Manchurian production remained exposed to shipping

Japan historically favored acquiring resources abroad over investing solely in home-island production. Manchuria offered coal and room for synthetic-fuel development, but building there also placed capital and infrastructure away from the industries that would consume the output. Fuel and chemical products still had to travel by ship to Japan, preserving dependence on vulnerable sea lanes. Blockade and submarine attack could sever the connection between nominal production capacity and domestic use. The location and transport connections of production mattered as much as the amount produced.