Six-inch guns occupy a useful naval firepower tier

Would fitting twin 6-inch guns to a cruiser trigger a naval arms race or simply look like one country's eccentric choice?

It would be watched and perhaps copied, but existing guns above 5 inches make a sudden arms race unlikely; 6 inches remains an attractive balance of shell weight, damage, and rate of fire.

Several navies already operate guns larger than 5 inches, so the first new 6-inch installation would not emerge into an empty field. The caliber combines a heavier shell with a still-useful rate of fire, making it a recurring design threshold. Other navies might follow if the installation proved effective, but that is different from an automatic competitive spiral. Even larger weapons, including 9.2-inch guns, could reappear for particular missions.