Why a Japanese-sponsored treaty-evasion yard would be hard to conceal

Could Japan covertly finance another country's shipbuilding industry to evade interwar treaty restrictions?

Only a few countries possessed enough existing heavy industry to be plausible, and that narrow candidate list would make Japanese sponsorship difficult to conceal from the treaty powers.

Capital-ship construction requires enough specialized industry that the treaty powers would probably identify the sponsor. Spain's suitability is disputed: its domestic hull construction is set against its reliance on British machinery, weapons, design work, and skilled personnel. Brazil's existing foundries offer a starting point, although its ability to supply the full industrial chain is also challenged. Sweden and the Netherlands are stronger technical candidates, but Japan would struggle to control them financially. The Soviet Union has relevant capacity but is rejected as a plausible Japanese partner.