The Circle 2 Plan, like the Circle 1 Plan heavily influenced by Marshal Admiral Prince Fushimi's intentions, aimed to strengthen aviation preparedness to the maximum extent within the limits of not violating arms reduction treaties. Firstly, in line with the Circle 1 Plan, four aircraft carriers were to be constructed to play a decisive role in naval aviation warfare. During the London Naval Conference, the Imperial Navy secured a carrier allocation of 135.000 tons, 10% of the United States and the United Kingdom combined. After considering the type of ships to be built, a decision was made to adopt medium-sized carriers that could align with the trend of large and high-speed carrier-based aircraft while ensuring the greatest possible number within the allocated tonnage.
Initially, names such as Sōryū and Shōkaku, featuring auspicious flying animals, were strong contenders for the carriers. However, considering Prince Fushimi's opinion that carriers are the capital ships and should bear old province names or mountain names, it was decided that large carriers would carry old province names, while medium and small carriers would bear mountain names.
Regarding auxiliary vessels, 14 units of the heavily torpedo-armed Shiratsuyu-class destroyers were planned. However, only four, for which the construction of hulls and engines had already been arranged, were to be built, and the remaining ten were to be entirely new types of ships. This decision was also in accordance with Prince Fushimi's instructions. Later known as the Asashio-class, the ten destroyers underwent significant modifications, changing their main guns from flat-firing guns to anti-aircraft guns, doubling the machine guns compared to the Shiratsuyu-class, and adding fire control devices to accommodate anti-aircraft shooting. In exchange, the Asashio-class removed the reloading device and the spare torpedoes stored there, reducing the torpedo count from 16 in the Shiratsuyu-class to 8. However, the most significant changes were in the hull and engine.
During this period, the Imperial Navy recognized that withdrawal from disarmament treaties was only a matter of time. As a result, the Asashio-class hulls were enlarged, marking the first time in the history of Imperial Navy destroyers that they exceeded 2.000 tons. With the enlargement of the hull, not only the armament but also the improvement of seaworthiness and habitability became more achievable. Due to a significant relaxation in speed requirements, from 35 knots to over 30 knots, the boilers were reduced from three to two, and the main engines were also downsized according to output. While the engine volume was significantly reduced, the fuel tanks were enlarged. The Asashio-class's range was substantially improved compared to the Shiratsuyu and Hatsuharu classes, thanks to the efficiency of the engines.
For non-treaty-limited vessels, initially, the Circle 2 Plan considered the construction of multiple oilers and seaplane tenders. These special mission ships were intended to serve as auxiliary forces for regular aircraft carriers, each designed for potential conversion into small carriers. However, even if a 10.000-ton special mission ship were converted, the limited size of the hull would not allow for many aircraft to be carried, and the flight deck would be cramped. Prince Fushimi, who personally held the control stick, knew how difficult and dangerous takeoffs and landings could be.
Even if small carriers were constructed, the pilots assigned there would be limited to those with excellent takeoff and landing skills, and accidents due to the cramped flight deck would likely be unavoidable, even with their expertise. If aircraft operations on small carriers were to be considered, the takeoff run and landing speed would impose extremely strict requirements, undoubtedly compromising the aircraft's performance. Therefore, Prince Fushimi insisted more than anyone else that carriers should be large. In a nutshell, his philosophy was that carriers should dictate the terms to aircraft, not the other way around.
Despite successive revisions to the Circle 2 Plan by Prince Fushimi, he was already looking ahead to the Circle 3 Plan. Premised on escaping the shackles of disarmament treaties, the Circle 3 Plan was expected to have a much larger budget compared to the Circle 1 and Circle 2 Plans.
<Memo>
Amagi-class aircraft carrier (sister ships Katsuragi, Kasagi, Aso, sub-class ships Ikoma, Tsukuba, Ibuki, Kurama)
- Standard displacement: 16.800 tons (notified value to others, actual is 18.400 tons)
- Overall length: 230 meters, beam, 23 meters
- Flight deck: 29,5 meters by 27 meters
- 6 × 12,7 cm twin anti-aircraft guns and 20 × triple 25 mm autocannons
- 6 boilers, 4 shafts, 114.000 horsepower, 31 knots
- Aircraft carried: 60
Due to securing carrier quotas equivalent to the US and the UK at the London Naval Conference, the Circle 1 Plan included the construction of four carriers, and the Circle 2 Plan similarly planned four carriers. These eight carriers were supposed to fit within 16.800 tons during the design phase. However, upon completion, they were nearly 10% overweight. Therefore, the declared displacement to related countries is understated.
Despite the less impressive speed performance due to the broad bow, the flight deck's rectangular shape, and the adoption of an enclosed bow, contribute to the flight deck length being almost the same as the overall length. The four carriers built in the Circle 2 Plan underwent minor improvements, such as a slightly larger bridge compared to the four carriers in the Circle 1 Plan, but there were no significant changes to the hull or engine.
With the commissioning of the lead ships Amagi, Katsuragi, Kasagi, and Aso, the existing carriers Akagi and Kaga were decommissioned, and the Hōshō began conversion into a repair ship.
Asashio-class destroyer (10 ships of the same class)
- Standard displacement: 2.000 tons
- Overall length: 120 meters, beam: 10,5 meters
- 3 × 12,7 cm twin anti-aircraft guns, 4 × twin 25 mm autocannons, 2 × quadruple 61 cm torpedo tubes (without spare torpedoes)
- 2 boilers, 2 shafts, 33.000 horsepower, 31 knots
Unlike traditional torpedo-focused destroyers such as the Fubuki, Hatsuharu, and Shiratsuyu classes, the Asashio-class emphasizes anti-air capabilities. With a smaller engine volume ratio in the hull, it achieves significantly improved endurance and habitability compared to previous ships. Additionally, the placement of the main engine and main boiler in a shifted configuration enhances damage resistance in case of impact.
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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...
