The importance and vulnerability of Japan's railroad system (see Appendix "B")4. With the progressive deterioration of the Japanese shipping situation, a greater burden is being thrown upon the highly organised but relatively limited railroad system. The main rail line from North China across southern Manchuria and down through Korea carries a very substantial part of the pig iron, coal, and other essential materials imported by Japan Proper from these areas. Rail traffic in Japan Proper is likewise of the highest importance to the main industrial areas as regards the transport of raw, semi-finished and finished products between the various war centres.