Who leads an Anglo-American war against Japan?

Japan's numerical problem extends beyond facing Britain or the United States separately. Neither Anglo-American power could accept the other defeating Japan alone, because the victor would become dominant in the Far East. The partner engaged first would likely shape coalition strategy when the other joined. An American-led plan might drive across Pacific islands toward the Japanese home islands while British forces, operating from Singapore, relieve the Philippines. This is explicitly a counterfactual division of effort, but it shows how basing and coalition politics determine fleet employment.