An innovative light cruiser: Hiraga’s IJN Yūbari
Yūbari (夕張) was not only on the very first IJN post-WW1 design, but it was an experimental light cruiser which idea dated back from 1917 (where it was first programmed) and started in 1922, completed in 1923 for the Imperial Japanese Navy. Designed by famous engineer Hiraga, she was largely seen as a test bed for new designs and technologies and light tonnage in the midst of worldwide reductions, post-Washington. Nevertheless she was commissioned and quite active in many operations of World War II in the Pacific. Yūbari’s designs and innovation would find their way in many future IJN warships, from destroyers to cruisers. During the war she took part in the most vicious fights in the south pacific, notably the whole Solomons campaign, from beginning to the end at Rabaul in 1944. She was commanded in 1940-1942 by captain Masami Ban, until 1943 by Taiji Hirai, Morie Funaki until 1944 and in the end, Takeo Nara for two months.
The Tenryu on trials, 1919
In 1917, new wartime IJN cruisers designs meant for scouting, raiding and escort were well seated on the new model of the Tenryū. Prior to that the Chikuma class were merely a prewar design and the Tenryū was intended to be the blueprint, the prototype for whole series of cruisers of the 1918 and 1919 programmes, four of them, all very similar with up to ten shielded guns, generous torpedo armament, high speed and very light protection, and onboard aviation. They also doubled as destroyers leaders. However the last class, Sendai, laid down in February 1922, were to be a closing for this type of ships. The admiralty wanted to take a radical departure and explore new possibilities, notably in general arrangement of the artillery, new protections scheme, better speed and range, testing also an experimental machinery. The 1917 project was to be named initially IJN Ayase.
The experimental light cruiser was authorized under the 1917 8-4 Fleet Program. However funding was not available until 1921. Yūbari was to be a new generation scout cruiser, experimentally combining the same combat potential of the standard 5,000 t Sendai-class with a much lighter displacement. After Japan signed the Washington treaty and its tonnage limitations for cruisers, this made even greater sense. However, the experimental cruiser was a pre-Washington cruiser, tailored for IJN needs.
Captain Yuzuru Hiraga, Japan’s leading naval architect, gathered his team and started working on the blueprints. He was assisted by Lieutenant Commander Kikuo Fujimoto, and presented an innovative, influential design which was well remarked at the time. It laid down the philosophy for cruisers as well as destroyers, of more firepower for less displacement, pushed to the extreme on the Furutaka and Aoba classes, essentially heavy cruisers with a 7,000 tonnes displacement to take advantage of every tonne authorized by the treaty.
Design of the Yūbari
ONI booklet – Yubari for the USN
The basic design concept for the Yūbari was to push forward both speed and firepower, to the expanse of protection but also displacement. Weight saving measures included a drastic reduction of the armor, integrated directly into the hull structure, part of the side and deck, and a high forecastle with significant flare, in order to improve seakeeping characteristics. With just one truncated funnel, the profile of the new ship, much shorter, ended with a 2.890 tonnes displacement, half that of a Sendai class that was in construction at that time.
Yuzuru Hiraga succeeded in having a ship almost with half the displacement, but still armed with six 5.5 in (127 mm) guns, one less than the Sendai, and half the number of torpedo tubes, while protection was reduced from 2.5 in on the belt down to 2.3 in. Other figures were roughly similar, but both the “structural armour” and intensive use of welding reduced the tonnage. Simple maths showed how profitable it was to built a fleet of these, giving extra vessels for the same tonnage.
Hull and general characteristics
The IJN Yūbari was as small ship, but not that small for many light cruisers of WW2, which were of the same format: The hull was 435 feet long between perpendicular, 447 feet 10 inches at the waterline and 455 feet 8 inches overall. Its ratio was below 1/10 as she made 9 feet 6 inches in beam (versus 48 feet 5 in on the Sendai).
The bow reminded the Sendai in shape, but the forecastle started right aft of main bridge tower. To even save electrical cabling, batteries and associated electrical sub-systems, the hull was pierced of three levels of ports, the lower one just above the waterline, an obvious source of flooding. Their framing was welded shut.
Initial weight-saving measures were so extreme that Hiraga thought possible to target 2,700 tonnes unloaded. That was twice more than most destroyers of the time, but still very light for a cruiser. Eventually engineers were so fearful of structural weaknesses that some stiffening during completion was necessary, making the ship actually 13% heavier than planned, 419 tonnes more to be exact.
Also this caused an extra foot of draft, and 1.5 knots (2.8 km/h; 1.7 mph) speed reduction over the designed speed of 35.5 knots or even 37 as initially planned in 1921. Both very new new technologies, unproven sub-systems and procedures led to many mishaps and issues, becoming apparent once in service. The recognisable truncated smoke stack was too low and draw poorly. After completion and service it was revised, enlarged by 1.80 meters in 1924. Stability was also an issue, due to the narrowness and lightness of the hull, and Additional ballast was added for better stability.
The interesting point about it was Hiraga essentially scaled up a destroyer powerplant, with three turbine engines fed by eight oil-fired Kampon boilers for a total output as designed of 43,060 kW (57,740 hp). The exhaust pipes were trunked into a single smokestack, which freed deck space. This was a contrast to previous IJN cruiser designs like the Sendai and its four smokestacks. However this solution was not without causing problems: The draft was reduced, causing some overheating in the internals. Therefore during a refit, the funnel was heightened and widened.
These three turbo-gear units had a cubic capacity of 19,300 liters and developed some 14.2 Megawatts for 19,250 hp, a power passed on three-bladed propellers. These Parsons-type turbines developed by Mitsubishi under licence and and manufactured at Sasebo. The boilers were similar to those used on the Minekaze class destroyers, just double the number.
The Yubari in speed trials, 1923
The Layout was particular: Two power units were in the front and back of the engine room, which was 55 m in length, for a total area of 235 m². Each unit included two main turbines, with an active high pressure one at 3000 rpm, fed by a HP fuel pump, and a lower rate turbine for 2000 rpm used for reverse, but fed by the same high pressure fuel pump. The transmission used two leading gears rotating a 3.12-m shaft three-bladed propeller at 400 rpm. The reverse turbine used the same housing as the high pressure one, with no separate cruising turbines. The two forward cruising gears were turned off at full speed.
Fuel supply comprised 916 tons of fuel oil, stored located in the double hull, under the forward lower deck and on the sides of the first boiler room, also protecting it by absorbing a potential hull damage. This supply allowed the Yubari to extend her range to 5,000 nautical miles at 14 knots. It was however found on trials, that overheating the boilers to increase top speed for long periods of time massively increased consumption, down to 3,300 miles when fully loaded. This is to compare to the Minekaze class range of 3600 miles, making the Yubari useless when acting as destroyer leader.
The eight water tube boilers were of the Kampon Ro Guo type. They integrated an oil heating system according to some sources, and for others, comprised mixed boilers, installed for fearing oil shortages in case of war. They were located in three boiler rooms, two small ones forward (perhaps the mixed ones), four large ones in the middle section and two large aft. Working pressure was 18.3 kgf/cm² at 156°C (or 138°C according to other sources). A twin funnel exhaust was used, one for the first four boilers, trunked and connected in a large slope to the almost vertical aft funnel group. This was an idea of Fujimoto to reduce smoke polluting and obscuring the bridge, and making the silhouette smaller and lighter. However, as we saw alrady, the drag was insufficient, forcing to rework the funnel shape after commission.
Yubari performed her sea trials on July 5, 1923 off Kosikijima Island, and was tested with an ouptut of 62 336 liters, for a top speed of 34,786 knots as registered. This was less than the contracted speed of at 35.5 knots, but due to unanticipated of overload, 3463 tonnes versus 3141 standard as planned. This steam power was completed by an electrical power unit, a network working at a voltage of 110 V, comprising two 66 KW electric generators, powered by in turn by two internal combustion engines located in the engine room.
The main battery of Yubari consisted of six 14 cm/50 3rd Year Type naval guns, the same as the Sendai, but mounted in a very peculiar arrangement: Two twin gun turrets on superfiring positions fore and aft, and two single gun turrets on the deck. This inversion of weight (the dual turrets higher up were a problem for stability) nevertheless allowed the ship to fire three guns over the bow or stern, including two with a better field of fire.
Her six 140-mm Type 3 guns were developed before WWI, adopted by the IJN on April 24, 1914. The No.1 and 4 deck guns had armored shields (similar of those from standard 3500/5500-ton light cruisers). The twin closed turrets (No.2/3, type A (Ko) were initially developed for reconnaissance cruisers (1916 project and 1918 project). Apart IJN Yubari, they were installed on the IJN Dzingei and Tegei floating depots and the minelayer IJN Okinoshima. The 50-ton turret measured 5.5 m long, 3.4 m wide 2.46 m high, covered with HT steel plates, 10 mm in thickness. Electric traverse speed was 4° per second. Elevation was speed was 6° per second. Manual aiming backup was provided for emergency. All six guns were placed in the axis but there was little room available to elevation, so they could not be used for AA salvoes and fire was differed to avoid causing damage to the superstructures.
Ammunition for the main guns comprised 38 kg shells with 11 kg bagged charges. They were stored in safe rooms located on the hold deck, at both the ends. They were carried upwards by four bucket chain hoists, to bow forecastle level and aft upper deck. For the single mounts deck guns, loading was carried out manually through the central supply wells but with a higher rate of fire. When Yubari entered service, two types of shells were carried, the “general purpose” ballistic cap hard half-AP shell but also the standard high-explosive, and also an incendiary and flare type shells were also carried and tried in exercises. Maximum firing range at 30° max elevation was 19.1 km.
IJN Yubari, circa 1932
This was completed by a light artillery consisting of a single 8 cm/40 3rd Year Type dual purpose naval gun (AA), and two 7.7 mm machine guns for AA defense. Near the torpedo tubes were placed these 76.2 mm/40 type 3 AA gun elevating to 75°, completed by the two 7.7-mm Ryu machine guns. 76-mm shells were stored in the stern underdeck, placed right of the central propeller shaft. Two 47-mm signal guns of the Yamauchi design were located in the front superstructure.
It seems ludicrously inadequate for WW2 but in 1922, planes were still not considered a threat for ships and merely ways of doing reconnaissance. Many Type 3 heavy machine guns derived from the Hotchkiss 1914 model for the IJA could be carried also, and were, when the ship was transporting troops during wartime. The 7.7-mm Ryu machine guns were located amidships on a raised platform for anti-aircraft defense.
For closer engagement, notably night fighting the Japanese affectionate, IJN Yubari was fitted with two twin torpedo launchers banks placed on the centerline axis, fore and aft of the AA platform, just like in a destroyer, rather than side mounts like on the Sendai. The ship lost half its torpedo capability compared to the latter, but gained a 300° traverse and four reserve Type 93 torpedoes. The fire control system was centralized in the bridge, with no redundancy to save weight.
The twin rotary 610-mm torpedo tubes were of the type 8, similar to those of IJN Nagara and Sendai. Each weighted 8.45 tons, for a length of 8.8 m, 3.04 m width. They were powered by a 5 hp electric motor providing a traverse of 20° either side and were provided with manual loading backup. They launched a combined-cycle torpedo of the type 8. Eight were carried in all. Each weighted 2,362 tons and carried 346 kg of trinitrophenol explosive warhead charge. They could be set to 20,000 m range at 27 knots, or 15,000 m at 32 knots and 10,000 m at 38 knots. Placed on the upper deck, central part of the hull this allowed spare torpedoes to be easily accessed. Warheads were stored separately in a room located next to the central propeller shaft. Torpedoes were never fire at full speed due to heavy spray. The problem was solved by them higher, while shields were provided, shown in later pictures.
Control for the main guns depended from a type 13 central aiming visor placed on the tripod mast 23.06 m high. it used a synchronous transmission device developed on the basis of a WWI British prototype adopted by the Navy in 1916. Its effective range coincided with the main guns at 19 km. Two 2.5 or 3-meter Barr and Stoud rangefinders were also used, placed on the edges of the compass bridge. For night fighting, two 90-cm powerful lights projectors were carried, one located above the compass bridge, the second behind the funnel. They were put to good use at the battle of Kolombangara, illuminating USS Vincennes.
Least known, Yubari could also be used as a minelayer, carrying Type B mines, No.1 type, adopted by the IJN on September 2, 1921. They were an improved version of the No.1 Type A used since 1916. They had a cylinder diameter of 0.5 m, for a 1.07 m length, weighing 192 kg, carried 102 kg of trinitrophenol. Installed in pairs on the business end of a 100-meter steel cable, they detonated on contact. To protect them from the effects of blast gases from the stern main guns, they were covered by a casing, on six parallel mine deck rails.
That was certainly on paper the weak point of the design, at least compared to the previous cruisers, notably the Sendai class. IJN Yūbari was given 38 mm (1.50 in) plating for the belt, to protect the powerplant and the gun magazines, 28 mm (1.10 in) for the deck and bridge, but it was integrated directly into the structure, thus saving much weight and making an overall far better protection. The turrets had 25 mm thick frontal plating (0.98 in).
The main armor belt was composed of three rows of NVNC plates with a total length of 58.50 m, about 42% of the hull, for 4.15 m in height and the best thickness over the powerplant, located inside the hull. Its lower edge was connected to the double bottom edge starting from from the keel, and the upper one was connected to the armored deck. The belt had an internal slope of 10° but outwards, from top to bottom, not a good solution as the contact angle of incomng shells was close to perpendicular. On subsequent projects, plates were tilted inward. The outer lining of the High Tensile steel was 19 mm. The fuel oil tanks were located in between this internal section and the belt itself. The thick liquid provided an additional buffer agains vibrations caused by a round penetration, but a heavy cal. near-miss could rupture the internal layer.
The upper part of the armor belt was connected to a 25.4 mm armored deck, made of NVNC plates. The part between belt and outer casing was made of 22 mm thick HT steel plates, and 16 mm plates of the same additionally attached to the inner section. The lower funnel section and air intakes were protected by a 32 mm NVNC layer, up to 0.63 m of the armored deck. The superstructure was left unprotected but the turret wells, internal elevators, barbettes and interphone pipes were covered with HT steel thick eneough to deal with shrapnell. The overall picture, despite thinner plating in just one portion, was that Yubari had a significantly better protection than previous designs. The total armour weight was 349 tons, making 8.5% of the displacement versus 220–238 or 3.4–3.7% on the previous 5500-ton cruisers like the Sendai/Kuma-class and just 176 tonnes or 4.2% on 3500-ton cruisers, making it twice better than the Tenryu class in that respect.
The Yūbari in action
Yubari in sea trials, 1932
Early years: The interwar
IJN Yūbari, laid down on 5 June 1922, was launched on 5 March 1923, completed at Sasebo NyD, commissioned on 23 July 1923, just before the 1923 Great Kantō earthquake. She immdiately was sent to help evacuate refugees from Yokohama and other stricken cities, and on September 1923 was visited by Crown Prince Hirohito. In April 1925, she followed US Navy exercises off of Oahu, and taking part at last, she was chased by American destroyers but managed to left them out, impressing the guests present. Back home, she was versed to the reserves in November 1933.
In 1932, the Yubari’s single 76 mm AA gun was removed. In 1935, two twin Type 93 13.2 mm (0.52 in) guns were fitted, long derived from the Hotchkiss M1914. These were replaced in turn by two twin 25 mm guns in 1940.
Exactly one year afterwards, she left the reserved under Captain Tadashige Daigo command. She was assigned to the Yokosuka Naval District, modernized and refitted the next year. She spent 1935-36 patrolling patrols the Chinese coastal waters, and when the second Sino-Japanese War broke out in August 1937, she helped evacuating Japanese civilians of southern China. She received next the mission to cover landings of the IJA at Hangzhou, on 20 October 1937. Back to Yokosuka, she joined the reserved in December 1937, emergin in March 1939 to be sent to Ōminato Guard District and to the waters of the Sakhalin Islands, contested by USSR.
Yubari in Shanghai, 1937 – ONI
On December, 7, 1941 she served as flagship of the sixth Destroyer Squadron, 4th Fleet. This force was sent to defend the South Pacific Mandate in Truk. In early 1942, Yūbari served as flagship for the Japanese invasion force of Wake Island, she was coordinating and covering fire from 11 to 23 December 1941, proceeded to shore bombardment, while USMC island gun position replicated, but she took no apparent damage.
The Solomons Campaign: Rabaul & Salamaua
Yūbari and her destroyer group then took part in the capture of Rabaul and New Ireland in the Solomon Islands, and took part in the invasion of Salamaua–Lae on 8 March 1942. Two days later two Douglas SBD-3 Dauntless attacked her from USS Lexington. They missed, but they were so close, Yubari had many KiA among her AA gun crews. Next she repelled a wave of four Grumman F4F-3 Wildcat. They strafed her and killed her executive officer and other officers as the bridge was crippled.
The next day at dawn she was attacked this time by SBD-3s from USS Yorktown. The latter managed to hit gunpowder charges stored near the No. 2 turret. This detonated but the fire which spread rapidly was contained by the damage control crew which set protective mattresses around the bridge. A single F4F-3 managed to blow up gasoline drums in her port lifeboat, causing more fires. Fortunately for the ships, her direfighting teams were good, despite too short fire hose. Fire started to catch the forward torpedo mount but the captain ordered them fired in emergency. However, the mount did not moved, due to electric maulfunction. Then the crew managed to have them dumped to the sea by using pulleys and ropes while the fire was closing fast.
In total IJN Yūbari escape certain destruction, having evaded succesfully 67 bombs and 12 torpedoes, and only deplored 13 KiA and 49 injured. Later, four USAAF B-17 Flying Fortress were en route to Rabaul, found her and bombed her. She took four near-misses, from heavy bombs, blasting her stern with three large gashes. These were patched and the cruiser managed to sail to Truk for repairs until 25 March 1942.
Operation Mo May 1942
When Operation MO started on 4 May 1942, Yubari was again the flagship of the attack force and shelled positions. On 7 May, she was attacked again by a pack of four B-17, which missed again. She later managed to rescue survivors from the aircraft carrier Shōhō, sunk earlier this day. She was back to Truk on 13 May. She then learnt that operation Mo was cancelled because of the Battle of the Coral Sea mixed results. Worn out, she sailed for home, reaching Yokosuka for a short refit and maintenance lasting from 19 May to 19 June 1942 while her crew rested.
The Solomons Campaign: Guadalcanal
From 29 June 1942, IJN Yūbari was part of the force engaged in the Solomon Islands and took part in the whole campaign. She carried personnel on Guadalcanal which would construct an airfield, later widely contested. By 17 June however her chief mechanic signalled many problems with her powerplant. She was forced to never passed 26 knots (48 km/h; 30 mph) for safety, only usinf two shafts. The cruiser nevertheless was deemed fast enough to take part in the Battle of Savo Island which took place on 9 August 1942, where she managed to hit USS Ralph Talbot, a destroyer during this fateful night, while she torpedoed and hit the heavy cruiser USS Vincennes, one of the three sunk. This crippling blow forced USMC forces present to be deprived of their well-needed supplies, as the whole landing force fled the area. They would have to fend off Japanese attacks and their constant reinforcements in the Jungle for months.
On 20 August 1842, IJN Yūbari sortied from Truk to patrol up to the Marshall, Gilbert, and Palau islands. She was stationed at Tarawa from 20 October 1942. On 20 November she was still there as a guard ship, but departed for Yokosuka in late December. She was refitted there, her middle turbine repaired, while the decks received a number of additional much-needed AA guns. She was out in February 1943, and sailed for Rabaul. She arrived there on 1 April, tasked to the Southwest Area Fleet. On 2 July her destroyer attack group shelled Rendova Island where US Forces tried to consolidate a bridgehead.
While she was back off Buin in August 1943, IJN Yūbari struck a mine. Her bow was blasted and the forward hull twisted down, with 26 injured. Her speed fell to 22 knots due to the broken and twisted prow, but she managed to make it back to Yokosuka for repairs. This took until October 1943, but she received a complement of anti-aircraft guns. Also for the first time she received a Type 22 surface search radar plus a Type 94 sonar for ASW warfare.
Back to Rabaul – November-December 1943
She returned to Rabaul on 3 November. On 4 November, she made it in time to rescue 196 crew and infantry, and even manage to retrieve three field guns from the sinking transport Kiyosumi Maru, managing to stay afloat after the previous day air attack. Two days later, she se was part of the infamous “Tokyo Express” hich carried troops and supplies by night to Guadalcanal. She was carryong herself 700 men of the IJA 17th Division plus 25 tons of supplies, but to Bougainville Island.
On 11 November 1943, IJN Yūbari was attacked and damaged by planes for two carriers during a Raid on Rabaul an anchor. This happened again on 14 November, but each time she only had splinter damage from near-misses. A week later, she was to be part of another “tokyo Express”, this time to Garove Island (New Britain), cancelled after she was badly damaged by a raid of USAAF B-24 Liberators and Seaplanes PBY Catalinas (which could carry bombs). This forced her to return to Yokosuka on 19 December for long repairs. Like the previous time, the IJA pressed to add more AA batteries, which were installed wherever possible, as this was the main threat for the ship and many others in the IJN by that time. She had therefore her more significant refit as her two single deck 140 mm (5.5 in)/50 main guns were removed. They were replaced by a single Type 10 4.7 in (120 mm)/45 gun. Also six twin and one triple Type 96 25-mm AA guns were placed on the deck while a Type 22 search radar was installed on the mainmast, and two depth charge launchers at the stern for ASW warfare; Mine rails were not used anymore and she never performed a wartime mission of minelaying as far as the records shows.
Last operations, March-June 1944
On April 23–25, Yubari, teamed up with IJN Kinu and the destroyers Samidare and Yuzuki, to Palau, taking on board 365 soldiers and 50 tons of cargo. On the evening of the 26th she escorted the transport No. 149 to the island of Sonsorol. On the morning of April 27, the ships unloaded at destination and set sail around 9h00 AM.
On , and they refused to attempt to reach the cruiser to Palau, . “Yubari” sank at 10:15, leaving its nose under the water, this happened 35 nautical miles from the island of Sonsorol, at a point with coordinates 5 ° 38 ′ s. w. 131 ° 45 ′ in d.HGYAO. In total, 19 crew members died during torpedoing and the struggle for survivability  .
Yubari was back in action, heading for Saipan on 30 March 1944, and departed later for Palau on 25 April, sighted two days later the submersible USS Bluegill. Her captain had a lucky spot, as this was his very first war patrol. Well placed, he fired all six bow torpedoes from a range of 2400 meters. Yūbari’s spotters saw them, and she managed to evade four, but no the last two, which hit her starboard side, blasting N°1 boiler room. it was approximateiverly 10h04 AM.
The flood was so massive that bulkheads could not stop it and N°2 boiler room was soon flooded also. She lost speed and started to roll starboard while her bow plunged under. Only her middle boiler room and turbine remained safe, allowing the ship to move on, but this failed also. By 10:30, the safety teams worked hard but could not stop the flooding.
and even when the destroyer IJN Samidare tried to take her in tow at 16:50, at 5-knot speed and using anchor chains. But they burst after several attempts as Yubari was already too heavily loaded with seawater.
Nevertheless, with many air pockets she managed to stay afloat almost 24 hours after the torpedo hits. On April 28, at 4:15 AM, water reached the upper deck and later her captain ordered to abandon ship. Noon came, and she finally sank at 05°20′N 132°16′E, around 10h15 AM. She lost 19 crewmen, mostly stokers killed during the torpedo hits and trapped inside by the flooding. However Yubari was not stricken before 10 June 1944.
HD illustration of the Yubari in 1923 and 1942 by the author, 1/200
Displacement 3,315 t. standard -4,447 t. Full Load
Dimensions 139 m long, 12 m wide, 3.6 m draft
Propulsion 3 shaft turbines and 8 boilers, 57,500 hp, 34 knots
Armor: Armored Deck and belt 16-22-25-28 mm, gun shields 11 mm, ammo wells 32 mm
Armament: 6x 140 mm (2×2, 2×1), 1× 76mm/40 AA, 2×2 610 mm TTs, 2x 7.7mm MGs, 34 mines.
WoW’s rendition of IJN Yubari
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Tamiya 1/700 WL series