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Chapter 6 - Circle 4 Plan

The Ship's Intelligence Lexicon contains the Circle 1, Circle 2, Circle 3, and Circle 4 Plans that have been developed by the Imperial Navy so far. Furthermore, there were various detailed plans like Temporal Plan, Rapidly Plan, and Additional Plan, among others.

As Vice Admiral Yamamoto deciphered these plans, he found that the later the plans were, the less priority was given to battleships, heavy cruisers, and other large surface combatants, and the more emphasis was placed on aircraft carriers and escort vessels. The expansion of base air units was also notable. One got the impression that the Japanese lost a large number of carriers and planes in the first six months or so of the war, and were in a hurry to replenish them.

In any case, in the event of war between Japan and the United States, it seemed that the nature of the conflict would shift from surface gun and torpedo battles to maritime aerial combat or naval escort warfare. Presumably, the main objective of each plan was to strengthen forces to counter the naval interdiction strategy initiated by the US. If viewed from the opposite perspective, the US likely adopted a tactic of besieging Japan which is heavily dependent on overseas resources by disrupting its maritime supply lines. The obvious means for this attack involved a large number of aircraft and numerous submarines.

Yamamoto felt a deep sense of relief that the Yamato and Musashi were not constructed under the Circle 3 Plan. He regretted not believing Hiranuma's words over the years. If the Ship's Intelligence Lexicon had been utilized during Circle 1 and Circle 2 planning, it could have saved the construction of expensive cruisers like the Mogami and Tone classes. Instead, the budget could have been used to significantly enhance airpower and naval escort forces, including coastal defense ships and anti-submarine vessels. The budget for six 10.000-ton cruisers would have been of tremendous benefit.

However, regretting the past was unproductive. Accepting it as a sunk cost or a costly lesson, Yamamoto turned his attention to the Circle 4 Plan. Notably in the overall budget of nearly 1,6 billion yen, two large battleships and one large aircraft carrier stood out.

The combined construction cost for the Yamato-class battleships (presumably Shinano and No. 1111) and the carrier named Taihō exceeded 360 million yen. Additionally, several cruisers of 6.000 and 8.000 tons were planned, collectively inflating the budget to more than a hundred million yen.

'Except for the carriers, everything else is a waste!'

Considering that the war was clearly shaping up to involve maritime aerial combat or naval escort warfare, constructing large battleships and outdated vessels like torpedo squadrons or destroyer leaders was nonsensical.

'Torpedo squadrons or destroyer leaders, if deemed necessary, could be addressed by disbanding the 6th Cruiser Division. As for command cruisers for the submarine flotilla, they would likely become easy targets for enemy submarines or aircraft.'

When this realization struck, decisive action was taken. The construction of Shinano, No. 111, and Taihō was canceled immediately. Furthermore, four Type B cruisers and two Type C cruisers were removed from the Ship's Intelligence Lexicon. Instead, Yamamoto, after some contemplation, allocated the budget to record four Shōkaku-class carriers in the ledger.

'The ship names are arbitrary. Daikaku, Unkaku, Hōkaku, and Ryūkaku should be fine.'

Yamamoto's dilemma lay in whether to design the aircraft carrier as the Taihō class or the Shōkaku class.

The Taihō design addressed a major weakness of aircraft carriers by adding armor to the flight deck, providing exceptional resistance compared to conventional carriers. On the other hand, the Shōkaku design, while lacking in defense compared to the Taihō, boasted a higher aircraft capacity. Additionally, the Shōkaku-class had likely accumulated considerable expertise as it was also being constructed under the Circle 3 Plan. Considering the start of construction and the time of completion, the Taihō design could not be ready until after 1944, even if rushed. However, with the Shōkaku-class, it could potentially be expedited by about six months. During wartime, that half-year held a value equivalent to five or even more than ten years in peacetime. This factor was decisive.

Furthermore, Yamamoto hesitated slightly about the number of carriers to be constructed. Currently, within Japan, facilities capable of constructing the Shōkaku-class were the shipyard at Yokosuka Naval Arsenal and the dry dock at Kure Naval Arsenal, along with four private shipyards in Kobe and Nagasaki. Moreover, by 1940, dry docks exceeding 300 meters would be completed in Yokosuka and Sasebo, making it possible to construct six Shōkaku-class carriers if desired. Comparing the cost of constructing six Shōkaku-class carriers and six cruisers with the two large battleships and one armored carrier in the Circle 4 Plan, the latter clearly incurred lower costs. Even so, Yamamoto limited the number to four carriers, recalling the existence that needed prioritized development.

That was the conversion of the submarine tender Taigei and three seaplane tenders along with two high-speed oilers into aircraft carriers. Although each of these conversions involved extensive engine modifications, they would still be completed much faster than building from scratch. All these vessels were expected to be operational by the declared start of war on December 8, 1941, as mentioned by Hiranuma. Even after converting four Shōkaku-class carriers and six special service vessels into carriers, there was still a surplus budget, which could be allocated to the development of radar, new weapons, and additional aviation funds.

Separately, Yamamoto canceled the construction of vessels oriented towards gun and torpedo warfare, changing all destroyers from torpedo warfare-specialized Type A to anti-aircraft Type B. The budget intended for these vessels was redirected to those deemed useful for maritime aerial combat and naval escort warfare. As a result, the destroyer plans were halted, with the Kagerō-class destroyers reaching a total of fourteen ships, including the measures taken in the Circle 3 Plan. The budget and resources earmarked for construction were redirected towards the Akizuki-class destroyers.

Additionally, Yamamoto would later regret something about the Circle 4 Plan—the naming of one of the carriers he assigned with an arbitrary name that happened to closely resemble that man's name.