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Hatsuharu-class destroyer
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Hatsuharu-class destroyer
The Hatsuharu-class destroyers (初春型駆逐艦, Hatsuharugata kuchikukan) were a class of Imperial Japanese Navy destroyers in the service before and during World War II. The final two vessels in the class, completed after modifications to the design, are sometimes considered a separate "Ariake class".
The provisions of 1930 London Naval Treaty stipulated that the overall destroyer tonnage for the Imperial Japanese Navy would be capped at 105,500 tons with a maximum permissible tonnage per ship of 1,850 tons. Furthermore, only 16 percent of the overall tonnage could be of this size, with the remainder not exceeding 1,500 tons per vessel. This effectively meant that additional units of the previous Fubuki and Akatsuki-class destroyers could no longer be built. The Imperial Japanese Navy responded by ordering naval architects to design ships that were lighter by at least 260 tons, and yet mount the same armament. In the end, the new class ended up with one less gun (three turrets with five 127 mm guns instead of six), with a smaller hull and displacement. This armament design was not unprecedented, however, as the two Romanian Navy destroyers Mărăști and Mărășești were fitted with two twin and one single 120 mm guns a few years prior, in 1926.
This stretched contemporary destroyer designs beyond the limits, and resulted in a top-heavy design, with severe stability problems. The weight-control measures used by designers were carried to an extreme, which further contributed to structural weakness. This was a problem shared with other Japanese ship designs of the time, which attempted to place too much armament on too small a displacement hull. This was graphically demonstrated when the torpedo boat Tomozuru capsized in 1934 during heavy seas (the "Tomozuru Incident") and when a typhoon ripped the bows off two Fubuki-class destroyers (the Fourth Fleet Incident) in 1935. As a result of these two incidents the Hatsuharu-class vessels had to be rebuilt (the first two completed had to be rebuilt twice) or modified while building to remedy their stability problems.
The Hatsuharu-class destroyers were designed to accompany the Japanese main striking force and to conduct both day and night torpedo attacks against the United States Navy as it advanced across the Pacific Ocean, according to Japan's naval strategic projections. They were to be armed much as the Fubuki class despite displacing only 1400 tons compared to the 1700 tons of the earlier destroyers. Furthermore, their fire control systems were to be more modern than the older systems and suitable for anti-aircraft use. This required the gun turrets to be modified for high-angle fire, which also meant more powerful motors to traverse and elevate the guns more quickly to engage high-speed aircraft. The torpedo launchers were to be given a protective shield to allow for use in heavy weather and to protect against splinter damage. And the Hatsuharu vessels were to be fitted with modern, enclosed command spaces protected against strafing aircraft. These requirements could only be met by adding weight high up on the ship and increased the ship's center of gravity. The only way to adhere to the allotted displacement was to try to reduce the weight of the hull and other equipment below the waterline as much as possible. But this put the ship's designers in a no-win situation as any reduction of weight below the waterline further raised the ship's center of gravity and reduced her stability.
The weight of the hull could generally be reduced by using higher grades of steel that were lighter and thinner for the same strength, reducing dimensions, particularly length, or using advanced construction techniques like welding that saved weight over the conventional riveting. The Japanese used the same high-tensile steel for the Hatsuharu class as they did for the older destroyers and chose not to increase the power of the turbines and boilers to achieve the desired high speed, but lengthened the hull to offset the reduced power of the light-weight machinery. The beam was increased to counter some of the extra top-weight, but the draft was reduced to reduce hull resistance, which also reduced stability by lessening the area of the hull beneath the waterline in comparison to the area above it, which was subject to pressure from the wind.
Extensive weight-saving measures were used during the design and construction of the hull. More frames of lighter construction were spaced more closely together to reduce the thickness of the hull plating and the extensive use of welding (only the longitudinal stringers and a few other parts were riveted) were some of the techniques utilized to reduce hull weight by 66.5 tonnes (65.4 long tons; 73.3 short tons) in comparison to the Fubuki class. Electric welding was extensively used to reduce weight although it was at an early stage of development in Japan and was still problematic. The Hatsuharu vessels were some 10 metres (32 ft 10 in) shorter than the Fubuki-class vessels, but weighed 4.9 tonnes (4.8 long tons; 5.4 short tons) per 1 metre (3.3 ft) of hull length compared to the latter's 5.09 tonnes (5.01 long tons; 5.61 short tons) per 1 metre (3.3 ft).
The Hatsuharu-class ships were shorter than their predecessors, at 109.5 m (359 ft 3 in) overall. The ships had a beam of 10 metres and at full load a draft of 3.35 m (11 ft 0 in). Despite the emphasis on weight-saving during construction, the ships were significantly overweight as completed and displaced 1,530 metric tons (1,510 long tons) at standard load, and 1,981 metric tons (1,950 long tons) at full load, nearly 130 metric tons (100 long tons) more than planned.
The hull of the Hatsuharu-class vessels retained the general configuration of the Fubuki-class destroyers with a long forecastle and a pronounced flare of the forecastle to improve sea-keeping at high speeds by adding buoyancy and reducing the spray and water coming over the deck. A large bridge structure was located at the aft end of the forecastle deck topped by four fire control stations of various types. Lowest, just above the compass bridge, was the torpedo director (Hassha shikisho), with the gunnery fire direction station (Shageki shikisho) next above. The fire director tower (Hōiban shagekito) was third from the bottom and behind it was the 3 m (9 ft 10 in) rangefinder. Each of these was protected by 10 mm (0.39 in) plates of Dücol steel against strafing and shell splinters.
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Hatsuharu-class destroyer
The Hatsuharu-class destroyers (初春型駆逐艦, Hatsuharugata kuchikukan) were a class of Imperial Japanese Navy destroyers in the service before and during World War II. The final two vessels in the class, completed after modifications to the design, are sometimes considered a separate "Ariake class".
The provisions of 1930 London Naval Treaty stipulated that the overall destroyer tonnage for the Imperial Japanese Navy would be capped at 105,500 tons with a maximum permissible tonnage per ship of 1,850 tons. Furthermore, only 16 percent of the overall tonnage could be of this size, with the remainder not exceeding 1,500 tons per vessel. This effectively meant that additional units of the previous Fubuki and Akatsuki-class destroyers could no longer be built. The Imperial Japanese Navy responded by ordering naval architects to design ships that were lighter by at least 260 tons, and yet mount the same armament. In the end, the new class ended up with one less gun (three turrets with five 127 mm guns instead of six), with a smaller hull and displacement. This armament design was not unprecedented, however, as the two Romanian Navy destroyers Mărăști and Mărășești were fitted with two twin and one single 120 mm guns a few years prior, in 1926.
This stretched contemporary destroyer designs beyond the limits, and resulted in a top-heavy design, with severe stability problems. The weight-control measures used by designers were carried to an extreme, which further contributed to structural weakness. This was a problem shared with other Japanese ship designs of the time, which attempted to place too much armament on too small a displacement hull. This was graphically demonstrated when the torpedo boat Tomozuru capsized in 1934 during heavy seas (the "Tomozuru Incident") and when a typhoon ripped the bows off two Fubuki-class destroyers (the Fourth Fleet Incident) in 1935. As a result of these two incidents the Hatsuharu-class vessels had to be rebuilt (the first two completed had to be rebuilt twice) or modified while building to remedy their stability problems.
The Hatsuharu-class destroyers were designed to accompany the Japanese main striking force and to conduct both day and night torpedo attacks against the United States Navy as it advanced across the Pacific Ocean, according to Japan's naval strategic projections. They were to be armed much as the Fubuki class despite displacing only 1400 tons compared to the 1700 tons of the earlier destroyers. Furthermore, their fire control systems were to be more modern than the older systems and suitable for anti-aircraft use. This required the gun turrets to be modified for high-angle fire, which also meant more powerful motors to traverse and elevate the guns more quickly to engage high-speed aircraft. The torpedo launchers were to be given a protective shield to allow for use in heavy weather and to protect against splinter damage. And the Hatsuharu vessels were to be fitted with modern, enclosed command spaces protected against strafing aircraft. These requirements could only be met by adding weight high up on the ship and increased the ship's center of gravity. The only way to adhere to the allotted displacement was to try to reduce the weight of the hull and other equipment below the waterline as much as possible. But this put the ship's designers in a no-win situation as any reduction of weight below the waterline further raised the ship's center of gravity and reduced her stability.
The weight of the hull could generally be reduced by using higher grades of steel that were lighter and thinner for the same strength, reducing dimensions, particularly length, or using advanced construction techniques like welding that saved weight over the conventional riveting. The Japanese used the same high-tensile steel for the Hatsuharu class as they did for the older destroyers and chose not to increase the power of the turbines and boilers to achieve the desired high speed, but lengthened the hull to offset the reduced power of the light-weight machinery. The beam was increased to counter some of the extra top-weight, but the draft was reduced to reduce hull resistance, which also reduced stability by lessening the area of the hull beneath the waterline in comparison to the area above it, which was subject to pressure from the wind.
Extensive weight-saving measures were used during the design and construction of the hull. More frames of lighter construction were spaced more closely together to reduce the thickness of the hull plating and the extensive use of welding (only the longitudinal stringers and a few other parts were riveted) were some of the techniques utilized to reduce hull weight by 66.5 tonnes (65.4 long tons; 73.3 short tons) in comparison to the Fubuki class. Electric welding was extensively used to reduce weight although it was at an early stage of development in Japan and was still problematic. The Hatsuharu vessels were some 10 metres (32 ft 10 in) shorter than the Fubuki-class vessels, but weighed 4.9 tonnes (4.8 long tons; 5.4 short tons) per 1 metre (3.3 ft) of hull length compared to the latter's 5.09 tonnes (5.01 long tons; 5.61 short tons) per 1 metre (3.3 ft).
The Hatsuharu-class ships were shorter than their predecessors, at 109.5 m (359 ft 3 in) overall. The ships had a beam of 10 metres and at full load a draft of 3.35 m (11 ft 0 in). Despite the emphasis on weight-saving during construction, the ships were significantly overweight as completed and displaced 1,530 metric tons (1,510 long tons) at standard load, and 1,981 metric tons (1,950 long tons) at full load, nearly 130 metric tons (100 long tons) more than planned.
The hull of the Hatsuharu-class vessels retained the general configuration of the Fubuki-class destroyers with a long forecastle and a pronounced flare of the forecastle to improve sea-keeping at high speeds by adding buoyancy and reducing the spray and water coming over the deck. A large bridge structure was located at the aft end of the forecastle deck topped by four fire control stations of various types. Lowest, just above the compass bridge, was the torpedo director (Hassha shikisho), with the gunnery fire direction station (Shageki shikisho) next above. The fire director tower (Hōiban shagekito) was third from the bottom and behind it was the 3 m (9 ft 10 in) rangefinder. Each of these was protected by 10 mm (0.39 in) plates of Dücol steel against strafing and shell splinters.
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