IJN Kongo Class Battleship Redesign
The first reconstruction period, beginning with Hiei in 1929 and continuing through the mid-1930s for the other ships, transformed these vessels almost beyond recognition. The hull was lengthened by 26 feet to 728 feet overall, improving seakeeping and allowing for the installation of anti-torpedo bulges along the waterline. These bulges added significant beam, increasing it to 95 feet, and provided crucial protection against underwater weapons. The displacement swelled to over 31,000 tons standard, reflecting the massive additions of armor and equipment. The bow was reshaped with more flare and increased freeboard, addressing problems with wetness in heavy seas that had plagued the original design.
The armor transformation was extensive and addressed the most critical vulnerability of the battlecruiser design. The main belt was increased to 10 inches over the machinery spaces, with an additional external plate added in some areas. More importantly, the horizontal protection received dramatic enhancement as naval warfare had demonstrated that long-range plunging fire posed the greatest threat. The deck armor was rebuilt in multiple layers, creating a complex system with a total thickness approaching 4 to 5 inches in critical areas. The magazines, ammunition handling rooms, and machinery spaces received special attention, with additional splinter protection and improved subdivision of compartments. The turret armor was also enhanced, and improved internal arrangements reduced the risk of flash fires reaching the magazines.
The propulsion system underwent complete replacement, representing perhaps the most radical aspect of the reconstruction. The 36 mixed-firing boilers were scrapped in favor of just 8 modern Kampon oil-fired boilers operating at much higher pressures. These fed into new turbines generating 136,000 shaft horsepower, more than double the original output. The efficiency improvements were staggering—fewer boilers producing more power meant reduced crew requirements, less maintenance, and improved reliability. The adoption of oil firing exclusively eliminated the backbreaking labor of coaling ship and increased operational range to approximately 10,000 nautical miles. Most impressively, despite the massive increase in displacement, the ships could now achieve 30 knots, actually faster than their original design speed.
The superstructure transformation created the distinctive appearance for which the Kongo-class became famous. The original tripod masts gave way to massive pagoda-style structures that rose in diminishing tiers, each level housing different functions. The foremast contained the main fire control directors, observation posts, searchlight platforms, and range-finding equipment, creating a tower that reached nearly 100 feet above the waterline. This vertical arrangement reflected the Japanese Navy's emphasis on visual spotting and optical fire control, placing observers as high as possible for maximum visual range. The weight and complexity of these structures presented engineering challenges, requiring careful attention to top-weight and stability, but they gave the ships a commanding, fortress-like appearance that became iconic.
The armament evolved significantly during these reconstructions, though the main battery remained the original 14-inch guns—now re-bored and re-lined to extend their service life and updated with improved fire control. The secondary battery underwent complete revision, with the vulnerable casemate-mounted 6-inch guns removed and replaced by fourteen 6-inch guns in seven twin turrets, providing all-weather capability and much better protection for the gun crews. The anti-aircraft battery received continuous attention throughout the 1930s and into the war years, eventually mounting anywhere from eight to twelve 5-inch dual-purpose guns in twin mounts, supplemented by numerous 25mm automatic weapons. By 1944, the survivors bristled with over 100 light anti-aircraft guns as the aerial threat grew overwhelming.
The fire control and sensors represented another quantum leap forward. The reconstructed ships received Type 94 fire control directors with coincidence rangefinders measuring up to 10 meters in length, among the finest optical instruments in any navy. Mechanical fire control computers continuously improved in sophistication, calculating solutions that accounted for target motion, own-ship motion, wind, temperature, and projectile characteristics. During World War II, radar was progressively added—first search radar, then fire control radar, though Japanese radar technology generally lagged behind Western developments. The ships also received improved communications equipment, plotting rooms, and damage control systems that reflected hard-won lessons from earlier naval battles.
The internal arrangements underwent equally dramatic changes during reconstruction. The crew accommodations were modernized, though they remained Spartan by Western standards. The command spaces were enlarged and better protected. The magazines were reconfigured for improved shell and powder handling, with enhanced safety features to prevent the catastrophic explosions that had doomed several battlecruisers at Jutland. The engineering spaces were reorganized around the new, more compact machinery, creating additional storage and improved damage control access. Fuel tankage was redistributed throughout the hull, providing both greater capacity and improved underwater protection, as liquid-filled spaces could absorb torpedo hits better than empty ones.
By the time these reconstructions were complete in the late 1930s, the Kongo-class bore little resemblance to the ships that had entered service twenty-five years earlier. They had been transformed from lightly-armored battlecruisers into genuine fast battleships, capable of standing in the line of battle while maintaining the speed necessary to operate with carrier forces. The displacement had grown to over 36,000 tons at full load, the crew complement had increased from about 1,200 to over 1,400 men, and every system had been modernized. Yet they retained the fundamental hull form and turret arrangement of their original design, a testament to the soundness of Thurston's basic architecture and the skill of Japanese naval engineers in adaptation and improvement.
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