John Jordan's figures, as summarized in the discussion, put Japan's submarines built, building, or ordered at nearly 83,000 standard tons when the treaty took effect. Japanese planners reckoned that their strategy required at least 78,000 tons, well above the 52,700-ton limit. The Royal Navy was moving in the other direction and giving up on the fleet submarine. A submarine that could not keep pace with surface forces could not fill the role, however attractive the concept appeared on paper. The same treaty ceiling therefore constrained an expanding Japanese requirement while formalizing Britain's retreat from a concept it had struggled to make practical.
Chapter · 26:31-28:40
Japan's submarine requirement and the limits of the fleet submarine
Japan believed its naval strategy required far more submarine tonnage than the treaty allowed, while the Royal Navy was abandoning a fleet-submarine concept that contemporary propulsion could not make practical.