Chidori class Torpedo Boats (1933)

Japan, 1933-45.

The Chidori-class torpedo boat (千鳥型水雷艇, Chidori-gata suiraitei) were Imperial Japanese Navy torpedo boats, the first since decades, built in the interwar and seeing heavy action in the Second World War. The design was an attempt to circumvent, very much like Italy, tonnage limitations on warships. The IJN staff ina predictable pattern wanted as much armament mounted for such as small displacement. The capsizing of Tomozuru shortly after completion in heavy weather became a scandal putting under the projector a decade-long very risky approach on IJN warship basic designs. The class required extensive modifications like the rest of the fleet. They saw service in the Battle of the Philippines and Dutch East Indies campaign as escorts and three were sunk, the last seized in Hong Kong.

IJN Chidori colored by hirootoko JR.

Development

Under the terms of the 1930 London Naval Treaty Japanese Politicians signed, the Imperial Japanese Navy was forced into the same tonnage caps for all ships type as the other signatories, UK, US, France and Italy. The tonnage cap for destroyers was severe in a ship type cap, thus, compared to the global destroyer tonnage authorized, it limited how many can be built. Engineers on the early “toothbrush” 1920 destroyer types followed a pattern to maximize armament already, but by 1926 the IJN wanted the new “special type” to be generalized in the fleet. And these were much larger vessels. Tricks led to publishing both under-evaluations of tonnage while engineers were asked to deploy treasures of ingenuity to cram as much armament they could on the hulls as defined.

However, Japanese naval planners, just like Italian and German ones (from 1935 onwards) realized that a treaty loophole left the below 600-ton class unadressed. Meanning they were considered not worthy as warships and thus assimilated to auxiliaries (just as aircraft carriers below 10,000 tonnes), and hence, tonnage free. But despite the small tonnage, half that of a “special type” (Fubuki) planned to arm them ALSO with half the armament of a Fubuki class. The logical designation was thus “torpedo boats” to further match international expectations and exclude them from further scrutiny. Four were ordered as part of the 1931 Maru 1 Programme to test the waters with this new type, the first of a planned class of twenty that could provide useful escort service, like 1920s destroyers when the second world war started, freeing the “special types” to capital fleet duties.

Thus Japan joined the “axis club” trying to cheat on the treaty by building still valuable warships on “free tonnage”. But in the end, it’s torpedo boat production was limited. The first class proved over-ambitious and this was paid dearly, with a loss and full, costly reconstruction and compromises, the next Otori class were an enlarged design already above treaty limitations but better adapted to their armament. Eight were built, on a good design that did nt required modifications (launched 1935) but the IJN recoignized these vessels had a limited usefulness and ultimately cancelled the next eight (and thus, the whole twenty in the program). Instead, it was decided to concentrate on ASW protection of convoys, and thus on a new generation of sub-chasers. This was unlike German and Italy whith both embraced the concept of torpedo boats and built new classes until the end.

Design & Construction of the class

When the Chidori class was planned in 1931, Japan stopped building torpedo boats since 1900 with the 2nd class “N°67 class”. After the larger Shirataka class (1899), the IJN jumped on the destroyer bandwagon with the 300t Ikazuchi class (also launched 1899). So three decades went by and Japan had to start again on this type from scratch. It was not alone doing this. The unexpected return of torpedo boats, a type that had its fad roughly between 1878 and the late 1890s, was succeeded by more versatile and seaworthy destroyers (or “counter-torpedo boats” ships). The predator became the third essential type in service in WW1. The torpedo boat concept did not died out and morphed into the much smaller motor torpedo boat. But the Washington and later London treaties which limitations angered naval staff left to a systematic exploitation of its loopholes, and to a resurrection of the “torpedo boat” that was unplanned and overlooked.

Construction

The IJN Chidori, and her sister Tomozuru were laid down practically at one year interval at Maizuru Naval Yard. Chidori was also launched a few months earlier, hence the class name in most publications. Conway’s however call it the Tomozuru class and it’s unclear why. Chidori really was the first in class. She was started in October 1931, launched in April 1933 and completed in November of the same year, and IJN Manazuru from Fujinagata Shipyard was the second in class chronologically. Tomozuru (from Maizuru Naval Arsenal) was the thord laid down on 11 November 1932, launched on 1 October 1933 and completed on 24 February 1934 and Hatsukari was the second built at Fujinagata Shipyards, laid down the last on 6 April 1933, launched on the next 19 December and completed also last on 15 July 1934. Their early career quickly underlined massive design issues. Like so many classes before they tried to do much with their limited treaty-bound tonnage. The idea was to stay below 600 tonnes standard.

Names

There were no debate about to name them or give them numbers, as this was already decided earlier with 1920s second class destroyers as part of the “Eight-eight fleet plan”, the destroyerrs of the Kamikaze class were completed with numbers and by August 1928 with the great deal of confusion in manoeuvers and exercises and poor esprit de corps in the crews, it was decided to revert to names. In the case of these new torpedo boats in 1931, instead of the usual weather events (winds, waves, etc.) since this was a new type, it was decided to go for animal names, in that case, birds, smaller and more lively than destroyers perhaps. The crane was a revered animal in Japan since medieval times and symbol of passing seasons due to their migrations. This was the theme here. Hence, Chidori was 千鳥 ‘plover’, Manazuru 真鶴 was a ‘white-naped crane’, Tomozuru became 友鶴 ‘flight of cranes’, and Hatsukari 初雁 was the very poetic ‘first wild goose of the season’. No anticipation on the 1944 “turkey shoot”, the season was not on already… The next Otori class continued this naming tradition of (partly migratory) birds with storks, magpies, peregrine falcons, herons and doves.

Hull and general design

Initial design as completed in 1933. Note the bulges added at the end of the trials to stabilize them.

As initially completed, on plans, the Chidori-class torpedo boats were comparable with early next-gen Italian torpedo boats, and otpimistically were declared at 535 long tons (544 t) on standard load when constrruction started in late 1931. In reality when completed on trials, they displaced 116 tonnes more at 651 tonnes, “light” displacement on trials, thus, minimal amount of fuel oil for a short run and no ammunition, food and even reduced crew. This was still above treaty limits but when Chidori started her trials in December 1933, the international situation was tense enough that it did not cause any wave, plus the official displacement in publications remained the same. When fully loaded with full provision of oil fuel, ammunition, food and full crew, this went upt to 738 long tons (750 t) at full load.

Dimensions were below even the 1922 second-class destroyer (The 860t Wakatake class was 85.3 x 7.9 x 2.5m or 280 x 26 x 8.2 ft). At 82 meters long overall (269 ft) for a beam of 7.40 m (24 ft 3 in), they had an average draft of 2.50 m (8 ft 2 in). The hull ratio was thus 11:1, superior to even these destroyers. They were quite narrow to preserve speed, but with all their armament installed, dedidedly top-heavy. Engineers made a ship in conformity with the naval staff desires, but technically they were flawed and they probably knew it.

The layout of that class was very different than for a 2nd class destroyer as well, if hull lines were about the same, the bow design was arched like a modern Fubuki class, as the rounded poop, recesses at the end of the long, full forecastle and hull proportion in general resembled as a much scaled-down Fubuki. The forecastle was lower over the water and thus potentially more “wet”, this became quite clear in early service. Seen from profile, the main forward gun was placed at mid-distance between the bow tip and bridge to give it maximum traverse angles when firing aft, but this was a weight penalty.

The bridge had a rounded base and it was two level high like any “special type” with the upper bridge being open with a light removable structure on top, rounded and generously glassed. There was the usual rear upper fire control deck with telemeter. Next came the tripod foremast, supporting a spotting top. Next, was a single raked, capped, funnel with exhaust lines truncated into her, and the usual mushroom cover protecting its base. Behind it was a AA gun platform, followed by the two torpedo tubes banks on deck, full size at 533 or 21-in, plus reloaded underneath the funnel. A light walkway was installed on top of the tubes banks. Next came the quartedeck house and aft tripod mast. For the turreted armament, some level-headed judgment had the three guns installed in a aft twin turret and single mount bow turret. Still, they were turrets offering some protection against the elements and comparable to Special Type turrets, not 1920s destroyers simple masks. The poop featured two massive paravanes and their laying gear for anti-mine duties, and it seems they had a rack aft with nine depth charges for ASW work. The crew was about 113 men total, with four rescue boats close to the funnels, two whalers and two pinnaces.

Powerplant

The IJN wanted these new vessels to be fleet-compatible, meaning having the same speed as its cruiser, fleet carriers and first line destroyers. For this, two Kampon geared turbines were installed, driving two shafts. They were fed by two Kampon water-tube boilers, producing a total of 11,000 shaft horsepower (8,200 kW). Engineers managed nin such small space to rate them for a top speed of 30 knots (34.5 mph; 55.6 km/h), not the 36 knots of special types, but the baseline speed for fleet operations. In addition they hstill had a generous range of 3,000 nmi (5,600 km) at 14 knots (16 mph; 26 km/h), or 9,000 nmi (17,000 km) at 10 knots (12 mph; 19 km/h), equal to destroyers, from a bunkerage of 152 tonnes (150 long tons; 168 short tons) of fuel in her tanks. The latter were placed low in the hull and along it in separate compartments to distribute the load. However nothing was planned as a filler or compensation when they were emptied in prolongated exercises, further exacerbating the top-heaviness of the design.

Armament

The Chidori-class were exceedingly heavily armed as seen above, and in the initial configuration their three full size main battery guns were the same three 127 mm (5.0 in) Type 3 guns found on the Fubuki and their true contemporary the Hatsuharu class, mounted in a forward single-gun power-driven gun turret at the forecastle, forward of the bridge. The other two were in a twin mount comparable to the one installed on the Fubuki, power-driven on the deck aft. The anti-aircraft armament was not a certainty as sources conflicts. Conways went for a single license-built Vickers 40 mm (2 pounder pom pom) which is commonly shared by authors, while others pointed instead instead to a single, much lighter 12.7 mm (0.50 in) Type 93 heavy machine gun.

In any case, the torpedo armament as seen above comprised two sets of twin 533 mm (21 in) torpedo launchers instead of the “standard special type” new 24 inches or 610 mm long lance. Some sanity prevailed to installed these heavy mounts and instead revert to the older, but still very capable 21-inches or 533 mm models aplenty ion the inventory for the previous “toothbrush” type destroyers until the Mutzuki. Probably the onl concession the engineers obtained. These pairs were mounted abaft the single funnel facing opposite direction. They were of a light shield type, not the better enclosing type seen later, another concession to save weight. The large paravanes aft were on heavy mounts anchored on sponsoned positions at the extreme of the poop, and the depth charges were placed between them and the aft turret, composed of two Type 94 projectors (Y-guns) facing either broadside, with a transverse reload rack close by. In total the total armament represented 22.7% of the displacement, all on deck (thus as topweight).

12.7 cm/45 3rd Year Type naval gun

It is likely the Chidori carried the Model B turret after and its single-gun variant forward. The twin mount Model B aft weighted alone 18.5 tonnes (18.2 long tons; 20.4 short tons). Round: 23 kg (51 lb) HE, illumination, incendiary shrapnel (sankaidan) for AA use, flat-nosed ASW (1943). 1945: HE developed with added charge for 23,025 metres (25,180 yd).
Propellant: 7.7 kg (17 lb) 30 DC.
Muzzle velocity:
-Common Type 0 HE 23 kg (51 lb)/1.88 kg (4.1 lb): 910–915 m/s (2,986–3,002 ft/s)
-Common Type 1 HE 23 kg (51 lb)/1.88 kg (4.1 lb): 910–915 m/s (2,986–3,002 ft/s)
-Illumination 23 kg (51 lb): 750 m/s (2,500 ft/s)
-ASW 20.9 kg (46 lb)/4 kg (8.8 lb): 250 m/s (820 ft/s)
-HE 1945 LG type 27.9 kg (62 lb)/2.2 kg (4.9 lb): 910–915 m/s (2,986–3,002 ft/s)

40 mm/62 “BI” Type 91

Vickers licenced 2-pdr HA (40 mm). Installed on the platform aft of the funnels in most sources. Wether it was kept after trials is subject to debate. Here are its specs:
Gun Weight 619.5 lbs. (281 kg) including cooling water, oa lenght 98.5 in (2.502 m), barrel 62 in (1.575 m).
Round 2.95 lbs. (1.34 kg) HE 11.995 in (30.47 cm). Muzzle Velocity 1,969 fps (600 mps).
Rate Of Fire 200 rpm cyclical, 60-100 rpm practical. Max ceiling 85° 13,110 feet (4,000 m).

13.2 mm Type 93 heavy machine gun*

Barrel Lenght 140 cm (55 in) total, 988 millimeters (38.9 in) barrel alone for a mass of 42 kgs (93 lb) empty.
Shell: 13.2×99mm Hotchkiss 13.2 mm. Gas-operated fully automatic +85° elevation, 450 rpm max, effective range 1,000 meters (3,300 ft).
Feed system: Classic box magazine holding 30 rounds, spiderweb anti-aircraft iron sight. *Possibly after early refit.

Type 6 Torpedo

1917 mass produced torpedo initially planned for battlecruisers and battleships of the “8-8-8” plan, later cancelled with the Washington treaty. Standard 53 cm torpedo for new cruisers and destroyers when metric was used also for these models.
⚙ specifications Type 6
Weight 3,157 lbs. (1,432 kg), Dimensions269 in (6.84 m).
Propulsion: Kerosene-air wet-heater for 7,000 m/35, 10,000m/32, 15,000m/26 knots.
Warhead 448 lbs. (203 kg) Shimose, straight course model.
Likely two spare torpedoes were carried either side of the amidship structure. The twin mount light shield somewhat protected the operator and its dahsboard.

Depth Charges

Standard Type 95, 30.5″ by 17.7″ (77.5cm by 45cm). 220 lb (100 kg) charge, Type 88 explosive (ammonium perchlorate and ferrosilicate). Fuse using a water inlet. 100 feet (30m) and 200 feet (60m) settings (after the revelations of a US Congressman).

⚙ Original 1933 specifications
Displacement	535 long tons (544 t) standard, 738 long tons (750 t) full load
Dimensions	82/79 x 7.4 x 2.5 m (269 ft x 24 ft 3 in x 8 ft 2 in)
Propulsion	2 shafts Kampon impulse turbines, 2x WT boilers 11,000 shp (8,200 kW)
Speed	30 knots (34.5 mph; 55.6 km/h)
Range	3,000 nmi (5,600 km) at 14 kn (16 mph; 26 km/h)
Armament	3× 127 mm Type 3, 12.7 mm HMG, 2×2 533 mm TTs (8), 9 DCs
Crew	120

Tomozuru affair and Modifications

Stability explanations After the lead vessel Chidori was completed, it was discovered during trials that her center of gravity was too high and that she was 92 tonnes (91 long tons; 101 short tons) overweight. To compensate she had 250 mm (9.8 in) bulges creating pockets that can be filled with steel, that were later fitted to the rest of the class. But on the long run this proved insufficient. Indeed on 12 March 1934 just before completion, Tomozuru was sailing with Chidori, led by the cruiser Tatsuta, in night torpedo training. The weather was already foul during the day but degraded fast this night, so far the commander communicated by radio to all ships calling it off, but only a at 03:25.

All were to return to port but the following morning, Tomozuru was never accounted for. A search was launched after dawn, in choppy seas and poor visibility but improving. It went all moening and in the afternoon as the weather improved. Ultimately her wreck was spotted at 14:05. Piraculously she had not sunk but capsized, turned over and presenting her keel. Air pockets inside kept her afloat for many hours. Ships arrived and tried to catch survivors, but only rescued fourteen. Of her 113-man crew, the bulk went down, drown, trapped inside the inverted hull and filling compartments. She was towed as she was to Sasebo, returned after a frantic effort, then docked, and then rebuilt in drydock until returning to service as the reconstruction blueprint for her sisters.

This disaster was a national tragedy. It forced the Imperial Japanese Navy to look again its past designs, now all at risk, and review the stability of every ship recently completed as well as under construction or in design phase. Some heads fell, and ultimately the Chidori class had to be massively modified to stay in service. A preliminary enquiry showed Tomozuru was already low on fuel when the order was given to sail back, and had her full complement of 113 men, full armament with all magazines filed to the brim for realistic conditions. She probably had to fend off coming waves, but at some point was overturned sudenly by one, perhaps a rogie wave or simply a big one coming from an awkward angle. She capsized, rapidlly filled underwater, and the surviving crew was forced to evacuate into the bottom of the hull still having trapped air in some compartments, just enougn to stay afloat.

Reconstruction Details

The reconstruction concerned many aspects, but mostly it was about reducing her excessive armament. The bridge structure was cut down by one level as well, and the bulges were removed, whereas the bottom hull was rebuilt with more filling compartments, a displacement that increased to 815 long tons (828 t) with the addition of 60–90 tonnes (59–89 long tons; 66–99 short tons internal ballast plus the fitting of a lead battast keel.

Her top speed post-modifications dropped to 28 knots (32 mph; 52 km/h), range down to 1,600 nmi (3,000 km) at 14 knots (16 mph; 26 km/h). The result was that she could not longer be part of fleet operations and like her sisters and older 2nd class DDs she was now relegated to escort work only. This was a far less appealng proposition and the whole program was cancelled, and of the sixteen remainong ships, only the first half, alrady planned to be laid down, was completed (as the Ōtori class) after deep modifications. They ended as much larger and their own class.

The Tomozuru Incident of March 12, 1934 saw notably the original 127 mm (5-in) Type 3 guns replaced by smaller single 12 cm/45 3rd Year Type naval guns. One twin torpedo launcher was removed as well as all the spare torpedoes, and if present, the 40 mm AA or Type 91 HMG swapped for a 7.7 mm LMG which became standard, sparing even more weight, but now a token AA defence. In fact a total of 100 tons of ballast between the reworked internal compartments and new ballast keel helped lowering the center-of-gravity, to the cost of speed. The turrets were replaced by light masks, smaller, lighter ones, and the three mounts were now separated, one aft amidship, one aft and one forward. The poop paravanes were removed as well.

In 1944, the rear gun was removed, replaced by a twin Type 96 25mm AA gun for better AA defence. Another one was placed in front of the bridge plus six single-mounts in various locations. Depth charges increased up tp 48. IJN Hatsukari by December 1944 had thus two 12 cm/45 3rd Year Type naval guns and ten Type 96 25mm AA guns two 533 mm (21 in) torpedo tubes and 48 depth charges. The weight of the AA returned some top weight, but the previous changes were so deep, there was some room left for manoeuver.

Scheme, Chidori post-reconstruction

Russian rendition after reconstruction (pinterest)

⚙ General characteristics after rebuilding
Displacement	600 long tons (610 t) standard, 815 long tons (828 t) FL
Dimensions	Beam 8.10 m (26 ft 7 in) with bulges. Draft 2.38 m (7 ft 10 in)
Propulsion	2 shafts Kampon impulse turbines, 2x WT boilers 11,000 shp (8,200 kW)
Speed	28.0 knots (32.2 mph; 51.9 km/h)
Range	1,600 nmi (3,000 km) at 14 kn (16 mph; 26 km/h)
Armament	same but 1×2 533 mm TTs, no reloads
Crew	120

Evaluation

ONI rendition of the Chidori class in 1942 (after reconstruction).

Overall, the costly rebuilding (in addition to the drama and losses of life) of the class was a firm braking of the IJN, forced by the events, into more realistic considerations, rebalancing what its desired and the hard reality of gravity. Having that much bang on this package was pure delusion. The engineering culture at the time and its submission to the political and military power stood no chance of having their warnings heard. They just obeyed orders. This was less free-flowing and open to reports as in other Navies of the time, at least to an extent. The failure of the over-optimistic Chidori class, and unimpressive Otori after a long redesign, made the class far less useful to the IJN, explaining Japan was the only member of the axis not merely interested in that type in the interwar. Instead, efforts led to the design of dedicated escort destroyers on the higher end, and on dedicated escorts and sub-chasers in the other end.

In 1937, the four torpedo boats joined the Torpedo Flotilla 21. They sortied to help in the Battle of Shanghai. When WWI saw action in the Battle of the Philippines and the Dutch East Indies campaign. Chidori and Manazuru were bacl to Japanese home waters and their unit was disbanded by the spring of 1942. They ended in escort until the remainder of the war. Hatsukari and Tomozuru however remained in their designated area until the rest of the war, escorting convoys. Tomozuru was back home late in the war and Hatsukari entered Hong Kong on 21 May 1945. She defended the skies until the end of war, and after the local surrender, was seized by the Royal Navy, later scrapped.

IJN Chidori (1933)

IJN Chidori was laid down at Maizuru Naval Arsenal on 13 October 1931, launched on 1 April 1933 and completed on 20 November 1933. She was modified from November 1934. Construction at Maizuru Workshop in 1931 was not secret but its excessive armament was. But whatever engineers promises, trial displacement exceeded the planned 15%. That immediately translated into stability issues. The immediate response was to add 40 tons of ballast in bulged on two sides. Teh trials resumed but still exhibited a large list when turning. We can imaging the cold shivers down to the spine of captains charged of this first serie of trials. Bulges were installed on both sides indeed to improve stability, a work completed in November 1933 on Chidori, that was transferred to the Sasebo Naval District and returned in reserve. In January 1934, she re-integrated the 21st Torpedo Squadron with Manazuru.

In March 1934, Tomozuru, capsized in heavy weather (72 men lost), whereas Chidori like her was in night attack training until canceled. Tatsuta, Chidori, and Tomozuru made it into Sasebo but not Tomozuru. It was Chidori’s captain that tried to contact and failed to spot Tomozuru and raised the alarm, contacting the command cruiser Tatsuta. She immediately went back and started a search, until ordered to return by Tatsuta given the still heavy weather. The investigation later blamed the poor design to Rear Admiral Fujimoto Kikuo that ordered it in the first place, whereas it clearly lacked stability. Improvements led Chidori to the drydock for extensive modifications. Hatsugane was still under construction, so she was modified before completion.

chidori
IJN Chidori in 1933 as completed

In the wake of the 4rth Fleet Incident in 1935, the class underwent another wave of improvements from August to November 1936. It seems they adressed further hull details, perhaps the replacement of their Type 91 HMG bty a 7.7 mm LMG, and speed went down to 27 knots, one less knot. In December 1936, the 21st Torpedo Squadron was created with all four sister boats. Chidori took its head and they were ordered to China. There, they took part in landing support and blockade operations. With the start of the Pacific War, Chidori took part in the invasion of the Philippines, and then was assigned convoy escort duties.

chidori

IJN Chidori in 1934

On January 14, 1943, she spotted the periscope of USS Pike off Cape Shionomisaki. She launched a depth charge attack but missed. On February 4 1944, she collided with the construction boat Sarushima, in Yokohama Port. Her hull needed repairs but instead immediately resumed its escort mission. She later arrived at Yokosuka for repairs, from December 23, 1944, leaving the drydock in the last days of the year. On November 16, 1944 (Showa 19), while escorting Convoy 4115, she detected a submarine east of Chichijima, launching 32 depth charges and claimed the kill given the oil slick and acoustic signature. By November 25, she joined the 3rd Maritime Escort Squadron, Yokosuka Naval District, in Tokyo Bay, Western Passage Force. She left Toba on December 21 and underway in escort when torpedoed by USS Tilefish (USS-307), west of Omaezaki by December 22. She sank with all hands.

IJN Manazuru (1933)

Manazuru was laid down at Fujinagata Shipyards on 22 December 1931, launched on 11 July 1933 and commissioned on 31 January 1934. She was modified from November 1934. She joined the Sasebo Naval District Register with Chidori in the 21st Torpedo Squadron. By March 1934 Tomozuru, capsized and the same day, Manazuru arrived at Terashima Strait, the designated assembly area for the same night raid training. She was saved from the storm as her condenser malfunctioned. Emergency repairs made on-site prevented her participation. Post-investigation, she was rebuilt. After the 4th Fleet Incident in 1935, the class went to a wave of further improvement from August to November 1936. By December 1936, the 21st Torpedo Division was sent to China, providing landing support and blockade operations. With the outbreak of the Pacific War in Decelber 1941 she initially supported the Philippines invasion and later concentrated on local convoy escort. Towards the end of the war, the lack of fuel saw her in longer inactive stances, she was stuck at Naha during an air raid on March 1, 1945. She was sunk by US aircraft carrier bombers, and later struck from the list on May 10.

IJN Tomozuru (1933)

Tomozuru was the third in class, laid down at Maizuru Naval Arsenal on 11 November 1932, she was launched on 1 October 1933 and commissioned on 24 February 1934. Modifications started in May 1935. Before that in February 1934, she joined the 21st Torpedo Flotilla at Sasebo. On 12 March 1934 she sailed from Sasebo for a night torpedo exercise with Tatsuta and her sister Chidori. At 03:25 in the midst of a storm, Tatsuta relaying orders, wanted the two Torpedo boats back to base. At 03:58 radio contact is lost with Tomozuru, possibly due to a loss of power. From 04:12 her lights are no longer spotted (notably by Shidori). In the next morning her disapperance is signalled to the command and the search starts, ambeit Chidori, at sea on her own search is recalled due to the still unstable heavy weather. At 14:05 a rescue plane discovers Tomozuru’s hull naked and drifting. On 13 March 1934, the cruiser Tatsuta spots and tow the TB back to Sasebo.

The capsizing of the ship was a mix of circumrstances, but should have not happened anyway. These ships, as small as they were, had a hull designed to deal with heavy seas and the captain knew the drills to go through high waves and strong winds conditions. Sothe design of the ship was soon brought forward. Plans were exhumed and a commission worked out a report, azfter audition of the 13 survivors. The instability of the Chidori, the result of cheating with treaties while playing with unrealistic tonnage and weapons combination was clearly to blame. At 600 tons having half the armament of a destroyer could work on paper, but some hard phylical laws could not be bent to the will. Weight was saved by a lighter construction, speed maintained by making the hull narrower, whereas the hull was massively top heavy due to the amount of artillery, torpedoes, a tall bridge and others percs.

Tomozuru 1934

Worst still, an enquiry towards the two shipyards involved revealed a lot of interpretations of the submitted design that led to a higher centre of gravity than feared due to a higher tonnage than expected. Efforts made to remedy this, albeit this started when the first shop in class was tried, with the adition of bulges. Chidori satisfied examiners and Tomozuru and her sisters that had their construction suspended, resumed. Tomozuru as seen above was both low on fuel or ammunitions, so crucial bottom weight was gone, whereas she had her full armament and complement, and there was apparently no way to compensate by using seawater ballast.

The commission concluded the capsizing due to a low metacentric height led the IJN committee inspecting the stability of all ships designed by Rear Admiral Kikuo Fujimoto, and named specifically for radical modifications the Aircraft carrier IJN Ryūjō, all four cuisers of the Mogami class, all the destroyers of the Fubuki, Akatsuki and Hatsuharu classes, submarine tender Taigei, the minelayers Yaeyama, Shirataka, Itsukushima, the entire Natsushima and Tsubame classes, the minesweepers of the No.1 and No.13 classesand even the subchasers of No.1 class. This was a colossal undertaking, that suddenly suspended work on many other constructions at the time, mobilized full ressources of many shipyards and cost many thousands skilled workers hours, adding to the already massive naval budget for Japan.

The incident severely challenged Japanese assumptions over stability, prompted a major review of all designs, with efforts going from reducing superstructures, armament, strenghtening the hull among others. In all cases, displacement rose and speed was reduced. Not only on older vessels, but also on all planned ships and those under construction at any level. The effort went on in 1934-36, even until 1939 in some case, notably for the Mogami-class. Back to Tomozuru, after her first, she had a second refit from August to November 1936. Details are unclear, it seems the issues were not as severe as those of other ships but like her sisters her weight cut back her speed to 27 knots. She followed her unit to China. When the Pacific Campaign started, like her sisters, she took part in the naval support force for the invasion of Netherlands New Guinea in April 1942, she was also at the Banda Straits in July 1942. Soon, her rear gun was landed, replaced by a twin Type 96 25mm AA gun tobolster her weak AA and gradually obained ten of those, mostly single mounts. She also carried up to 48 depht charges. She engaged in convoy escort operations until the end of the war.

One ionteresting cammpaign was over western New Guinea: On March 15, 1942 she joined the “N Invasion Force”, headed by the light cruiser Kinu, seaplane tender Chitose (before converison to carriers), and the destroyers Yukikaze and Tokitsukaze. The N Invasion Force assembled in Ambon and proceeded in the night of March 29, arriving on the early morning of March 30 to assemble at Manokwari on April 22 at the conclusion of the whole operation, then disbanded. The cruiser Isuzu was then formed into the the “S Invasion Force” for Operations on the Lesser Sunda Islands, including Tomozuru which arrived to her assembly point in Surabaya on May 7, departing the following day. She was back to Surabaya between May 21 and 25.

From January 2 to 5, 1943, the IJA Sugiura Detachment was carried from Ambon to the Aru Islands on the Kunitama Maru escorted by Tomozuru and Hatsugane. Tomozuru transported herself part of the Sugiura Detachment to the Kai Islands. Next she headed for Ambon, but was strafed and bombed en route, damaged by a near miss, (7 dead, 7 wounded). Her engine room and second boiler room were flooded and so she was towed by IJN Hatsugane untill reaching Ambon on the 12th for provisiononal repairs.

Tomozuru sinking

Much later with the U.S. invasion of Okinawa imminent, the IJN command detached her to the Nansei Islands for emergency transport. She departed Kagoshima on March 13, escorting the Kana 304 convoy, bound for Naha. On the 18th, TF 58 attacked Kyushu. She was ordered to retreat toward Sijiaoshan. En route, underway on the 24th, she was spotted by carrier aircraft that was absorbed into an air support near Okinawa, then sunk by the coordinated effort of several torpedo-bombers, in the East China Sea. She was struck from the Navy register on May 10.

IJN Hatsukari (1933)

Hatsukari

Hatsukari was laid down at Fujinagata Shipyards on 6 April 1933, launched on 19 December 1933 and commissioned on 15 July 1934. She was being fitted out when the Tomozuru Incident occurred on March 12, 1934. This halted construction pending the result of the investigation. Construction resumed with a revised design, so she was completed on July 15. Once commissioned, she was assigned to the 21st Torpedo Squadron, Sasebo Naval District. By September 1935 after the 4rth Fleet Incident she had further improvement work from August to November 1936. By December 1936 her unit was sent to China, for landing support and blockade operations and in WW2 she supported the southern invasion. From March to April 1942, she took part in the Western New Guinea Defense Campaign and then was tasked of convoy escort operations until the end of the war. In 1945 she was stuck in Hong Kong, that is until the surrender, captured, and then struck from the registry on May 3, 1947, scrapped on situ in 1948, the last survivor of her class.