Some persons had the following image of the future, assuming that a Japan-Korea tunnel would be constructed under the Tsushima Straits: Trains would be operated through the tunnel to the Korean peninsula, from Busan Metropolitan City to Hoten (Fengtian) (present Shenyang City), to Shinkyo (Xingjing), the capital of Manchukuo (present Changchun), onward to Beijing City and to Shonan (present Singapore).
また将来的には対馬海峡に日韓トンネルを建設して朝鮮半島へ直通、釜山広域市から奉天（現：瀋陽市）を通り満州国の首都新京（現：長春）、さらには北京市・昭南（現：シンガポール）に至る、という構想も一部では描かれていた。