriers increased. It forced the Imperial Navy to search for the most effective solutions for anti-aircraft protection. Th IJN followed the path paved by the navies of other countries and slightly increased the calibre of anti-aircraft guns. On the basis of the 12 cm gun in service, a new design of a 12.7 cm anti-aircraft gun was developed at the end of 1928. After three years of construction work, the navy arsenals in Kure and Hirosima built the first piece. Trials of the experimental gun began in 1931 and after their completion, the gun was approved on February 6, 1932 as type 89 Shiki, 12.7 cm calibre with 40 calibres length (40 Kōkei 89 Shiki 12.7 cm Kōkaku hō). The new gun was to form an aerial target acquisition system along with the type 91 targeting system that was simultaneously undergoing trials. The gunnery tests gave positive results and soon the new gun became standard armament of Japanese ships. The 12.7 cm gun was designed by engineer Chiyokichi Hada. It was produced in the arsenal in Kure with cooperation of the armament factory in Hiroshima. Turrets for the gun were manufactured by arsenals in Kure and Yokosuka.
Light anti-aircraft artillery
The 40 mm6 gun was bought in the Vickers factory (Mk VIII) in 1925 and underwent intensive testing in the Kure Naval Arsenal. After achieving positive results, the gun was approved and introduced into the navy weaponry. Its Japanese counterpart was constructed by Admiral F. Shimizu and manufactured in factories in Kure and Yokosuka under supervision of Shimizu himself. The gun was mounted on all battlecruisers and battleships. Detailed specifications and number of guns mounted on ships are presented in Table 15. During its service, the gun turned out to be difficult to operate as it demanded highly skilled personnel. That was why the navy began searching for different anti-aircraft types of gun to replace it. In the middle of 1935, a decision was made to rearm the ships with smaller calibre guns.
All heavy units of the Imperial Navy – fast battleships and battleships – were armed with standard 25 mm anti-aircraft artillery. Made by Hotchkiss, the gun was purchased in 1930 from France with designation 94 and 95 Shiki 25 mm Kijun. Until June 19, 1935, the gun was tested in Yokosuka. Decision to introduce a smaller calibre gun was caused by difficulties in operating 40 mm guns. Upon trials completion, the gun’s final version, slightly modified with help of specialists form the German Rheinmetall company, was designated 96 Shiki 25 mm Kiju 1 kata (Kiju – machine gun). A twin-barrel version was adopted on August 6, 1936, and introduced into production as 96 Shiki 25 mm Kiju 2 kata. Three-barrel mounts were approved in 1941 and single-barrel ones in 1943.
In the first period of the battleships service, only electrically powered, twin-barrel type 96 mark 2 gun turrets, designed by Rear Admiral K. Katsuta were used. The guns were produced in Toyokawa and Yokosuka under the supervision of Rear Admiral M. Hori. Target acquisition was provided by type 95 anti-aircraft gun directors. Ammunition included high explosive, tracer, incendiary and armour-piercing rounds. It was common to add a tracer to every four or five rounds for better trajectory observation. Eight feeders supplied rounds to ready-service ammunition boxes. There were 2,600 anti-aircraft rounds per gun and the immediate reserve, ready to be used, comprised 100 rounds. The air-cooled gun was fed from the top by 15-round magazines that provided theoretical rate of fire of 220 rounds per minute.
The twin-barrel mount was electrically powered, in three planes, by a system of two 1 hp motors. They allowed the gun to make full turn at a rate of 18 degrees per second, the elevation rate was 12 degrees per second. The gun could be manually operated by a crew of 7.
Similarly to the 25 mm anti-aircraft gun, machine guns intended for mounting on Japanese ships, were bought in France. The most favoured was the 13.2 mm Hotchkiss machine gun that was to replace the 12.7 mm Vickers. The purchased guns were used as basis for designing a Japanese version, which was finally approved in 1935 as 93 Shiki 13 mm Kiju. Mount specifications: maximum rate of fire – 474 rounds per minute, minimum – 425 round/min, theoretical – 450 round/min, effective – 250 round/min. The mount could be operated manually, single mount weighed 213 kg.
Another machine gun mounted on battlecruisers and battleships was the 7.7 mm gun, purchased in Great Britain and adopted in 1926. Its specifications are presented in Table 18.
The torpedo armament of the Kongō class battlecruisers – after their commissioning – comprised eight submerged 53 cm (type A) torpedo launchers, four of which were installed in the bow section and amidship, four in the stern section at the rudder shafts. The ships carried a load of twenty four 53 cm torpedoes type 44 Shiki 2 Go. During the first modernization, four launchers were removed from Kongō, Haruna and Kirishima. The amount of torpedoes taken aboard was reduced to 12. During the second modernization, all submerged launchers were removed as they were of little use for combat operations. The 6 Nen Shiki torpedo, approved in 1917, weighed 1,432 kg, its warhead was filled with 203 kg of Shimose charge. It was powered by twin-cylinder, double-acting engine similar to the Whitehead design, propelled by two four-blade, counter-rotating propellers mounted on a single shaft. Extreme length was 6,840 mm, diameter 533 mm. The torpedo’s range was 15,500 metres at 26 knots, 10,000 m at 32 knots and 7,000 m at 37 knots.
Regular complement of the Kongō class battlecruisers, in the first period of their service – according to the Confidential Navy Directive (CND) No 356 from December 1, 1914 – consisted of 52 officers, 26 ensigns, 259 non-commissioned officers, 922 (Kongō) and 942 (other units) sailors. The full complement was 1,259 (Kongō) and 1,279 (other units). First changes in crew composition took place in 1920. According to the CND No 267 from August 1, 1920, the complement comprised 38 officers, 16 officers assigned to coordinate the ships’ combat operations with other formations, 20 ensigns, 274 non-commissioned officers and 988 sailors. The complement was changed again in 1927. The Confidential Navy Directive number 91 from April 1, 1927 introduced 1,309 strong crew for Kongō and Hiei and 1,112 for Haruna and Kirishima. Another complement change took place in 1932 and concerned only Hiei, which after decommissioning, had only 826 sailors. According to the CND No 328 from December 1, 1932, the crew was constituted of 30 officers, 12 officers assigned to coordinate the ships’ combat operations with other formations, 12 ensigns, 198 non-commissioned officers and 574 sailors. The units’ complements were changed for the last time in 1937. This time, the average complement aboard the fast battleships was 1,250 sailors. The CND number 169 from April 23, 1937, determined complements for each unit setting the number of officers to 47, 16 officers assigned to coordinate the ships’ combat operations with other formations and 15 ensigns. The biggest changes affected non-commissioned officers and sailors. Detailed data concerning numbers and composition of crews of individual units is presented in Table 19.
1 T (long ton) = 1,016 ton
2 More information concerning the ships’ modernization is presented in a separate chapter.
3 The gun was renamed to 45 Kōkei 41 Nendo Shiki 36cm Hō on October 5, 1917.
4 On November 5, 1917, the gun was renamed to 40 Kōkei 8 cm Kōkaku hō and again, on March 29,1920, to 40 Kōkei 3 Nen Shiki 8 cm Kōkaku hō (Kōkaku hō – high elevation)
5 Tan – short
6 Smaller guns were designated as follows: Kōsha-Hō – anti-aircraft gun (with high elevation angle), Kiju – machine gun, Sokusha-hō – quick firing gun.
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