Japan moving first after a failed London framework would set the technical terms of the next building round. An announced 18-inch-gun Japanese design would make British 12-inch, 14-inch, and other small battleship ideas politically and strategically difficult. Britain might answer with a fast design carrying new 15-inch/50 guns supported by existing shell stocks and barrel repair facilities. The United States would likely continue around 16-inch guns in triple turrets.
Notable Point · 1:13:29-1:21:43
Japanese 18-inch ships as the trigger
Japan building an 18-inch-gun capital ship would force Britain and the United States away from smaller treaty-style battleship ideas.