Synthetic fuel, railways, and submarines for Japan

Coal-to-oil plants would reduce Japan's fuel vulnerability, while quickly built narrow-gauge railways could shift domestic cargo away from coastal convoys. That would ease demand on an escort fleet already too small for the coming war. A larger merchant navy would help, but Japan cannot expand every category with the same limited industry. More submarines support the attritional phase intended to weaken an approaching American fleet before the decisive battle, while smaller yards can build escorts without displacing capital-ship and carrier work in major naval yards. The proposed railways are deliberately austere, using concrete sleepers and a limited service life to gain useful capacity before the expected war.