Why a treaty-era capital ship could not remain secret

Cruiser aircraft and naval patrols created many opportunities to discover activity at remote Pacific bases, especially when treaty restrictions made powers alert to unauthorized development. Shooting at an overflying aircraft or an investigating cruiser would reveal the secret and might start a war before the hidden ship was ready. Established shipyards were also observable by naval attaches, leaving no easy place for a major capital ship to disappear. Constructing a secret yard would require conspicuous machinery, skilled workers, transport, and a supporting population. The industrial and human footprint therefore defeats the premise even before the warship enters service, making secret-battleship scenarios a poor foundation for a close-to-history counterfactual.