IJN Kongo Design - Battlecruiser
The original design of the Kongo-class reflected the battlecruiser philosophy at its zenith, embodying Sir George Thurston's interpretation of the fast capital ship concept that had revolutionized naval thinking in the previous decade. When Kongo was laid down in 1911, she represented the cutting edge of British naval architecture adapted for Japanese requirements. The ships measured 704 feet in length with a beam of 92 feet and displaced approximately 27,500 tons at standard load. This relatively narrow beam-to-length ratio was characteristic of high-speed designs, allowing the hull to slice through water efficiently while maintaining the structural integrity needed to mount heavy armament.
The original armament scheme centered on eight BL 14-inch Mk I guns mounted in four twin turrets, arranged in the classic superfiring configuration with two forward and two aft. These weapons could hurl a 1,400-pound shell over 38,000 yards, though effective engagement ranges in the 1910s were considerably shorter. The secondary battery consisted of sixteen 6-inch guns in casemate mountings along the hull sides, intended for use against destroyers and lighter craft. Anti-torpedo boat defense was provided by eight 3-inch guns, while four submerged 21-inch torpedo tubes gave the ships an offensive weapon for close-range engagements. The fire control system, while advanced for its time, relied on optical rangefinders and mechanical computers housed in armored positions high in the superstructure.
The armor protection scheme revealed the battlecruiser's fundamental compromise. The main belt armor measured only 8 inches at its thickest point, tapering to 3 inches at the ends, compared to contemporary battleships which typically carried 12 inches or more. The deck armor was similarly modest at 2.75 inches maximum thickness. The turret faces received 9 inches of protection, while the barbettes were armored to 10 inches. This arrangement could theoretically protect against cruiser-caliber weapons and shell fragments, but would struggle against the heavy shells from enemy battleships. The conning tower, where the captain and key personnel would direct the ship in battle, received the heaviest protection at 10 inches. This armor scheme saved approximately 2,000 tons compared to a fully-protected battleship, weight that went into the propulsion system.
The original powerplant consisted of 36 Yarrow mixed-firing boilers feeding two sets of Brown-Curtis turbines, generating 64,000 shaft horsepower. This impressive machinery drove four propeller shafts and could push the ships to 27.5 knots, making them faster than any battleship afloat when completed. The coal bunkers held 2,500 tons with an additional 1,000 tons of fuel oil for supplementary firing, giving a theoretical range of 8,000 nautical miles at cruising speed. The boiler rooms and engine spaces occupied a significant portion of the hull, arranged in alternating compartments to enhance survivability if damaged.
The redesign of Kongo and her sisters stemmed from a confluence of technological evolution, tactical lessons, changing strategic requirements, and the constraints imposed by international naval treaties. Understanding why these ships underwent such radical transformation requires examining the broader context of naval development in the two decades following World War I.
The most immediate impetus came from the sobering lessons of the Battle of Jutland in 1916, which shattered many assumptions about battlecruiser design. During that engagement, three British battlecruisers—Indefatigable, Queen Mary, and Invincible—exploded catastrophically after relatively few hits from German heavy shells. These losses exposed the fatal flaw in the battlecruiser concept: insufficient armor protection made these ships vulnerable to the very weapons they themselves carried. The flash from shell hits penetrated into magazines through inadequate protection around turrets and hoists, causing explosions that destroyed the ships in minutes. Though the Kongo-class had marginally better protection than the lost British ships, Japanese naval planners recognized their vessels shared the same fundamental vulnerability. The battle demonstrated that speed could not reliably substitute for armor when engaging enemy capital ships, particularly as fire control systems improved and allowed accurate shooting at ranges where neither speed nor maneuver could prevent hits.
The Washington Naval Treaty of 1922 profoundly influenced Japanese thinking about the Kongo-class. This agreement, which aimed to prevent a ruinous naval arms race, placed strict limits on the total tonnage of capital ships each signatory nation could maintain. Japan was restricted to a ratio of 3:5 compared to Britain and the United States, meaning for every five capital ships the Anglo-American powers possessed, Japan could field only three. This numerical inferiority created an immediate strategic problem. Japanese naval doctrine anticipated a decisive battle in the western Pacific against the American fleet, and in such an engagement, quality would need to compensate for quantity. Rather than scrapping older vessels to make room for new construction, Japanese planners realized they could modernize existing ships within the treaty framework, which permitted extensive reconstruction that didn't increase displacement by more than 3,000 tons—a limit Japan eventually exceeded but initially used as justification.
Technological advances in the 1920s made reconstruction increasingly attractive compared to building new ships. Propulsion technology had evolved dramatically, with oil-fired boilers operating at higher pressures and temperatures offering far greater efficiency than the coal-fired systems of the 1910s. Turbine design had similarly improved, generating more power from smaller, lighter machinery. This meant the Japanese could remove the old powerplant, install modern equipment that occupied less space and weighed less, and use the weight savings to add armor protection. The mathematics were compelling: scrapping 36 old boilers and their associated coal bunkers freed up enormous internal volume and thousands of tons of weight that could be redistributed to armor, fuel capacity, and modern systems while actually increasing speed.
The evolution of naval warfare itself demanded faster battleships. During World War I, the battlecruiser's speed advantage proved valuable for scouting, pursuit, and operations requiring strategic mobility. By the 1920s, aircraft carriers were emerging as capital ships in their own right, and these vessels operated at speeds around 30 knots. A battle fleet built around slow battleships capable of only 21-23 knots could not effectively screen carriers or exploit the reconnaissance and striking power they provided. The Japanese Navy, which was among the most innovative in developing carrier doctrine, recognized that future naval operations would require battleships capable of keeping pace with carrier task forces. The Kongo-class, with their heritage as fast ships, presented the perfect candidates for reconstruction into high-speed battleships that could fulfill this role.
Strategic geography also shaped the decision. Japan's potential adversaries lay across vast ocean distances, and any future conflict would involve operations spanning thousands of miles. The original Kongo-class, despite their theoretical 8,000-mile range, suffered from the inefficiency of coal firing and the practical difficulties of coaling at sea or in forward anchorages. Converting entirely to oil firing with modern, efficient machinery increased operational range while making underway refueling practical. The ships' high speed, combined with extended range, would allow them to respond rapidly to threats across Japan's expansive defensive perimeter, raid enemy commerce routes, or pursue retreating forces—capabilities that slow battleships simply could not provide.
The rise of naval aviation created both threats and opportunities that influenced the reconstruction plans. By the 1930s, it was clear that aircraft carriers would play a major role in future naval warfare, and battleships needed enhanced anti-aircraft capabilities. The original Kongo-class had virtually no effective defense against air attack. The reconstructions incorporated substantial anti-aircraft batteries and modern fire control systems designed specifically for engaging aircraft. More fundamentally, the massive pagoda superstructures built during reconstruction reflected Japanese thinking about combat direction. These towering structures provided elevated positions for observers and fire control directors, essential for coordinating air defenses and directing the ship's main battery against surface targets at the extended ranges that modern fire control made possible.
Economic considerations played a surprisingly significant role. Building new battleships was extraordinarily expensive, requiring years of construction and consuming vast quantities of strategic materials like armor plate and heavy forgings. Japan's industrial capacity, while impressive, could not match that of the United States or Britain. Reconstructing existing hulls offered a way to achieve near-modern capabilities at roughly half the cost and time of new construction. The basic hull structure, while requiring reinforcement and modification, remained sound. The armor belt, though inadequate by modern standards, could be supplemented rather than completely replaced. Most importantly, the major caliber guns and turrets—representing enormous investments in precision engineering—could be retained, refurbished, and updated rather than scrapped. This economic logic became even more compelling during the Great Depression, when naval budgets faced scrutiny and the efficient use of existing assets became paramount.
The international political climate of the 1930s provided additional urgency. Japan's withdrawal from the League of Nations in 1933 following the Manchurian Incident, and subsequent abandonment of naval treaty limitations in 1936, created an atmosphere where military expansion seemed both necessary and possible. The reconstruction of the Kongo-class accelerated during this period, driven by nationalistic fervor and the perception that war with Western powers was increasingly likely. Improving these ships became not merely a naval technical matter but part of a broader program of military modernization intended to establish Japanese dominance in East Asia.
Finally, there was an element of pride and prestige involved. Kongo herself, having been built in Britain, represented both a connection to and competition with the Royal Navy. Demonstrating that Japanese engineering could transform a British design into something superior appealed to national sentiment. The other three ships, built in Japan to British plans, could similarly be improved beyond their original specifications, proving Japanese technical competence. The reconstructed Kongo-class became showcases for Japanese naval architecture and engineering prowess, their distinctive pagoda superstructures creating an instantly recognizable Japanese aesthetic that differentiated them from Western designs.
The decision to reconstruct rather than replace the Kongo-class ultimately reflected pragmatic calculation. These ships occupied a unique niche—too valuable to scrap, too outdated to use without modification, yet possessing fundamental characteristics that made them worth preserving. Their size, speed potential, and existing armament provided a foundation upon which modern capabilities could be built. The alternative—building four entirely new fast battleships—would have consumed resources Japan needed for other construction, including the massive Yamato-class super-battleships that were already straining Japanese shipbuilding capacity. By reconstructing the Kongo-class, Japan created four capable fast battleships that could screen carriers, pursue enemy forces, and fight in the battle line, all while conserving resources and maintaining the numerical strength of the battle fleet within treaty limitations, at least initially. The extensive nature of these reconstructions—essentially rebuilding everything above the waterline and most of the internal spaces—testified to how thoroughly the original battlecruiser concept had become obsolete, and how completely Japanese naval thinking had evolved in the interwar period.
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