Hakugei Class Submarine Tender (Part 1, 1928-1940):
In order to provide support to the large number of submarines that were planned to enter service by the late 20's, Koko no Kaigun immediately started the developement of a dedicate Submarine Tender. The closest example of such ship to be examined was the Japanese Jingei class that was about to enter service by mid 1923, yet those ships would have been unable to support the larger Kaidai-type submarines currently under developement by the IJN. Since Koko's Naval Staff had eventually planned to put in service larger, similar, units after all the smaller Ki-3 Class units had been completed it appeared obvious that the support ships had to be of a larger design.
By the time the first ship, to be named Hakugei, was laid down at Yamatogawa Shipyards in late 1923, the planned tender had grown by almost 50% if compared with the original specifications. Hakugei was launched in 1926 and commissioned by late 1928, just months before the first submarines of the Ki-3 class entered service. a second unit, Shiroiruka, started construction at Yamatogawa in 1926, just after Hakugei's launch.
The tenders were 193,7m long overall, had a beam of 18,2 and drafted 6,6m. displacement was 11.993tons at standard load, rising to 14.478 at full load. Mixed coal and oil-firing boilers powered two geared turbines with 20.348shp, driving two screws for a maximum speed of 21 knots. Endurance was 10.400 nautical miles at 14 knots. The hull was not armoured, but the ships were nevertheless armed with two twin 140mm/50 turrets fitted forward in a superfiring arrangement. Turrets beign the sole armoured parts of the ship, protected by 50mm steel plates on faces, 10mm on roofs and 30mm on hoists. Two 120mm/45 single anti-aircraft guns and two 7.7mm machine guns were also carried. The stern of the ship was dedicated to floatplane operations: a Type1 catapult was fitted on the quarterdeck, while an enclosed hangar in the after part of the superstructure housed two Nakajima E2N reconnaissance floatplanes.
Overall, the ships had a total bunkerage of 5.339tons of oil to replenish Submarines tanks, other than beign able to carry a full stock of 76 torpedoes and up to nine periscope sets.
![[ img ]](http://i.imgur.com/JC6I7GO.png)
Shiroiruka had been launched in 1929, and had started her fitting out when the London Naval Treaty was signed. The treaty heavily limited Koko no Kaigun allowed tonnage of Submarines, stalling the construction plan for years, effectively cutting the fleet to just 10 subs. The ship was thus givn a lower priority and was commissioned only in late 1932. She was given newer 40mm machine guns in place of the older 7.7mm ones, her bridge was fully enclosed and the aft catapult was modified into a Type2 in place of the Type1 fitted on Hakugei.
![[ img ]](http://i.imgur.com/PKEizcm.png)
A third unit, Kokukujira, had been laid down at Yamatogawa after the launch of Shirouruka, but Treaty limiatons to the sumbarine fleet made her completion unnecessary. Since her hull was at a very early stage of construction further work were canceled in november 1930. Kokukujira was scrapped on the slipway and the materials intended for her construction were used for Shiroiruka fitting out or diverted to other ships under construction.
During the late 30's both ships recieved a twin 25mm machine gun above the hangar and had the 7,7 and 40mm machine guns replaced by two twin 13mm ones. Hakugei had her catapult reeplaced by a Type2 model and her bridge was enclosed. Both had the floatplane complement upgraded, with Kawanishi E7K replacing the old Nakajima E2N.
![[ img ]](http://i.imgur.com/pmOYsPJ.png)
Hakugei operated as the flagship of the newly formed Sensui Sentai 2 in 1929, Shiroiruka replaced Nayoro in Sensui Sentai 1 once she was commissioned in 1932. Both ships mantained their roles for the rest of the decade.
Ships in class: (laid down-launched-commissioned - fate)
hakugei 1923-1926-1928 - ?
shiroiruka 1926-1929-1932 - ?
kokukujira 1929-/-/ - Canceled and scrapped 1930