The 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".
Background 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 and 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.Stille, pp. 35–38 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.GlobalSecurity.org: IJN Hatsuharu class 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.Whitley, p. 224
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 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.
Design
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.Peattie & Evans, Kaigun 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.Lengerer, p. 93
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 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.Lengerer, p. 94 The Hatsuharu vessels were some shorter than the Fubuki-class vessels, but weighed per of hull length compared to the latter's per .Lengerer, pp. 94–95
Description The Hatsuharu-class ships were shorter than their predecessors, at overall. The ships had a beam of 10 metres and at full load a draft of . Despite the emphasis on weight-saving during construction, the ships were significantly overweight as completed and displaced at standard load, and at full load, nearly more than planned.Lengerer, pp. 97–98
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 rangefinder. Each of these was protected by plates of Dücol steel against strafing and shell splinters.Lengerer, p. 95
For the first time in a Japanese destroyer, a superfiring turret was fitted forward of the bridge. It was only a single gun Model A turret, to save weight high in the ship, and was mounted on a deckhouse to elevate it above the twin gun Model B Mod 2 (B-gata kai-2) turret mounted on the forecastle deck. The second twin gun turret was mounted at the rear of the ship on the main deck. These turrets were slightly heavier than the earlier Model A and Model B turrets fitted on the Fubuki-class. All turrets were fitted with the Type 3 gun.
The uptakes of the two forward boiler rooms were trunked together aft of the break in the forecastle into the fore funnel while the rear boiler room exhausted into the smaller rear funnel. Both funnels were inclined to the rear to reduce the amount of smoke that might reach the bridge. A tripod mast was fitted between the bridge and the fore funnel. Between the two funnels was the forward triple torpedo tube mount fitted on a low platform. Behind it "was a torpedo locker with its mechanical quick reload system (Kiryoku sōtenshiki jihatsu sōten sochi) for the three reserve torpedoes inside." To preserve lateral stability the aft funnel was offset to starboard while the torpedo mount was offset to port. The reload locker was also offset slightly to port and angled inboard to facilitate reloading. The middle torpedo mount was positioned behind the aft funnel on the centerline, but its reload locker was positioned identically to that of the forward mount. Superimposed to starboard and overlapping the middle mount was the rear triple torpedo mount positioned on the rear deckhouse. Immediately behind the mount was its locker positioned on the centerline, but angled slightly to the right so that its mount only had to traverse slightly to align with the locker and begin reloading. This was the first ship in history to be fitted with superimposed torpedo tubes, made necessary by the designer's insistence on fitting nine torpedo tubes despite the Navy's requirement for only six.
A small platform that carried a rangefinder was mounted above the rear torpedo locker and a searchlight was mounted on a tower behind the rear funnel. The two license-built Vickers (pom pom) anti-aircraft guns were mounted on an elevated platform at the front of the rear funnel. Curiously they were another case where the designer exceeded the requirements laid down by the Navy.Lengerer, pp. 95, 97
Propulsion The Hatsuharus carried two sets of Kampon geared steam turbines, one for each shaft. Each set consisted one low-pressure and one high-pressure turbine, plus a cruise turbine connected to the high-pressure turbine. The LP and HP turbines were connected to the propeller shaft by a two-pinion reduction gear. Each propeller had a diameter of and a pitch of . The total horsepower of the Hatsuharu class was only compared to the of their Fubuki-class predecessors, but the machinery was significantly lighter and more powerful on a unit basis. The Hatsuharus' machinery weighed only compared to the of the Fubuki class, or 396 shaft horsepower per tonne versus 347 shaft horsepower per tonne for the older ships.Lengerer, p. 101
Similarly the three Kampon Type Ro-Gō boilers used in the Hatsuharu-class ships weighed in comparison to the boilers used in the Fubuki class, but produced each while the older boilers produced . This gave a ratio of 3.6 kg per shaft horsepower for the Hatsuharus compared to the 4.1 kg per shaft horsepower of their predecessors. The newer design of boilers initially used steam pressurized to , just like the older models, but used superheating to improve efficiency while the older boilers simply used saturated steam.Lengerer, p. 102
A single 100 kW turbo-generator was fitted behind the reduction gears in a separate compartment and two 40 kW diesel generators were located between the propeller shafts. As initially completed the Hatsuharu had a range of at a speed of with of fuel. On trials, had a top speed of from at a displacement of .Lengerer, pp. 101–02
Armament The Hatsuharu-class destroyers used the same 50-caliber 12.7 cm gun as the Fubuki class, but all turrets could elevate to 75° to give the main guns a minimal ability to engage aircraft. During the war the single turret was removed on all surviving ships after 1942. The only anti-aircraft guns were two water-cooled, license-built Vickers 40-millimeter guns. These guns were deemed to be too heavy, slow-firing and short-ranged and were replaced by license-built French Hotchkiss Type 96 anti-aircraft guns in single, double and triple mounts from 1943 for the surviving ships. Exact numbers are not always known, but was carrying three triple power-driven mounts, including one mounted in lieu of the single 12.7 cm gun turret, one twin power-driven mount fitted on a platform in front of the bridge and two hand-worked single mounts in June 1944. These powered mounts were unsatisfactory because their traverse and elevation speeds were too slow to engage high-speed aircraft and more single mounts were fitted to ships in the last year of the war. For example, mounted ten single 25 guns when she was lost in July 1945. Four license-built Hotchkiss Type 93 machine guns were also fitted to Hatsushimo, but these were of limited utility against modern aircraft.Lengerer, pp. 104–05