Coastal superguns could become a naval-treaty loophole

How would treaty powers react if a nation built very large coastal guns using battleship-sized turrets?

They would treat it as a serious loophole and eventually demand either comparable rights or treaty restrictions.

Britain or Japan had the most plausible 1920s industrial base for 18- to 22-inch coastal weapons. Calling them land defenses could preserve turret and gun-making skills while appearing to remain outside battleship limits. British emplacements at Dover, Gibraltar, or Singapore could then influence later operations, including the Channel Dash or the defense of Malaya. Rival powers would not tolerate the loophole indefinitely and would seek equal rights or a treaty prohibition. The scenario demonstrates how arms-control categories can redirect rather than eliminate military technology.