Yashima Class Battleship:
Developement and planning of a new capital ship for Koko no Kaigun started on the sly in early 1934, after the Diet had passed the first Rearmament Bill. First drafts took off from some of the early 20s designs that had been shelved because of the Washington Naval Treaty. The 28,5-knot ones armed with eight and ten 409mm (16.1-inch) guns were immediately discarded as inferior to that of the Amagi and the cheating Kii Class,. Focus was thus shifted to the twelve-gunned 409mm design, the last approved and ordered before the WNT, and the early draft for a Battleship armed with six 460mm (18.1-inch) guns in twin turrets. At that time, the only requirement already set was a top speed of 30 knots, to allow the new battleship, if eventually built, to operate jointly with the Amagi and the two Kiis.
The 12x409mm design was the first to progress into the planning stage. By mid 1935 it called for a 52.600ton ship at standard load, 259,6m long, 35m abeam with a draft of 9,5m. 360mm belt armor, 178mm decks, 76mm bulkheads and an endurance of 7.900 nautical miles at 16knots. Secondary armament was to be made of twelve guns, either 152 (6-inch) or 155mm (6.1-inch), augmented by eight 127mm (5-inch) ones. Design for the 6x460mm-gunned ship was less advanced, but called for similar specifications except for a secondary armament of fifteen guns.
Koko's denunciation of the naval treaties changed the tables, shifting the design efforts towards the heavier gunned ships. Developement of a 460mm gun, suitably labeled 40cm/45 Type96 started in 1936 after the second Rearmament Bill passed by Morimoto's government. The Bill also approved construction of a new class of four Battleship. Following similar plans as the Japanese to give the fleet some edge over the USN and RN by building superior ships to counter numerical disatvantage designers ditched completely the 409mm-gunned design focusing solely on the 460mm one. Despite this, the Naval Staff was not satisfied with a main armament of just six 460mm guns, so a fourth twin turret was added, bringing the main battery to eight barrels. To counter the increased weight, maintaining the planned endurance and speed and thus make space for the extra main guns, the hull was lenghtened by over 20 meters and the fifth 152mm gun turret -to be placed on centerline aft, superfiring the 460mm one- was deleted entierely. Design was finalized by fall 1936, and the lead ship started construction on October 14th of the same year at Toumachi Naval Arsenal. She recieved the name Yashima a few weeks later, her sisters were to be called Suruga, Omi and Mikawa.
Yashima's construction went on in deep secrecy -just like that of the Yamato in Japan- until her launch, on September 29th 1938, 23 months after she was laid down. Fitting out lasted for another 15 months. Yashima was commissioned as the new Koko no Kaigun Flagship on December 1st 1939, starting her trials immediately after. Despite the war in Europe was already raging since two months secretness around the newly built ship remained high. Especially, the Naval Staff accuratley avoided having any of the Kii class ships or the Amagi sitting in port or operating together with Yashima. The reason was obvious, since during her tortuous design phase the new Battleship had grown to massive dimensions.
At 281,95meters (925feet, 1inch) in overal lenght she was the longest warship ever built by any navy up to that point, dwarfing any other warship -beign Carriers, Battleships or battlecruisers- by at least 11 meters (36 feet, 1 inch). Her waterline lenght was 276,01meters (905feet, 6inches), her beam 35 meters (114 feet, 10 inches) and her draft 10,6 meters (34 feet, 9 inches) for a standard displacement of 56.425 Tons and a full load one of 62.727.
Compared to the earlier drafts, belt armor was increased to 409mm (16.1inch) of thickness, angled inwards by 10° with 270mm (10.6inch) angled bulkheads connecting the citadel ends to the main gun barbettes. Anti-torpedo bulkheads were also strenghtened to 112mm (4.4inch) while decks were left at 178mm (7inch). Steering gear was enclosed in a 200mm (7.9inch) box, with the quarterdeck also protected by 50mm (2.2inch) steel plates, a lighter 30mm (1.2inch) protection was also given to the foredeck up to the anchor capstans. Main guns were protected by 540mm (21.3inch) thick plates on face, 236mm (9.3inch) on sides and roof and 409mm (16.1inch) barbettes. Secondary guns had 50mm (2.2inch) faces and 25mm (1.inch) roofs, sides and barbettes. The conning tower was protected by 500mm (19.7inch) thick steel plates.
Yashima main gun battery consisted of eight 460mm (18.1-inch) 45 caliber guns in four twin turrets. Almost identical in specification to the Guns of the Battleship Yamato, developed during the same timeframe, they had a maximum elevation of 43° and could fire 1.360kg (2.998lbs) standard and 1.460kg (3.219lbs) armour piercing shells at a maximum range of 41.780m (45.790yards), with a rate of fire of roughly 2 shots per minute, and 100 shells carried for each gun. Secondary armament was made up by four triple 152mm (6-inch) turrets, originally intended to arm the Senjo Class Cruisers before it was decided to convert them from CL to CAs. Fitted two on each beam, abaft the fore and aft superstructure, those 60-caliber guns fired 45,6kg (100lbs) shells up to 26.890m (29.414yards) away. They had a maximum elevation of 45° and a 6-round per minute rate of fire. 165 shells were carried for each gun. The main anti-aircraft weapon was the ubiquitous 127mm (5-inch) twin gun mount, their number increased from eight to twelve and fitted at midship in raised platforms. The guns were also shielded to offer further protection to the crew from the blast of the 460mm guns firing. They could elevate up to 90° and fire 23,45kg (51,7lbs) shells up to 14.800m (16.185 yards) with an effective AA ceiling of 9.400m (30.840feet) at 75° elevation. 300 rounds were carried for each gun. Light AA armament was made up by eight triple 25mm machine guns for a total of 24 barrels.
Fire control for the main guns was provided by a 15-m rangefinder and director set fitted on top of the massive forward pagoda tower, with a backup director fitted on the aft superstructure. There were also two 4,5m rangefinder for the secondary guns fire-control located on the forward superstrucutre, and four combined HA director-rangefinder sets for the 127mm anti-aircraft fire: two on each side abaft the funnel and another two on the aft superstructure. Four searchlight and four machine-gun directors were also fitted, in addition to an 1,5m navigation rangefinder forward and an auxiliary lookout station on the aft superstrucutre. The searchlight themselves were four 110cm models fitted on platforms around the funnel, above one of the HA director sets. The ship could operate two seaplanes, Nakajima E8N, thanks to a collapsible crane and a catapult fitted at the stern. A small maintenance hangar located between the catapult itself and the aft 460mm guns could house a third dismantled seaplane.
Engine-wise, twelve oil-firing boilers powered four steame turbines generating 167.522shp, driving four three bladed propellers. Coupled with the elongated hull lines and the specifically designed bulbous bow, the engines pushed the ship with ease to the intended top speed of 30knots. Thanks to a 6.300t bunkerage, endurance was 8.100 nautical miles at a cruising speed of 16knots, roughly 200 miles more than the original design.
Complement for the Yashima was 2.363 officers and men. As flasgship this rose to 2.489.
However, a few shortcomings in the design could be easily noticed: the choice of increasing the main gun barrels by adding a fourth twin turret instead of switching to triple mounts led to a very long citadel to protect her vitals, other than sporting one less gun than the soon to be launched IJN Yamato despite a hull that was almost 19meters (62 feet, 5 inches) longer. Negating the advantage of the thighter beam and the 10.000t less in displacement when compared to the Yamato. The placement of the secondary battery also allowed to a broadside of just six guns, instead of the nine-gun one of the Yamato. Uknown to anyone at the time, the ships also shared with Yamato the faulty designed joint between the armor belt and the anti-torpedo bulkhead. Yashima's sea trails were not exempt from problems either. Quickly demostrating that despite previous testing and precautions Koko no Kaigun naval designers had underestimated the effects of the blast pressure from the 460mm guns. During the first gunnery trial windows of the lower bridge level were smashed when the ship fired a full broadside. Portholes on the superstrucure went to pieces and the seaplane was almost blasted overboard when the second salvo was fired three quarters to the stern. Gun blast interference was also reported limiting the 127 and 25mm guns utilization. Damage to the shipboard boats was also feared if the aft guns fired to port or starboard trained fully towards the bow and at maximum elevation.
To adress the Issues, Yashima was placed in reserve in February 1940 -Kii replacing her as Koko no Kaigun Flagship- and thoroughly refitted. Most portholes on the superstructure were closed over and the various forward tower greenhouses reduced, often replacing the glass panels with smaller and thicker ones. Many openings recieved blast shields to be closed when the main battery was to fire. All 127mm and 25mm guns recieved fully enclosed shields to allow their crew to man them even when the 460mm guns were firing. Small blast shield were added to protect the outer boat decks and the lower bridge walkways. The lower anti-aricraft platform up on the bridge was also partially enclosed. Many ventilation ducts to the lower decks were modified and trunked to make them less susceptible to blast pressure. Finally, a large part of the upper two decks fo the quarterdeck were gutted, expanding the original small maintenance hangar enought to house two fully assembled seaplanes. While this allowed to safely carry three seaplanes -or even four with one on the catapult as long as the main guns didn't fire- it forced a reorganization of the aft living quarters, decidedly worsening crew accomodation given the reduced available space. Initial plans to relocate aircraft facilites at midship were quickly dismissed because of space constraints, interference with the cranes and boat handling, the presence of the very same maintenance hangar at the stern and the fact that seaplanes would be still exposed to blast damage. Yashima joined again the active fleet in June 1940, when her refit was finally completed, but her teething problems had not made her very popular within cadets and crews. Beign assigned to Sentai 1 with Amagi, the most popular ship of the fleet, until late 1941 did not helped either.
Meanwhile, construction of the other three sisters went on. Suruga was the second ship to be ordered, but had to wait for her sister to be launched before construction could start. So the third sister, Omi, was actually laid down before her. Suruga was laid down at toumachi Naval Arsenal on October 19th 1938, launched 26 months after on December 8th 1940 and commissioned another 11 months later on november 16th 1941. Omi was laid down at Kousaten Navy Yard on june 4th 1937, launched in 28 months on October 7th 1939 and finally commissioned after lenghty 25 months on november 8th 1941. Both ships were modified during construction to address all issues that had emerged during Yashima sea trails. Having been laid down earlier, Omi was much more advanced and already fitting out, thus needing a much longer time to implement the modifications. Suruga instead had yet to be launched, so that she could implement all modifications with ease, resulting in a building time of 16 months less than that of Omi.
Compared to Yashima the two ships further reduced the size of the bridge greenhouses, the fore superstrucutre was more enclosed, blast shields were larger and the ventilation systems were more efficently trunked. The 127mm guns recieved newer shields and the searchlight platform was completely redesigned to offer better protection to the equipment, which also saw newer 130cm searclights replacing the earlier 110cm ones. The engine room ventilation system was completely rerouted, freeing space at midship to fit two small enclosed hangars for the ship's 9m whaleboats. The main boat deck was also protected from blast pressure by much bigger plates and was now served by a single centerline crane instead of two like on Yashima. The tripod mainmast was also replaced by a pole one, with a different starfish. The entire fire-control suite was modified, with the addition of a more advanced Type98 main gun director that was also fitted on the Japanese Yamato class. A full composite director/rangefinder set with 10m optics was fitted on the aft superstrucutre in place of the simple backup director of the Yashima. The 4,5m rangefinders for the secondary guns, the combined HA rangefinder/director for the 127mm guns and the searchlight controller were also of a newer model. The seaplane complement was also updated to two mistubishi F1M and a single Nakajima E8N.
Suruga and Omi looked identical upon commissioning, and were assigned to sentai 1 joining their sister Yashima. With Omi becoming Koko no Kaigun flagship after beign commissioned.
On December 4th 1941 the three completed sisters sailed from Toumachi for the planned attack against Midway Island. During the subsequent battle they first gave anti-air support to Umineko, Ahodori and Fukuro during the carrier action of December 7th against Midway land-based planes and the airwing of the USS Lexington, then they moved together with Amagi, Kii and Owari for a bombarding mission of the American atoll, paving the way for the amphibious landings that followed soon after. After the fall of Midway the three battleship kept operating with Koko's Carrier force along the western Hawaiian islands chain but saw no action until Arpil 1942, when they took part in the hunt for the Doolitle Raid ships, although they eventually failed to make contact with the enemy.
Later the same month, the new Koko no Kaigun Commander in Chief , Admiral Karasawa, oddly choose Yashima as the new Fleet Flagship in place of Omi. He later stated in a post-war interview that the Battleship still suffered from some shortcomings that had non been resolved during her refit, thus not beign a completely satisfactory fighting unit as her sisters Suruga and Omi were. Acting as the Fleet Flagship would have kept her out of minor operations, preventing unnecessary strains for the ship and crew. However, this also led to unwanted consequences during the next two years.
Yashima, Suruga and Omi took the seas again in June 1942, beign part of Yamamoto's Main body Fleet during the joint Operation AL/MI. Due to the unsubstantial contribution of the Japanese and Kokoan surface fleet during the Battle Off Midway, the three Battleships returned home without having fired a single shot. Their uneventful life continued until late October 1942. Suruga and Omi had took part in harmless patrols with Kokoan Carrier fleet around Midway, while Yashima had spent the previous four months berthed at Toumachi Bay.
Yashima, Suruga and Omi then departed for the Solomon Islands to support Japanese operations. The night between November 21th and 22th the joint Kokoan/Japanese, composed by six battleships, six heavy cruisers, three light cruisers and numerous destroyers engaged an USN fleet composed by five battleships, three battlecruisers, three heavy cruisers, four light cruisers and many destroyers. The americans were further baked by the Recherche Battleship HMRS Audacious and her escorts.
Suruga, steaming on the right column of the Japanese/Kokoan formation engaged Audacious herself and the South Dakota Class Battleship USS Indiana. Despite enjoing a superior battery of 460mm guns compared to the indiana 406mm (16-inch) and Audacious 356mm (14-inch) ones, Suruga suffered from the more accurate fire coming from the enemy units, beign struck by twenty-three main gun shells from Indiana and another fifteen by Audacious, while dealing seventeen hits in return to the former and nine to the latter. The exchange of fire effectively put out of action both Indiana and Suruga. As they both disengaged a damaged but still battleworthy Audacious kept hitting the Kokoan battleship, striking her another thirteen times before beign forced to stop the chase to avoid a torpedo spread fired by the Light Cruiser Ayase. Suruga left the battle with her superfiring forward turret jammed, a 7° list to starboard, four boiler rooms flooded, one seaplane shot down, the entire starboard secondary battery unusable and a large fire engulfing her aft superstructure.
Yashima and Omi slugged out with the Battleships Maryland, New Mexico and Mississippi. Yashima's gunnery was reportedly beign poor, with only four hits recorded on the USS mississippi during the entire course of the engagement. Yashima was in turn hit seven times, although suffering minor damage. Omi featured decidedly better, despite having recieved a direct hit from Maryland early on that knocked out the aft main gun director. The Kokoan battleship hit Maryland nine times with three salvoes, before switching fire to New Mexico, hitting the unlucky American ship with no less than twenty-six shells, making her an easy target for Ayase's torpedoes late in the battle. Omi later exhanged a few more shots with Maryland but with less success, suprisingly the American Battleship did not enyojed a great battle too, hittin Omi just two more times.
With victory achieved the Kokoan fleet took the chance to assess the damage and draw conclusions on the first ship-to ship engagement of their most powerful battlewagons. Yashima's performance was lackuster, further cementing the shabby reputation the ship had made for herself. Omi was instead more than satisfactory. She more or less engaged and put out of action two enemey Battleships while suffering negiglible damage in return, paying off the concept she was built on. Even Suruga's actions despite the massive damage suffered were considered positively, the ship had engaged two units and had suffered a staggering fifty-one main caliber hits and was still beign able to retreat from the battle under her own power. Although, admittedly, she had been somewhat lucky as very few of those shell had hit below the waterline, as mostly ridled the uperstructure.
Yashima and Omi were repaired and brought back to service within a month, while Suruga needed more extensive repairs than took her off the field until early June 1943.
Yashima and Omi were deployed again in March 1943, supporting the planned invasion of Espiritu Santo. After the inconclusive Carrier battle that followed forced the operation to be postponed the ships sailed back to Truk, where they remained until early July. By that time renewed American presence in the Aleutians and the French Frigate Shoals dictated their return to Toumachi.
On August 1st 1943, all three took part in the Battle off the frigate shoals (also known as battle of Gardner), durig which -by a stroke of luck between the numerous carrier attack runs- they managed to exchange a few shots with the retrating USS New York. As it happened earlier, Yashima greener and less battle-ready crew scored no hits, while Suruga claimed four and Omi two before the ship lost track of the slower enemy Battleship in a rain squall. New York was eventually sunk the day after by Kokoan carrier-based planes.
Meanwhile, The fourth Yashima Class ship had not been commissioned yet. Mikawa had been laid down on March 5th 1939 on a newly opened slipway at Toumachi Naval Arsenal. Works on her were initially scheduled to last 25/26 months until launch, planned for April or May, 1941. By hat time, however, Resources and manpower had started to been diverted to Light Cruisers, Destroyers and Submarines as a war in the Pacific was deemed more and more imminent. Launch was thus delayed until January 11th 1942, 34 months after Mikawa had been laid down. Further design changes over Omi and Suruga beign also partly responsible. Fitting out started to drag out too: after the Midway defeat had devoided the IJN of most of it's carriers it was briefly contemplated to convert Mikawa into an Aircraft Carrier, but instead of what was done in Japan with Shinano, Koko no Kaigun Naval Staff deemed the idea a waste of time and resources as a Carrier built up to from the ground would have been quicker and less expensive to be completed. Further delays were caused by the repairs needed by Suruga after the Third Naval Battle of Guadalcanal, which deducted more personnel from Mikawa's fitting out. As the ship had fallen behind schedule, Further modifications were planned to keep her fire-control systems up to date, ironically leading to further delays. Finaly, it was decided to fit her with Thiarian fire-control systems which had been just obtained during a technology exchange carried out by the submarine Ki-33. Planned to be commissioned by August 1942, and by April 1943 later, Mikawa did not join the fleet until December 27th 1943, a staggering 57 months after beign laid down and 16 months later than initially planned. Even the lead ship of the following Nakamori Class had endered service before her.
As commissioned, Mikawa featured and improved main gun rangefinder and director set, fitted with the Thiarian R1CD fire-control radar. She also sported the R2FA air search radar and the R4CA high-angle fire-control radar on her anti-air battery directors. For the surface-search equipment, designers chose to stick to the newer indigenous Type22 surface search set, although featuring an experimental improved recieving horn.
Overall, Mikawa was completed sporting less portholes on the hull than her previous sisters, the machine-gun directors were of an improved model, with an extra set on centerline above the bridge in place of an earlier lookout station. The 25mm suite had also been increased to 36 barrels by adding four more triple mounts at midship. The ventilation system was further improved, leading to more trunked cowls and a different boat stowage at midship with a smaller hangar and better protected boats, whose number was also reduced compared to Yashima, Suruga and Omi.
A new deckhouse was added at midship below the searchlight platform and anti-air director, housing more rooms for fire-control duties. The mainmast was of a further modified design, with a more compact appearance that improved anti-air gun arcs. Scupper pipes had been modified too, and an Aichi E13A had replaced the Nakajima E8N in the ships reconnaissance airwing.
In January 1944, shortly after completing her sea trails, Mikawa replaced Yashima as Koko no Kaigun flagship.
Finally serving as a Sentai of four, the Yashimas experienced a quiet first half of the year. The loss of two Battleship -Nakamori in January and Yagumo in February 1944- in a little more than a month had led Koko no Kaigun higer ups to avoid sending their largest battleships to take part in minor operation, preferring to save them for some future larger battles, eventually starting to think exaclty like the Japanese had always done with the Yamato Class units. The four sisters eventually sortied to screen the Carrier Force at the Battle off Laysian on May 15th 1944. After the indecisive battle they sat at anchor again recieving some wartime refits between June and August 1944.
Yashima was the first to enter the yards: she had many of her lower decks portholes sealed over to increase watertight integrity, the Airwing was finally upgraded from three Nakajima E8N to two Mitsubishi F1M and one Aichi E13A. The anti-aircraft suite was increased to thirty triple and twenty single 25mm machine guns, for a total of 110 barrels. Eight new machine gun directors were added, four in place of two searchlights and their director sets, two abaft the mainmast and two in place of the forward and aft lookout posts. The Type21 and 13 air search radars and Type22 surface search radars were also added as no spare Thiarian systems were available for her at the moment.
As soon as her refit was completed Yashima was detached from Sentai 1 and sent to Truk to act as the flagship of the Southern fleet, comprising all Koko no Kaigun ships still operating around the Solomon Islands. Suruga, Omi and Mikawa continued to be stationed in Toumachi Bay until they sailed on again in early September escorting Koko no Kaigun Carrier fleet for another sortie against the US Navy. What was later known as the Second Battle of Midway ended up as a disaster for Koko, with the Light Carriers Ahodori, Tobuio and the fleet Carrier Inuwashi beign sunk. The battleships escaped almost unscathered, only suffering light damage from strafing and near misses by enemy planes.
Following the battle it was decided to recall Yashima to Koko, so the Battleship left Truk on September 19th evening. Three days later, at dawn of the 22nd she was roughly 105 miles south of Nanto Island when the lone battleship, escorted by three Destroyers was sighted by the USS Archerfish (SS-311). The American Submarine quickly moved into position and launched a spread of six torpedoes before crash-diving to avoid possible depth charge attacks from the escorting ships. Possibly caused by the lack of training during Yashima long inactive streaks, or by inconscously lowering attention given the close end of the voyage in supposedly safe waters, reaction from the Battleship crew was late. Yasima failed to manouver in time and, despite a last minute hard turn to starboard, all six torpedoes from Archerfish found their mark. The first hit 32 meters (105 feet) from the stern, below the aircraft hangar. The second hit where the starboard outboard propeller shaft entered the hull and the third hit the shaft compartment that led to the engine room, causing widespread flooding. The fourth, fifth and sitxh respectively hit and flooded boiler rooms No.9, 6 and 3.
Yashima immediately took a 10° list to starboard, slowing to a near halt, both starboard engine rooms flooded quickly, leading to a loss of power to both the starboard propellers. Counterflooding on the port side was immediately implemented but the list kept growing, reaching 15° in the next 10 minutes. Still largely unknown to Yashima's crew was the extent of damage dealt by Archerfish. 4 out of six torpedoes had detonated between 3 and 4,5 meters below the waterline all hitting roughly where the joint between the main belt and the topedo bulkheads was located. The torpedo detonation dislodged the joint causing structural failures that greately increased the damage suffered. In boiler room No.6 the explosion dislodged an I-beam that punctured the bulkhead, causing flooding to the No.5 boiler room as well. The worst damage howevr was towards the stern, where the torpedoes had hit the starboard outboard propeller, the explosion had bent the shaft and cracked the encasing, weakening the structural integrity of the entire system.
By 7:15 AM, roughly an hour after the torpedo hits, Yashimas crew had managed to reduce the list to 12°. Powered only by her port propellers, Yashima turned north making 10 knots trying to reach Nanto. Half an hour later the list had further decreased to 10° and the speed could be raised to 13 knots after the inboard starboard propeller was restarted by pumping water out of the engine rooms.
At 9:00 AM the list had slowly increased again to 13° and speed was dropped to 10 knots as a precaution. The Battleship limped forward for another three hours. By that time she had sailed for 53 miles since suffering the torpedo hits. After that, just past 12:00, a sudden inrush of water caused the starboard engine rooms to flood again and the list increased to 20° within minutes. Strained by the prolonged vibrations and water pressure caused by the Battleship movement, the outboard propeller shaft had snapped dislodging intself from the ships and inflicting further damaged as it slipped out of the hull, tearing more bulkheads and spreading the flooding. The crew desperately tried to counter by flooding boiler rooms No.1, 4 and 7 but to no avail, as they only managed to slow the rate at which the list increased. For another two hours the crew battled desperately to save the ship. The destroyers attempted to take the Battleship in tow but the cables snapped two times. Around 2:00 PM the ship suddenly lost all power as the list reached 28°, at which point the valves of the port trimming tanks rose above the waterline and became ineffective. With the massive superstructure now looming above the water, threathening to further destabilize the ship, Yashima's Captain, Seto Hayami, gave the order to abandon ship at 2:18PM, the list now reaching 34°. At 2:57PM, eight hours and 42 minutes after beign torpedoed, Yashima rolled over and sank stern first 45 miles south of Nanto, taking with her 1.541 of her crew of 2.621, including Captain Seto, who refuesed to leave his post on the Battleship bridge. To date, Yashima remains as the largest ship ever to be sunk by a Submarine.
The sinking of Yashima came as a shock news for Koko no Kaigun. It happened very close to the home islands, in supposedly safe waters, revealing the deficency of the Kaigun coastal patrol service to ensure protection of it's own fleet. After a few weeks of turmoil through the Navy, during which most major units were kept in port, patrol schedules were reorganized, increasing both air and naval ones, and, with the exception fo the Hevy Cruiser Teji, lost near Midway in November, no major units were lost around Kokoan waters for more than a year.
A last reason of concern, and controversy, was the finding that an IJA convoy, en route to Toumachi on it's way to reach the Aleutians, had actually sighted an enemy Submarine the night before Yashima's sinking, but had deliberately avoided to relay the sighting to Kokoan units operating nearby. While it could have still been debatable that no comunciations were made at sea with the fear of disclosing the convoy position to other enemy Submarines, it was also true that no mention of the sighting was made even when the IJA transports docked at Toumachi for refueling operations.
In light of of a bleaching wartime situation coupled with growing distrust towards the Imperial Japanese army collaborations, the three surviving Battleships, Suruga, Omi and Mikawa, spent the next nine months training in home waters as to keep them out of harm's way.
During the same timeframe all three ships recieved a further refit: the faulty joint between the belt armor and the torpedo bulkhead was strenghtened, almost all portholes on the hull were closed and the anti-aircraft suite was increased to 48 triple and eight single 25mm machine guns, totaling 152 barrels. Two searchlight were removed and replaced with two 28-barrel anti-air rocket launchers. Crew rose to 2.747 officers and men. Omi and suruga were fitted with Thiarian R1CD fire-control radar and more advanced R12CAD high-angle fire-control radar for anti-air battery directors. The main air-search set was a Kokoan mattress system based on the Thiarian R7FA air-search radar, dubbed Type24, which supplemented the indigenous Type21 arrays fitted on the forward rangefinder arms. They were also the first Kokoan capital ships to be fitted with the Type33-kai surface radar, which could double as a fire-control unit if needed. Mikawa only recieved the Type33 unit, retaining her other former systems. The boat complement was further reduced on all ships, leading to the removal of the midship boat hangar, turned into anti-aircraft crew ready rooms and quarters. The ships also landed their remaining Nakajima E8N and Aichi E13A, replaced with the more advanced Aichi E16A. Finally, all three were given a blue-black paint scheme for night operations.
In this guise the three ships joined the enormous Kokoan/Japanese fleet at the Battle of the Philippine Sea. Their contribution to the battle was nothing exceptional but theiy did their job of shooting down some enemy planes with their anti-aircraftt fire.
After another four months in koko, duing which they saw nothing but training, Suruga, Omi and Mikawa departed for Brunei, where they joined the Japanese Center Force led by Vice Admiral Takeo Kurita. On October 22nd the fleet left the anchorage bound for leyte. The enormous formation was strong of fourteen Battleships, fifteen heavy cruisers, six light cruisers and twenty-three destroyers. After surviving unscathered a submarine ambush the night between the 22 and 23rd the Center force ships were repatedly attacked by US Carrier-based planed for most of the 24th . During the attacks, the Battleship Kirishima was sunk and the heavy cruiser Myoko forced to retreat after suffering heavy damage. Coordinated anti-aircraft fire had kept most of the other ships out of harm, so that no other unit was seriously damaged. Omi had escaped the attack with no damage at all, Suruga had suffered a single bomb hit on the warterdeck and Mikawa had been the subject of a few strafing runs from American planes. After detaching four Destroyers to assist Myoko and recover the survivors from Kirishima, Kurita feinted a retreat, then reversed course, crossing the San Bernardino Strait unmolested during the night.
The morning of October 25th the Center Force took by surprise the US escort carrier groups that were guarding leyte Gulf. As the Japanese engaged Taffy 3,the Kokoan charged Taffy 2. With Mikawa leading the Battleship line, all heavy guns openend fire against the escort carriers. While the 460mm (18.1inch) shells were so powerful that they actually wne through from side to sideof the unarmoured escort carriers, they still managed to inflict some damage, which coupled whit that done by the other Kokoan units, forced the US ships to slow down. As the cruisers moved in to finish the job the Kokoan fleet came under air attack from Taffy1 the third escort carrier group stationed at Leyte and the only one non directly engaged by eaither the Kokoans or the Japanese. The air-attacks at first were just a mere nuisance for the three Yashimas, but they bought enought time to allow the Thiarian Battleship Atharta – part of a co-belligerant fleet assembled after Thiarian surrender now escorting the American jeep carriers- to close in and open fire against Suruga. Enemy aircraft were busy giving the coup de grace to the crippled cruiser Chichibu, but this did not help the Kokoan battleship against the extremely accurate fire put up by Atharta, which scored a staggering fifteen hits out of eighteen shells fired just with her first two salvoes. Suruga suffered one boiler room floded, the forward sarboard 152mm gun was temporarily jammed, one of the searchlights was shot off cleanly. Another shell hit the superstructure just above the bridge, sending a rain of srapnels into the operation room below. Two further hits penetrated above the engine rooms, leading to a loss of power to the inboard starboard propeller shaft. More hits ad miship started a fire and one last shell penetrated the aircraft hangar at the stern setting a dismantled seaplane on fire. Suruga attempted to return fire but experienced malfunctions with her fire-control system and failed to score more than a few hits, suffering in turn another eleven hits by Atharta next three salvoes, causing a jam in her forward main gun turrets. Luckily for Suruga's survival, Athartha uncontested attack was short live, as after having spread havok between Taffy2 escort carriers the Kokoan Battleships, Amagi, Kii, Omi and Mikawa turned their attention to Atharta, hitting her sixteen times in quick succession. Clearly outnumbered and outgunned the Thiarian Battleship had no other option than retreating, not before suffering three more hits from Amagi.
At that point of the battle Suruga disengaged from the rest of the fleet and headed northwest at slow speed, assisted by two Destroyers, as the crew attempted to put out the fires and repair the jammed guns. Mikawa and Omi instead turned to the southwest along with the rest of the fleet in order to engage Taffy1. Soon after, to many's surprise, came the order to withdraw issued by Admiral Kurita. Admiral Jun Minasoko, commanding the Kokoan squadron from the Mikawa, repeatedly radioed Kurita urging him to recall the retreat and attack Taffy1 before turning against the Transports and beacheads at Leyte. Under pressure, Kurita changed course again towards the soutwest after the Japanese and Kokoan fleets had regrouped but then changed his mind again sending the Center force on a northern course once again. Minasoko kept radioing Kurita from Mikawa but to no avail. The Japanese Admiral hesitated once more but ultimatedly forced his aouthority reaffirming his orders of having the whole fleet steam back towards San Bernardino Strait.
As morale on board the Kokoan ships reached an all-time low after an almost secured victory had slipped from grasp Suruga rejoined the fleet. The battleship crew had managed to extinguish the fires and brought back in operation both forward main guns and the inboard starboard propeller.
Shortly after midnight, on October 26th, the retrating Kokoan/Japanese fleet was intercepted by Admiral Lee's formation, strong of nine Battleship (seven american, two Recerchean) and two Battlecruisers he almost achieved surpise on the battered and low on morale retrating fleet. At night, radar-guided gunfire was the deciding factor, despite beign actually outnumbered (and outgunned) Lee ships reduced Musashi, Mutsu and Nagashiro into sinking condition, also inflicting heavy damage on Kii, before the Kokoan or Japanese managed to land enough shots on target with thieir own fire-control radars. Yamato, at the front of the column was in a disadvantageous position to fire effectively, she eengaged the two Recerchean battleships Resolute and Dauntless, damaging the latter with a few lucky shots. Kongo and Haruna fired blindly at the attacking ships without achieving significant hits. The already Damaged Owari, which had suffered a torpedo hit during the Battle off Samar, turned hard to port and managed to avoid most of the incoming fire. Mikawa and Omi came under fire from the battleships Washington, Alabama and Massachussets, suffering eight and three hits respectively before returning fire, heavily damaging Alabama, while Amagi and Nagato concentrated fire on the battlecruiser USS United states, ultimately leading to her sinking.
Suruga, steaming in the rear-half of the Kokoan/Japanese column, was hit by a torpedo fired by one of the American Destroyers, The hit immediately severed the outboard starboard propeller, although the shaft was luckily left intact. However, the hit forced the Suruga to reduce speed, and the ship soon came under fire from three Iowa class battleships: Missouri, New Jersey and Iowa herself. Under the rain of 406mm (16-inch) shells the Kokoan battleship suffered multiple hits on her rear quarters. The aircraft catapult was destroyed along with one of the seaplanes and both aft turrets were put out of action. Further hits damaged the engine and boiler rooms, toppled the mainmast, punctured two fuel tanks and disabled bot aft 152mm guns and one of the 127mm anti-air mounts. Fires started again at the stern and at miship. Against all odds, after an hour of punding and beign forced to cut her speed in half at just 15 knots, Suruga manged to disengage from the enemy Battleship with what was left of the Cener Force. Most of the ships had been seriously damaged and unfit for further action, but Suruga was in a much worse shape. Pushing her battered engines to the brim, the battleship made between 15 and 20 knots for the next day, escorted by four destroyers and targeted by further air raids. Suruga engines finally broke down 10 miles off Manila, forcing tugs to tow the battleship into the harbor.
Before departing for Koko with the rest of the fleet, Admiral Minasoko personally assessed the damage on Suruga: The aircraft facilities had ben all but destroyed, with both the hangar, crane and catapult unusable, of the ariwing, only one F1M had survived, in damaged state. Three of the four secondary 152mm turrets were temporarily out of action, as it was for one of the 127mm mouns, damage was done to many of the 25mm guns too. Both aft main guns were unusable, with turret 3 beign completely wrecked, jammed in her place with the guns locked at 18° of elevation. The mainmast had collapsed to port damaging one of the HA-directors, two 25mm machine gun mounts and the roof of the aft port 152mm gun. Thirteen compartments below the waterline had suffered hits and were flooded. Boiler rooms No.3, 5, 8, 9, 11 and 12 were damaged beyond repair, as it was for engine room No.3. More, all other three engine rooms and boiler rooms No. 6, 7 and 10 needed extensive repairs to be safely used again and the outboard starboard propeller was missing. It was clear that there was no possibility for the Battleship to depart the Philippines with the rest of Koko no Kaigun warships.
With no other choice available, Suruga was berthed off Manila waterfront to be turned into an anti-air floating battery. With the few facilities available, the mangled remains of the mainmast were removed, as they were the damaged barrels of turret 3. Aircraft faclities and boats were also removed. Then wooden platforms were added above turret 4 and the former boat deck to allow for more anti-aircraft guns to be added. The 25mm anti-air suite was thus increased by removing weapons from damaged and departing ships to reach 58 triple and 48 single mounts, for a total of 222 barrels. The ship then had it's two main-gun directors pained white and a brow-green camouflage added above the former blue-black one. During the works, on October 29th Suruga came under attack from Task Force 38 planes, but the damage recieved was light, espacially if compared to the enormous punishment she had sustained during the Leyte gulf operations.
On November 6th, when koko uprisings started, Suruga was harmlessly requisitioned by the Japanese. The largest Koko no Kaigun ship to fall under IJN control, despite beign of little to no use in her state.
As soon as the Battle of Luzon began, with the Lingayen gulf landing on January 9th 1946, Suruga became the target of repeated US bombings, as the Battleship was immetiatedly recognized as a prime objective to be dealt with. A second raid was made on January 14th and a third on the 30th. More raids followed on February 3rd, 9th and 22nd. Suruga's crew ultimately surrenderd to US forces on February 25th, 1946. At that point, the battleship was nothing short of a floating wreck, with basically all of her sistems destroyed or unusable. Amazingly still, the Battleship had not sunk, despite her reserve buoancy was now at it's limits given the damage inflicted to her underwater hull by all the near-misses she suffered. Formally returned to Koko no Kaigun after the March 1946 armistice, Suruga was immediately decommissioned and her ownerships transferred to the United States Navy. After Provisional repairs had been made the Battleship was towed to the nearby port of Manila and scrapped between 1947 and 1949.
Omi and Mikawa had safely departed Manila on October 28th 1945, steaming directly for Koko and reaching Toumachi bay on november 5th. Here the ship were supposed to be further refitted, replacing the entire 25mm anti-air suite with never 40mm Type5 guns but the start of Koko uprising halted the plan. Both battleship recieved two Aichi E16A as reconnaissance units. As almost the entire Koko no Kaigun defected en-masse under Admiral Karasawa command, joining the rebel front, Mikawa kept acting as the Fleet Flagship until the armistice with the United States was signed in March 1946. By that time, the anti-air upgrade had been partially executed, with the single 25mm machine gun removed and the triple open mounts replaced by twin 40mm ones. For a mixed anti-air suite of 102 25mm and 36 40mm guns. After the armistice, both Omi and mikawa were painded ins tandard USN Measure22 camouflage, with the kokoan flag and name painted on their side. However, the Americans were reluctant to allow the two battleships to join the co-belligerent fleet, so the Flag was moved to Amagi and Mikawa was used as a floating headquarter in Toumachi Bay until the end of the war, in Semptember 1946. Omi instead sailed to Midway, where she was interned until the end of the hostilities.
Both ships were decommissioned in May 1947 under peace treaty provisions when Koko no Kaigun was reorganized into Koko Kaijou. Berthed at Teshigawa, Tenji Island, the ships sat for a little over three years awaiting disposal.
Then on, june 25th 1950, the Korean war broke out. Under joint approval given by both the United states and Kokoan governments, Omi and Mikawa returned to Toumachi in August of the same year to be refitted and brought back in service, destined to enforce naval blockade and shore bombardment of military targets in North Korea. During the refit, all the former 25mm machine guns were removed, with ten enclosed mounts modified to fit twin 40mm Type5 guns. Six quadruple mounts were also fitted, four of them replacing searchlight platforms, for a total light anti-air suite of 44 guns. All portholes in the hull were closed and the ships repainted to standard grey. Boat complement was revised and USN elecrtonics fitted, with the mainmast modified to fit an SPS-4 surface and 2D air search radar and an SX 3D air search radar. Aircraft facilities a the stern were removed to make space for an helicopter landing spot. The ships could operate two Sikorsky H-19 Chickasaw, with the former seaplane hangar accordingly modified to allow one to be stored below deck for when the main guns had to be fired. Sea trails proved that except from some interference to the bridge antennas, the high position of the radars ond other shipboard electronics kept them safe from blast pressure from the main guns. Mikawa was recommissioned on December 18th 1950, with Omi following on March 10th 1951. The two warships joined USN and JMDF ships bombarding military positions and strategic targets in North korea for the rest of the conflict.
After the war Omi recieved to newer Sikorsky H-34 helicopters and was based at Yamasaki Naval Base, Toumachi Bay, serving mainly as a training ship until October 30th 1959, when she was decommissioned for a final time. She was left in the reserve fleet to be cannibalized for spares for her sister before being eventually scrapped in 1971.
After the end of the Korean War, Mikawa was refitted again, she landed all her remaining 40mm guns and their relative fire-control equipment. The single boat crane at midship was also removed and replaced by two smallerones fitted on both sides of the aft superstructure, this allowed for a lattice mast to be erected in it's place. Shipboard electronics were upgraded again with the fitting of new long-range comunciation systems and a new radar suite, composed by an SPS-10 surface radar, and SPS-12 medium-range 2D air radar and SPS-39 medium-range 3D air radar. An UNREP station was fitted at midship and forty-eight life rafts with a total capacity carried over the standard boat complement. With a newer complement of 1.914 officers and men Mikawa became the Flagship of the northern fleet and was based at Hokuto, Tenji Island. Here she mainly operated as a fleet in beign against the Sovied Battlecruiser Kronstadt, based at Vladivostok, and it's flotilla of Sverdlovs.
In late 1961 Mikawa recieved two Sikorsky SH-3 Sea King helicopters to replace her older H-34 ones. Since the SH-3 cold not fit into the Battleship hangar both had to be stored on deck even when the main gun fired, so it was recomended to not fire directly towards the stern unless it was stricty necessary. The hangar itself was modified to act as a maintenace station for the helicopters, with all the unused space converted into living quarters for the crew. By early 1965, after growing tensions in southeast Asia had led to a large buildup of US involvement in vietnam, Koko's government started to contemplate the possibility to support American operation in the area. Since public opionion appeared more concerned about the Soviet Union threat land-based intervention was ruled out, this left a small Navy involvement to be doable. After a few meetings with US delegations it was agreed to send a small Kokoan task force to provide gunfire support to US operation. Escorted by two guided-missile Destroyers and the Aircraft Carrier Inuwashi, which were to give the ship protection from air attacks, Mikawa departed for Vietnam, reaching her planned area of operation on November 2nd 1965. Repeatedly bombarding military positions, infrastructures and supply routes, Mikawa was left stationed, in the South China Sea until September 25th 1968, when she was relieved by the Battleship USS New Jersey.
Upon her return to Koko, on October 18th, Mikawa was decommissioned again in anticipation of a possible refit to turn her into a guided missile Battleship. However concerns about operation and refit costs, budget cuts and other pratical reasons let to the plan beign shelved. At the time Miwawa was the last 460mm (18inch) gunned battleship still in service in the world. The other battlship currently in service with Koko Kaijou, the sagami, had 406mm (16-inch) guns, sharing ammunition with all the 16-inch gunned battleship still in service with the US Navy. In light of this, the Kokoan goverment preferred to follow different paths, eventually negotiation with the US Navy for the transfer of the Battleship Kentucky, which was undergoing the BBG conversion and wold soon be classified as surplus under Nixon's Vietnamization.
Under this provisions, Mikawa was stuck from the Navy list on June 1st 1969. Despite some of her former crew proposed to preserve her as a museum there was no widespread popular sentiment toward her as it was for Amagi, so eventually the massive battleships entered the yards for scrappping in 1973. Still, some relics of her were spared: one of her propellers and the main gun rangefinder set can be seen at the Yamasaki Naval Museum, outside Koko Kaijou Naval academy, Yamasaki, Koko Island.
Ships in class: (laid down-launched-commissioned - fate)
Yashima 1936-1938-1939 – Sunk 1944
Suruga 1938-1940-1941 – Joined the IJN 1945, Returned to Koko 1946, Decommissioned 1946, Ceded to the USN, 1946, Scrapped 1947
Omi 1937-1939-1941 – Decommissioned 1947, Recommissioned 1951, Decommissioned 1959, Scrapped 1971
Mikawa 1939-1942-1943 – Decommissioned 1947, Recommissioned 1950, Decommissioned 1968, scrapped 1973