It made no sense for lots of reasons.
Had the war not come, Japan would have bankrupt itself spending on these massive ships. Japan lacked the industrial capacity to compete with the United States; indeed, even if it had managed to seize and keep wide swaths of East Asia, it could not have matched U.S. industrial production for decades. The United States would have responded to Japanese construction with even larger, more deadly ships, and of course eventually with submarines, aircraft and guided missiles.
In January 1936 Japan announced its intention to withdraw from the London Naval Treaty, accusing both the United States and the United Kingdom of negotiating in bad faith. The Japanese sought formal equality in naval construction limits, something that the Western powers would not give. In the wake of this withdrawal, Japanese battleship architects threw themselves into the design of new vessels. The first class to emerge were the 18.1-inch-gun-carrying Yamatos, the largest battleships ever constructed. However, the Yamatos were by no means the end of Japanese ambitions. The Imperial Japanese Navy (IJN) planned to build another, larger class of super battleships, and had vague plans for even larger ships to succeed that class. War interceded, but had Japan carried out its plans it might have deployed monster battleships nearly as large as supercarriers into the Pacific.
The A-150 class would have superseded the Yamatos, building on experience with that class to produce a more formidable, flexible fighting unit. Along with the Yamatos, these ships were expected to provide the IJN with an unbeatable battle line to protect its Pacific possessions, along with newly acquired territories in Southeast Asia and China.
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