Larger treaty battleships would push Japan beyond Yamato-scale ambitions

How would 42,000-ton British and American battleships affect the Yamato class?

Japan would likely seek an even larger twelve-gun 18-inch design, risking ships too costly and complex to complete.

Japanese qualitative superiority depended on building ships intended to face more than one American opponent. A 42,000-ton British or American standard with twelve 16-inch guns would raise the baseline that Japanese designers were expected to defeat. The projected answer carries twelve 18-inch guns, producing a ship larger and more demanding than Yamato. Japan's industrial and wartime constraints might leave such vessels as unfinished hulls rather than usable battleships. A higher treaty ceiling changes rival design responses and construction risk, not just the dimensions of one British class.