Shizuha Class Destroyer (part 1, 1933-1940):
As the London Naval Treaty entered into effect the only possible way for Koko no Kaigun to keep building destroyers was to retire older units. The Kuchikukan-14 Class and the Sato were the ships upon which the choiche befell. Even so, given the number of Yuuka and Reisen class planned or that were still to enter service, only four extra units could have been built. More so, they must have displaced no more than 1.500T because the Reisens ate all the extra tonnage allowances permitted by the treaty.
In november 1930 the Naval Staff issued the requirement for a new class of destroyers to be built. With a requirement of a maximum tonnage of 1.500 at standard load KnK designers joined IJN ones to develop a joint design. The resulting ship would have been 109,5m long, 10 abeam and drafting 3,3 for a planned displacement of 1.400T, the armament called for five 5-inch guns (127mm) and nine 610mm torpedo tubes in triple launchers to be installed, top speed was planned at 36knots for a range of 4.000nm at 14knots. The ships were ordered in Japan as the Hatsuharu Class and as the Shizuha Class in Koko.
The lead ship, Shizuha, was laid down at Kumoi Arsenal on December 18th 1931 and launched on December 17th 1932. While she was still fitting out, IJN Hatsuharu trials revealed the ship to be prone to roll heavily, demonstrating that her metacentric height was too low. As a contermeasure the upper levels of Shizuha's bridge were slightly reduced and bulges were added, bringing the overall beam to 10,6m and the rudder was modified. Interestingly, the Shizuha turned out to be some 40 tons lighter than an Hatsuharu, displacing 1.490T instead of 1.530. Still both ships were overweight compared to their planned weigth.
The second ship of the class, Minoriko, was laid down December 31st 1932 at Kumoi arsenal shortly after the launch of Shizuha. The last two units, Hina and Nitori, started construction at Kousaten Navy Yard in late 1933. In March 1934 Minoriko was roughly two months away from launch when the IJN torpedo boat Tomozoru disastrosly capsized during night torpedo trials off Sasebo. The incident prompted an immediate revision of all ships currently under construction or recently completed for both the IJN and KnK, with the Hatsuharu/Shizuha beign among the most deficent ones when it came to stability and topweight issues. Construction on the three ships was halted and Shizuha was taken out of service while designers returned to the drawing board to find a solution for the problems. Japanese Hatusharus had their bridgework and armament reduced to counter topweight, and ballast led to a lowered top speed from 36 to 33 knots, Kokoan Shizuhas went through a much more extensive and complex rebuilds.
Between their constructionw as approved and the Tomozoru incident, Koko had experienced a government change and a coup d'etat that ultimately strenghtened Kusako Morimoto's leadership. As soon as his new cabinet took office a naval rearmament plan had been immediately approved. A plan that would have progressively disregarded treaties as it would be later proved by the joint Kokoan/Japanese denunciation of the Washinton Naval trety in december 1934.
Under the new provisions designers scrapped the 1.500T weight limitations and drafted a new ship from the old plans. By fall 1934 works restarted on Minoriko, Hina and Nitori. In an overly complex fashion the hull was cut apart at midship and anewly built 2,3m section was added inbetween bringing the total lenght of the ships to 111,8m and the beam to 10,1. The engines were replaced with new boilers generating 56.000shp installed in place of the planned 40.000shp ones. Supestructure volume was vastly reduced, the funnels cut down and the entire aft deckhouse replaced by a much smaller structure. The forward, superfiring, single 127mm gun was moved to the quarterdeck and all three triplee torpedo launchers were landed, replaced by two quadruple sets. A new, larger, rudder was also installed. The large-scale rebuild strained to the brim the capabilities of the shipyards involved, but in effectively turned the three destroyers into new ships. Their displacement had risen from 1.490 to 1.796T, also increasing draft to 3,5m, but thanks to the increased engine power the top speed fell by just 0,3knots from 36 to 35,7. Minoriko, Hina and Nitori were eventually commissioned between August and November 1935. Shizuka was docked at Toumachi Naval arsenal to underwent a similar, massive reconstruction, eventually rejoining the fleet modified like her sisters only by early March 1936.
The first rearmament bill not only stretched the lives of the last Kuchikukan-27 units and saved Sato from the scrapyards, but also called for a restart in Destroyer production. On October 24th 1934 five more ships of the Shizuha class were ordered, this time to be built from the start to the modified design. The first ship, Momiji, was laid down at Kousaten Navy Yard by the end of the year, two more, Mion and Kanako, followed in 1935 and another two, Suwako and Iku, in 1936. Their orders split between Toumachi and Hoshiguma Naval Yards. When in September 1935 many IJN vessels were damaged in what will be later known as the Fourth Fleet Incident the design of the five newer ship was revised once again, relocating armament and deckhouses placement and reducing the bridge for more topweigh-saving measures, although it ultimately lenghtened building time. The so-called second batch of the Shizuha class, also known as Type II or Momiji subclass had it's ships enterinjg service between 1937 and 1939. The ships displaced 1.788T, slightly less than the four earlier sisters. They sported newer gun turrets and more advanced fire-control equipment, other than an increased depth charge complement, dedicated RDF room and twin 13mm machine gun as light anti-air guns in place of the 40mm ones fitted on the other ships of the class.
Overall, while the massive rebuild the ships solved the topweight and stability issues allowing tho retain almost of the armament and speed of the original design the works were so extrensive that they stretched the shipyards capabilities to the point that just nine ships were built over the course of eight years despite beign ordered on four different shipyards. This, coupled with other slipways beign committed to the building of other ships under the rearmament plans, prevented the restart of full-sized destroyer production until 1937 despite it was intended to ignore treaty limitations since December 1934.
The Sizuha class ships formed up Kuchikutai 18, 19 and 20. the first made up Suirai Sentai 6 together with kuchikutai 2, the other two operater together under Suirai Sentai 4.
Ships in class: (laid down-launched-commissioned - fate)
Shizuha 1931-1932-1933 - ?
Minoriko 1932-1934-1935 - ?
Hina 1933-1934-1935 - ?
Nitori 1933-1934-1935 - ?
Momiji 1934-1936-1937 - ?
Mion 1935-1936-1937 - ?
Kanako 1935-1936-1937 - ?
Suwako 1936-1937-1938 - ?
Iku 1936-1938-1939 - ?