The North PacificBoard

Preliminary studies for a new class of battleships began from 2015 to 2019, 13 initial designs were put forth, 6 of them being the Seiran class concepts. The Nareba-Hokkaku Shipyard concept varied greatly in armament, propulsion, endurance, and armor. Main batteries fluctuated between 410 mm (16.1 in) and 480 mm (18.9 in) guns, while the secondary armaments were composed of differing numbers of 130 mm (5.1 in), 127 mm (5 in), and 25 mm (1 in) guns. Propulsion in most of the designs was a hybrid diesel-turbine combination, though one relied solely on nuclear reactors and another planned for Combined Propulsion, The maximum range of the various designs was between 20,000 nmi (37,040 km; 23,015 mi) in design to a high of 33,400 nmi (61,856 km; 38436 mi). Armor varied between providing protection from the fire of high caliber guided precision guns to enough protection against Anti-Ship Missiles.

After these had been reviewed, one of the original six were finalized. The final design called for a standard displacement of 82,310 long tons (92,187 t) (planned), making the ships of the class the largest battleships yet designed. The design called for a main armament of nine 480 mm naval guns, mounted in three triple-gun turrets—each of which weighed more than a destroyer. Due to the unlimited weight designation made by the navy, Superior armor of the warship was achieved through thickening some armor elements and substituting construction steel with armor-grade Special Treatment Steel (STS) in certain areas.

However, introducing a 480mm gun that hasn't been used once except during the Ryuna Island Crisis, have been an issue for the designers to fit the gun on an existing, pre-1940's turret, thus lengthening the final design phase of the battleship until 2021, the design branch continued working on the turret with a larger barbette. As these branches were dependent on one another, they were not able to finalize the design due to the size of the turret, which also forced them to enlarge the hull to balance buoyancy of the battleship. When the contract design was in the final stages of refinement, the ships could not use the larger barbette, as it would require extensive alterations to the design and would result in substantial error in statistics. A complete scrapping of plans was avoided only when designers within the Bureau of Ordnance were able to design a new 62-caliber gun, the Type-20, that was larger to fit the triple gun in outside diameter; this allowed it to be placed in a turret that would fit in the smaller barbette. The redesigned 3-gun turret, equipped as it was with the Type-20 naval gun, is able to operate normally without any issues.

As 2021 drew to a close the contract design of the Seiran was nearly complete, but it would continuously evolve as the Nareba-Hokkaku Shipyard conducted the final detail design. These revisions included changing the design of the superstructure to fit the Aegis Combat System and updated Cooperative Engagement Capability System, adding Type-15 Kairyū Guided Missile Launching System on top of the armored lower bridge and two amidships, and moving the combat information center into the armored superstructure. Additionally, the internal subdivision of the machinery rooms were greatly modified, as tests had shown the underwater protection in these rooms to be inadequate. The longitudinal subdivision of these rooms was doubled, and the result of this was clearly beneficial: "The prospective effect of flooding was roughly halved and the number of uptakes and hence of openings in the third deck greatly reduced." Although the changes meant extra weight, this was no longer a major issue. There is also considerable increase in anti-aircraft armament along with their associated splinter protection and crew accommodations, and additional electronics.

General Characteristics

The Seiran-class battleships are designed to have good stability and control, thanks to the installation of enhanced gun laying drives and vertical stabilizers. These features contribute to making the Seiran-class battleships steady gun platforms, ensuring accurate and effective gunfire. However, due to their size, they are somewhat sluggish in terms of maneuverability in open waters. Although the Seiran-class battleships exhibit good seakeeping capabilities, they are not considered outstanding in this regard. The hull design, characterized by a long fine bow and a sudden widening of the hull just in front of the foremost turret, contributes to the ships being relatively wet for their size. This hull form, shared with the Fujiwara-class ships, results in the formation of intense sprays during operations, which can pose challenges during refueling operations with escorting destroyers. One notable feature of the Seiran-class battleships is the presence of overhead rails on the ship's broadway. The broadway refers to the wide passageway that runs down the middle of the ship, connecting all three turrets. The overhead rails are utilized to facilitate the movement of shells between the ship's three main gun magazines. For example, they allow the aft turrets to supply additional shells to the forward turrets, helping to balance the ammunition supplies and ensure a continuous rate of fire during combat situations.

Propulsors

The Seiran-class battleships of the Fujiwara National Naval Corps introduced a remarkable departure from conventional warship propulsion systems by adopting contra-rotating propulsors, an innovative marine propulsion configuration primarily utilized by smaller vessels. These cutting-edge propellers, rotating in opposite directions, revolutionized the battleships' performance and efficiency, thus distinguishing them from their counterparts relying on traditional bladed propellers.

The utilization of contra-rotating propulsors endows the Seiran-class battleships with several noteworthy advantages. One key benefit lies in the substantial reduction of power output required to achieve high velocities. The counter-rotating propellers facilitate the generation of an augmented propulsive force, enabling the battleships to navigate through water with superior efficiency. Consequently, this heightened efficiency translates into reduced fuel consumption, optimizing overall operational effectiveness. The Seiran-class battleships, propelled by contra-rotating propulsors, exhibit the remarkable capability to sustain high speeds while maximizing fuel efficiency, thereby extending their operational range and endurance.

Notably, the implementation of contra-rotating propulsors enhances the battleships' maneuverability and control. The opposing flow of water engendered by the propellers bolsters the vessels' responsiveness to steering commands, facilitating swift alterations in direction and precise maneuvering across diverse operational scenarios. This maneuverability advantage proves particularly advantageous during naval engagements, equipping the battleships with the agility to expeditiously adapt their position and effectively respond to evolving tactical exigencies.

Beyond their functional merits, contra-rotating propulsors confer supplementary advantages, such as diminished noise and vibration levels compared to traditional propeller systems. The resultant reduction in acoustic and mechanical disturbances augments both acoustic stealth, thereby enhancing the battleships' covert operations, and the well-being of the onboard personnel by minimizing disruptive vibrations.

Armaments

The Seiran-class battleships had primary armaments of nine 48 cm/62 caliber Type 20 naval guns weighing 2,730.2 tons (2,774 mt) – one of the largest guns ever fitted to a warship – The guns are housed in three 3-gun turrets: two forward of the battleship's superstructure and one aft, which could fire 1,460 kg (3,220 lb) armor-piercing shells at a muzzle velocity of 780 m/s (2,559 ft/s) and 1,410 kg (3,108 lbs) high explosive shell at a muzzle velocity of 805 m/s (2,641 ft/s) out to 42.0 km (26.1 mi) at a rate of 1.8 to 2.5 shells per minute. The turrets are "three-gun", not "triple", because each barrel is individually sleeved and can be elevated and fired independently.

The Seiran-class battleships are equipped with powerful main guns that have the capability to fire 1,360 kg (3,000 lb) Fuel Air Incendiary Shells. These shells are designed to cause devastating damage upon detonation. The shells are equipped with a time fuze, which allows the crew to set the distance at which they will explode. When the shells detonate, the first explosive charge ruptures the container at a predetermined height. This releases the fuel contained within the shell, creating a cloud that mixes with the surrounding atmospheric oxygen. The fuel-air mixture produced by the detonation flows around objects and penetrates structures. This creates a highly volatile situation. The second explosive charge is then triggered, causing the cloud of fuel and oxygen to detonate. The resulting blast wave is extremely powerful, burning at temperatures as high as 3,000 °C (5,430 °F) and generating a flame that spans approximately 5 meters (16 feet) in width. The destructive capability of these shells is immense. The blast wave can demolish reinforced buildings, destroy equipment, and cause significant harm to individuals in the vicinity. While these shells are not suitable for ship-to-ship combat, high-altitude engagements, or adverse weather conditions due to their reliance on atmospheric oxygen, they prove to be highly effective against field fortifications such as foxholes, tunnels, bunkers, and caves. The use of Fuel Air Incendiary Shells by the Seiran-class battleships adds a formidable tool to their arsenal, enabling them to neutralize and destroy enemy fortifications with great efficiency.

Although not primarily used, Seiran has a reserve of 20 naval artillery cluster munitions shells designed to detonate after penetrating an enemy ship and served as a specialized ammunition used in naval warfare. This type of shell is specifically engineered to cause devastating damage to enemy vessels by releasing a cluster of submunitions inside the target ship. The shell itself is larger and heavier than standard projectiles, allowing it to carry a significant payload of submunitions. It is designed with a reinforced casing to withstand the forces encountered during firing and penetration. Upon impact with the enemy ship's hull, the shell is engineered to penetrate the outer layers and reach the interior compartments. It is equipped with a delayed detonation mechanism that activates after a predetermined period or upon reaching a specific location within the ship. Once the shell reaches its intended location, it releases a cluster of submunitions designed to cause maximum destruction within the vessel. These submunitions can vary in nature and purpose, such as high-explosive charges, incendiary devices, or anti-personnel fragments. The submunitions disperse throughout the target ship, utilizing their individual explosive capabilities to inflict widespread damage. They can breach bulkheads, rupture compartments, and ignite fires, leading to catastrophic consequences for the enemy vessel. The delayed detonation of the shell allows it to penetrate deeply into the ship before unleashing its destructive payload. This ensures that critical areas, such as engine rooms, ammunition stores, or command centers, are effectively targeted, crippling the ship's functionality and reducing its combat effectiveness. The utilization of naval artillery cluster munitions shells that detonate after penetrating enemy ships provides a potent capability for naval forces. By specifically targeting vital areas within the vessel, these shells aim to incapacitate or sink enemy ships, disrupting their operations and giving a significant advantage to friendly forces.

Armor

The Seiran-class battleships were meticulously designed to engage multiple enemy battleships simultaneously and possess exceptional defensive capabilities against various surface threats. These warships were equipped with heavy armor plating that provided an unprecedented level of protection in surface combat. The Seiran were fitted with heavy armor plating described as an unparalleled degree of protection in surface combat. The main belt of armor along the side of the vessel was up to 430 mm (17 in) thick, The transverse bulkheads of the armored citadel, which housed vital components, boasted a thickness of up to 380 mm (15 inches). In addition, a lower belt armor, measuring 205 mm (8.05 inches) thick, was added beneath the main belt in response to gunnery experiments conducted by the Kongō and Fujiwara-class ships. Furthermore, the top hull shape was very advanced, the peculiar sideways curving effectively maximizing armor protection and structural rigidity while optimizing buoyancy. The top hull shape of the Seiran-class battleships was an engineering marvel. Its distinctive sideways curvature maximized the effectiveness of armor protection, enhanced structural rigidity, and optimized buoyancy. Even the armor on the main turrets surpassed that of the main belt, with turret face plating reaching an astonishing thickness of 650 mm (26 inches). Both the main belt and main turret armor plates were composed of hardened homogenous steel, an alloy of two classes of steel armor, ensuring exceptional resilience. Main armored deck—200 mm (7.9 in) thick—was composed of a special treatment steel (STS), a high-tensile structural steel. Additional plating was designed by manipulating the STS outer hull plating.

The critical citadel area, encompassing the magazines and engine rooms, received additional protection with an outer hull plating made of special treatment steel (STS). Several additional extra armor were strategically positioned to defend against raking fire directly overhead. The deck armor consists of a 40 mm (1.5 inch) thick STS weather deck, a combined 152 mm (6.10 inch) thick Class B and STS main armor deck, and a 20mm (0.7 inch ) thick STS splinter deck, which was considered more likely given the possibility for enemies to penetrate the decks. Over the magazines, the splinter deck is replaced by a 25 mm (1 inch) STS third deck that separates the magazine from the main armored deck. The powder magazine rooms are separated from the turret platforms by a pair of 1.5 inch STS annular bulkheads under the barbettes for flashback protection.

To counter torpedo threats, the Seiran-class battleships employed a sophisticated multiple bulkhead side protection system. This system consisted of several void spaces and the lower belt armor, with a depth of 6.1 m (20 ft), effectively absorbing the energy of a torpedo warhead. Designed to withstand a 700 kg (1,543 lb) TNT charge, the torpedo bulkheads were engineered to elastically deform, dissipating energy. The outer compartments were liquid loaded to disrupt the gas bubble and slow down fragments. The outer hull was specifically constructed to detonate a torpedo, while the outer two liquid compartments absorbed the shock and decelerated any splinters or debris. The lower armored belt and the empty compartment behind it absorbed any remaining energy.

Preliminary studies for a new class of battleships began from 2015 to 2019, 13 initial designs were put forth, 6 of them being the Seiran class concepts. The Nareba-Hokkaku Shipyard concept varied greatly in armament, propulsion, endurance, and armor. Main batteries fluctuated between 410 mm (16.1 in) and 480 mm (18.9 in) guns, while the secondary armaments were composed of differing numbers of 130 mm (5.1 in), 127 mm (5 in), and 25 mm (1 in) guns. Propulsion in most of the designs was a hybrid diesel-turbine combination, though one relied solely on nuclear reactors and another planned for Combined Propulsion, The maximum range of the various designs was between 20,000 nmi (37,040 km; 23,015 mi) in design to a high of 33,400 nmi (61,856 km; 38436 mi). Armor varied between providing protection from the fire of high caliber guided precision guns to enough protection against Anti-Ship Missiles.

After these had been reviewed, one of the original six were finalized. The final design called for a standard displacement of 82,310 long tons (92,187 t) (planned), making the ships of the class the largest battleships yet designed. The design called for a main armament of nine 480 mm naval guns, mounted in three triple-gun turrets—each of which weighed more than a destroyer. Due to the unlimited weight designation made by the navy, Superior armor of the warship was achieved through thickening some armor elements and substituting construction steel with armor-grade Special Treatment Steel (STS) in certain areas.

However, introducing a 480mm gun that hasn't been used once except during the Ryuna Island Crisis, have been an issue for the designers to fit the gun on an existing, pre-1940's turret, thus lengthening the final design phase of the battleship until 2021, the design branch continued working on the turret with a larger barbette. As these branches were dependent on one another, they were not able to finalize the design due to the size of the turret, which also forced them to enlarge the hull to balance buoyancy of the battleship. When the contract design was in the final stages of refinement, the ships could not use the larger barbette, as it would require extensive alterations to the design and would result in substantial error in statistics. A complete scrapping of plans was avoided only when designers within the Bureau of Ordnance were able to design a new 62-caliber gun, the Type-20, that was larger to fit the triple gun in outside diameter; this allowed it to be placed in a turret that would fit in the smaller barbette. The redesigned 3-gun turret, equipped as it was with the Type-20 naval gun, is able to operate normally without any issues.

As 2021 drew to a close the contract design of the Seiran was nearly complete, but it would continuously evolve as the Nareba-Hokkaku Shipyard conducted the final detail design. These revisions included changing the design of the superstructure to fit the Aegis Combat System and updated Cooperative Engagement Capability System, adding Type-15 Kairyū Guided Missile Launching System on top of the armored lower bridge and two amidships, and moving the combat information center into the armored superstructure. Additionally, the internal subdivision of the machinery rooms were greatly modified, as tests had shown the underwater protection in these rooms to be inadequate. The longitudinal subdivision of these rooms was doubled, and the result of this was clearly beneficial: "The prospective effect of flooding was roughly halved and the number of uptakes and hence of openings in the third deck greatly reduced." Although the changes meant extra weight, this was no longer a major issue. There is also considerable increase in anti-aircraft armament along with their associated splinter protection and crew accommodations, and additional electronics.

General Characteristics

The Seiran-class battleships are designed to have good stability and control, thanks to the installation of enhanced gun laying drives and vertical stabilizers. These features contribute to making the Seiran-class battleships steady gun platforms, ensuring accurate and effective gunfire. However, due to their size, they are somewhat sluggish in terms of maneuverability in open waters. Although the Seiran-class battleships exhibit good seakeeping capabilities, they are not considered outstanding in this regard. The hull design, characterized by a long fine bow and a sudden widening of the hull just in front of the foremost turret, contributes to the ships being relatively wet for their size. This hull form, shared with the Fujiwara-class ships, results in the formation of intense sprays during operations, which can pose challenges during refueling operations with escorting destroyers. One notable feature of the Seiran-class battleships is the presence of overhead rails on the ship's broadway. The broadway refers to the wide passageway that runs down the middle of the ship, connecting all three turrets. The overhead rails are utilized to facilitate the movement of shells between the ship's three main gun magazines. For example, they allow the aft turrets to supply additional shells to the forward turrets, helping to balance the ammunition supplies and ensure a continuous rate of fire during combat situations.

Propulsors

The Seiran-class battleships of the Fujiwara National Naval Corps introduced a remarkable departure from conventional warship propulsion systems by adopting contra-rotating propulsors, an innovative marine propulsion configuration primarily utilized by smaller vessels. These cutting-edge propellers, rotating in opposite directions, revolutionized the battleships' performance and efficiency, thus distinguishing them from their counterparts relying on traditional bladed propellers.

The utilization of contra-rotating propulsors endows the Seiran-class battleships with several noteworthy advantages. One key benefit lies in the substantial reduction of power output required to achieve high velocities. The counter-rotating propellers facilitate the generation of an augmented propulsive force, enabling the battleships to navigate through water with superior efficiency. Consequently, this heightened efficiency translates into reduced fuel consumption, optimizing overall operational effectiveness. The Seiran-class battleships, propelled by contra-rotating propulsors, exhibit the remarkable capability to sustain high speeds while maximizing fuel efficiency, thereby extending their operational range and endurance.

Notably, the implementation of contra-rotating propulsors enhances the battleships' maneuverability and control. The opposing flow of water engendered by the propellers bolsters the vessels' responsiveness to steering commands, facilitating swift alterations in direction and precise maneuvering across diverse operational scenarios. This maneuverability advantage proves particularly advantageous during naval engagements, equipping the battleships with the agility to expeditiously adapt their position and effectively respond to evolving tactical exigencies.

Beyond their functional merits, contra-rotating propulsors confer supplementary advantages, such as diminished noise and vibration levels compared to traditional propeller systems. The resultant reduction in acoustic and mechanical disturbances augments both acoustic stealth, thereby enhancing the battleships' covert operations, and the well-being of the onboard personnel by minimizing disruptive vibrations.

Armaments

The Seiran-class battleships had primary armaments of nine 48 cm/62 caliber Type 20 naval guns weighing 2,730.2 tons (2,774 mt) – one of the largest guns ever fitted to a warship – The guns are housed in three 3-gun turrets: two forward of the battleship's superstructure and one aft, which could fire 1,460 kg (3,220 lb) armor-piercing shells at a muzzle velocity of 780 m/s (2,559 ft/s) and 1,410 kg (3,108 lbs) high explosive shell at a muzzle velocity of 805 m/s (2,641 ft/s) out to 42.0 km (26.1 mi) at a rate of 1.8 to 2.5 shells per minute. The turrets are "three-gun", not "triple", because each barrel is individually sleeved and can be elevated and fired independently.

The Seiran-class battleships are equipped with powerful main guns that have the capability to fire 1,360 kg (3,000 lb) Fuel Air Incendiary Shells. These shells are designed to cause devastating damage upon detonation. The shells are equipped with a time fuze, which allows the crew to set the distance at which they will explode. When the shells detonate, the first explosive charge ruptures the container at a predetermined height. This releases the fuel contained within the shell, creating a cloud that mixes with the surrounding atmospheric oxygen. The fuel-air mixture produced by the detonation flows around objects and penetrates structures. This creates a highly volatile situation. The second explosive charge is then triggered, causing the cloud of fuel and oxygen to detonate. The resulting blast wave is extremely powerful, burning at temperatures as high as 3,000 °C (5,430 °F) and generating a flame that spans approximately 5 meters (16 feet) in width. The destructive capability of these shells is immense. The blast wave can demolish reinforced buildings, destroy equipment, and cause significant harm to individuals in the vicinity. While these shells are not suitable for ship-to-ship combat, high-altitude engagements, or adverse weather conditions due to their reliance on atmospheric oxygen, they prove to be highly effective against field fortifications such as foxholes, tunnels, bunkers, and caves. The use of Fuel Air Incendiary Shells by the Seiran-class battleships adds a formidable tool to their arsenal, enabling them to neutralize and destroy enemy fortifications with great efficiency.

Although not primarily used, Seiran has a reserve of 20 naval artillery cluster munitions shells designed to detonate after penetrating an enemy ship and served as a specialized ammunition used in naval warfare. This type of shell is specifically engineered to cause devastating damage to enemy vessels by releasing a cluster of submunitions inside the target ship. The shell itself is larger and heavier than standard projectiles, allowing it to carry a significant payload of submunitions. It is designed with a reinforced casing to withstand the forces encountered during firing and penetration. Upon impact with the enemy ship's hull, the shell is engineered to penetrate the outer layers and reach the interior compartments. It is equipped with a delayed detonation mechanism that activates after a predetermined period or upon reaching a specific location within the ship. Once the shell reaches its intended location, it releases a cluster of submunitions designed to cause maximum destruction within the vessel. These submunitions can vary in nature and purpose, such as high-explosive charges, incendiary devices, or anti-personnel fragments. The submunitions disperse throughout the target ship, utilizing their individual explosive capabilities to inflict widespread damage. They can breach bulkheads, rupture compartments, and ignite fires, leading to catastrophic consequences for the enemy vessel. The delayed detonation of the shell allows it to penetrate deeply into the ship before unleashing its destructive payload. This ensures that critical areas, such as engine rooms, ammunition stores, or command centers, are effectively targeted, crippling the ship's functionality and reducing its combat effectiveness. The utilization of naval artillery cluster munitions shells that detonate after penetrating enemy ships provides a potent capability for naval forces. By specifically targeting vital areas within the vessel, these shells aim to incapacitate or sink enemy ships, disrupting their operations and giving a significant advantage to friendly forces.

Armor

The Seiran-class battleships were meticulously designed to engage multiple enemy battleships simultaneously and possess exceptional defensive capabilities against various surface threats. These warships were equipped with heavy armor plating that provided an unprecedented level of protection in surface combat. The Seiran were fitted with heavy armor plating described as an unparalleled degree of protection in surface combat. The main belt of armor along the side of the vessel was up to 430 mm (17 in) thick, The transverse bulkheads of the armored citadel, which housed vital components, boasted a thickness of up to 380 mm (15 inches). In addition, a lower belt armor, measuring 205 mm (8.05 inches) thick, was added beneath the main belt in response to gunnery experiments conducted by the Kongō and Fujiwara-class ships. Furthermore, the top hull shape was very advanced, the peculiar sideways curving effectively maximizing armor protection and structural rigidity while optimizing buoyancy. The top hull shape of the Seiran-class battleships was an engineering marvel. Its distinctive sideways curvature maximized the effectiveness of armor protection, enhanced structural rigidity, and optimized buoyancy. Even the armor on the main turrets surpassed that of the main belt, with turret face plating reaching an astonishing thickness of 650 mm (26 inches). Both the main belt and main turret armor plates were composed of hardened homogenous steel, an alloy of two classes of steel armor, ensuring exceptional resilience. Main armored deck—200 mm (7.9 in) thick—was composed of a special treatment steel (STS), a high-tensile structural steel. Additional plating was designed by manipulating the STS outer hull plating.

The critical citadel area, encompassing the magazines and engine rooms, received additional protection with an outer hull plating made of special treatment steel (STS). Several additional extra armor were strategically positioned to defend against raking fire directly overhead. The deck armor consists of a 40 mm (1.5 inch) thick STS weather deck, a combined 152 mm (6.10 inch) thick Class B and STS main armor deck, and a 20mm (0.7 inch ) thick STS splinter deck, which was considered more likely given the possibility for enemies to penetrate the decks. Over the magazines, the splinter deck is replaced by a 25 mm (1 inch) STS third deck that separates the magazine from the main armored deck. The powder magazine rooms are separated from the turret platforms by a pair of 1.5 inch STS annular bulkheads under the barbettes for flashback protection.

To counter torpedo threats, the Seiran-class battleships employed a sophisticated multiple bulkhead side protection system. This system consisted of several void spaces and the lower belt armor, with a depth of 6.1 m (20 ft), effectively absorbing the energy of a torpedo warhead. Designed to withstand a 700 kg (1,543 lb) TNT charge, the torpedo bulkheads were engineered to elastically deform, dissipating energy. The outer compartments were liquid loaded to disrupt the gas bubble and slow down fragments. The outer hull was specifically constructed to detonate a torpedo, while the outer two liquid compartments absorbed the shock and decelerated any splinters or debris. The lower armored belt and the empty compartment behind it absorbed any remaining energy.