The historical 5:5:3 framework gave Japan three-fifths of American strength, while Japanese leaders wanted seven-tenths. They feared isolation after the end of the Anglo-Japanese Alliance and sought a fleet strong enough to make an opening attack prohibitively risky. The ratio could not overcome British or American industrial depth in a long war, but it could deny either power confidence in a quick first-round victory. Japan's relatively successful First World War experience also differed sharply from Europe's trauma, helping explain why the same treaty bargain looked different in Tokyo.
Chapter · 15:52-21:54
Japan's security case for a 7:10 fleet ratio
Japan sought enough strength to make an American attack uncertain, while recognizing that superior American industry would prevail in a long war.