The main difference in design between the
Akatsuki vessels and the standard
Fubuki-class was the use of a new high-pressure boiler, which enabled the number of boilers to be reduced from four to three without a reduction in power. This also enabled the fore smokestack to be made narrower than on standard
Fubuki-class vessels, and this feature was the most evident visual recognition feature between the two designs. Other improvements over the
Fubuki class included a larger bridge structure, with the addition of another level to house improved fire control facilities, and a splinter-proof torpedo launcher/turret, which allowed the torpedo launcher tubes to be reloaded in action. The four ships incorporated many weight-saving measures, and was the first all-welded Japanese ship. However, the
Akatsuki class shared a number of inherent design problems with the
Fubuki class. The large amount of armament combined with a smaller hull displacement than in the original design created issues with stability. After the
Tomozuru Incident, in which the basic design of many Japanese warships was called into question, additional
ballast had to be added. In the
Fourth Fleet Incident, during which a
typhoon damaged virtually every ship in the
Fourth Fleet, issues with the longitudinal strength of the
Akatsuki-class hull was discovered. As a result, all vessels were reconstructed from 1935 to 1937. An additional 40 tons of ballast was added, the bridge reduced in size and the height of the smoke stacks was decreased. The number of torpedo reloads were reduced from nine to three (for the center launcher only), and fewer shells were stored for the guns. The amount of fuel carried was also increased to help lower the center-of-gravity. This increased the displacement to 2050 tons standard load and over 2400 tons full load. The rebuild reduced the top speed slightly to 34 knots.
Armament The
main battery consisted of six
Type 3 127 mm 50 caliber naval guns, mounted in pairs in three weather-proof, splinter-proof, gas-tight
gun turrets. These guns were
dual purpose guns that could be elevated to 75 degrees, making them the world's first destroyers with this ability. Ammunition was brought up on hoists from
magazines located directly underneath each gun turret, which had a far greater rate of fire than those of other contemporary destroyers in which ammunition was typically manually loaded. However, the gun houses were not bulletproof, and were thus actually still gun mounts, rather than proper turrets. The three triple
torpedo launchers used on the standard
Fubuki class were retained, and originally Type 8 torpedoes were carried. These were later replaced with the
Type 93 "Long Lance" oxygen-propelled torpedoes during
World War II. Anti-aircraft capability was initially two
Type 93 13 mm AA guns mounted in front of the second stack. In 1943, an additional pair of Type 93 guns was mounted in front of the bridge, which was later changed to
Type 96 25 mm AA guns on and in January 1944. These vessels also lost one of their aft guns in April 1944 in exchange for two triple Type 96 guns, and another pair of triple Type 96 guns was added between the aft torpedo mounts.
Hibiki had another 20 single-mount Type 96s added, as well as a Type 22 and Type 13 radar, before the end of the war. ==Operational history==