American negotiators did not enter the ratio dispute blind: the United States had bugged the delegations and knew Japan's internal bargaining limits. The intelligence showed that Japan wanted 10:7 but might accept 5:3 as the bare minimum. Washington used that knowledge to secure the six-ship numerical advantage it wanted rather than to design a settlement with more political margin. The episode turns naval intelligence into part of the treaty's later legitimacy problem, because the successful bargain also maximized Japanese resentment.
Notable Point · 1:00:18-1:00:43
American surveillance revealed Japan's minimum acceptable ratio
American monitoring of the delegations showed that 5:3 was the lowest capital-ship ratio Japan might accept, yet Washington still pressed for that floor.