While the Imperial Navy was expanding its fleet under the Circle 1, 2, and 3 Plans, it was also proceeding with plans to convert existing ships at the same time. The first priority was the conversion of six battleships into aircraft carriers. The Kongō-class battleships, originally built as battlecruisers, were targeted for this conversion. By upgrading their outdated engines to the latest technology, they were expected to reach a speed of 30 knots, making them suitable as aircraft carriers. Similarly, the Nagato-class battleships, which boasted an impressive speed of 26,5 knots at the time of completion, were expected to reach 29 knots with the same modifications as the Kongō-class.
However, some advocates of air power argued that retaining the battleships Nagato and Mutsu, equipped with 41 cm guns, as battleships would limit interference with the military preparedness of other nations. If Japan didn't possess battleships, there would be no need for other nations to counteract that force, thus increasing the freedom of military preparations for potential adversaries like the United States and the United Kingdom. In response to such concerns, Marshal Admiral Prince Fushimi decided to withdraw the conversion plan for the popular Nagato and Mutsu, opting instead to upgrade their engines and designate them as fast battleships.
Regarding the conversion of the four Kongō-class battleships into aircraft carriers, some suggested that building entirely new carriers might be more cost-effective. Despite their impressive speed, the Kongō-class battleships were aging vessels designed and built in the Meiji era. Investing substantial modification costs in these vessels, approaching the end of their service life, raised valid concerns.
Prince Fushimi, prioritizing the shift from battleship-centric thinking to airpower dominance, understood the reasonable arguments against the conversion. However, his primary goal was to crush battleships and diminish the influence of naval traditionalists. Consequently, the proposal for new aircraft carriers was rejected.
The converted Kongō-class carriers were expected to transform into formidable carriers, with a flight deck of 220 meters in length, a width of 34 meters, and two hangars capable of operating 54 planes. Additionally, the Nagato and Mutsu were to become fast battleships with a 70% increase in output after engine upgrades and stern extension work to reduce propulsion resistance, achieving a speed of 29 knots and significantly improving operational flexibility.
Similar to the main fleet, auxiliary vessels underwent extensive modifications. Heavy cruisers Furutaka and Aoba were equipped with new 12,7 cm twin high-angle guns, along with increased machine guns, while removing reloading mechanisms and spare torpedoes to avoid top-heaviness due to excessive armament. Cruisers of the Myōkō and Takao classes had their third turrets removed and replaced with high-angle guns and machine guns, becoming so-called anti-aircraft cruisers equipped with Type 89 12,7 cm twin high-angle guns each.
Obsolete light cruisers such as the Tenryū-class, Yūbari, and the 5.500-ton class underwent significant transformations. They removed some or all of their guns and torpedo launchers, replacing them with enhanced anti-aircraft guns, surpassing similar-class cruisers in other nations in terms of anti-air capabilities.
Destroyers Fubuki, Hatsuharu, and Shiratsuyu classes had their main guns changed from horizontal fire to high-angle guns, along with additional machine guns. In exchange, the Fubuki-class sacrificed spare torpedoes, while the Hatsuharu and Shiratsuyu classes removed them along with the reloading systems.
Older first-class and second-class destroyers, including the Mutsuki-class, underwent thorough changes. All but one torpedo launcher was removed for self-defense, replacing main guns with high-angle guns, and updating anti-submarine equipment like sonar and depth charges to modern standards.
Certainly, these modifications and refitting were not feasible in a short time, especially in Japan with limited naval facilities. Moreover, besides the primary goal of enhancing naval capabilities, secondary objectives included job security for workers and the continuity of technological expertise. Therefore, these endeavors were expected to span multiple years.
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Aviation-Centric Combined Fleet
Historical Fiction「It is no longer the era of battleships. From now on, airplanes are the mainstay of the Navy.」 Which one is it? The doctrine of big ships and big guns or perhaps air power? The power struggle within the Navy, however, takes an unexpected turn. Due t...
