The Mogami class illustrates Japan's willingness to design ships for later changes that evaded treaty categories. A further counterfactual applies that willingness to less visible submarines. Submarines could be built or maintained inside enclosed facilities, moved under changing numbers, and hidden more easily from foreign observers than large surface warships. Because Japan produced many components domestically, officials could also attribute material consumption to merchant construction or claimed manufacturing failures. Restrictions on foreign travel and observation in Japan would have made the true submarine total harder to establish. Claims of poor engine reliability could also have encouraged opponents to underestimate the capability of the fleet they could observe.
Notable Point · 2:04:12-2:08:16
Japan's opportunity to conceal extra submarines
Japan's controlled shipyards and opaque industrial reporting made submarines a more practical field for treaty evasion than conspicuous surface ships.