From Japanese Destroyer Captain, by Tameichi Hara (Naval Institute Press, 2013), Kindle Loc. 702-712:
In April 1930, Japan, Great Britain and the United States reached another disarmament agreement in London which established ceilings for auxiliary warships. The 1921 ceilings on capital ships were maintained. This result set Japanese naval officers in a frenzy. They were infuriated at the result which put Japanese naval strength in heavy cruisers, light cruisers, and destroyers at 62, 70, and 70 per cent of the United States. And submarine strength was established at parity by the agreement.
It is difficult today to explain why these results were so unsatisfactory to the Japanese Navy. Japan had insisted on at least 70 per cent of America’s strength in heavy cruisers. And parity in submarines was disappointing because Japan then had 77,900 tons compared with America’s 52,700 tons.
All these arguments later proved silly when American industrial capacity produced naval ships in volume which overwhelmed Japan in the Pacific War. But in 1930, Japanese naval officers argued vehemently about the limitation. They insisted that Japan had been forced to swallow American terms at London. They came then to consider the United States not merely a potential enemy, but a probable enemy. All maneuvers from then on were carried out on the theory that the “hypothetical enemy” was the United States.