Germany needed to arrange closer relations with the Soviet Union, if not just for economic reasons alone. Despite work on coal hydrogenisation, Germany lacked oil and could only supply 25% of its own needs. Since its main supplier, the United States, would be potentially cut off during a war, Germany had to look to Soviet Union and Romania. Germany suffered from the same supply problems for metal ores such as chrome, tungsten, nickel, molybdenum, and manganese, all of which were needed for hardened steel used in tanks, ships and other war equipment. For example, Germany was almost 100% reliant on imports for chrome, and the loss of South African and Turkish imports alone were a blockade to arise would eliminate 80% of imports. Even for manganese, of which Germany supplied 40% of its needs, the expected British blockade would cut its link to its main outside supplier, South Africa. Germany was 35% self-sufficient for iron ore, but would lose 36% of its previous imported supply on the outbreak of war. Furthermore, Stalin's permission was needed to transit tungsten and molybdenum from China, which required Soviet-controlled rail lines. Meanwhile, the Soviet Union was the world's largest source of manganese, the second largest for chrome and platinum and the third largest supplier of crude oil, iron ore and nickel. Rubber was particularly troublesome, with Germany requiring 80% of its rubber from imports. Hitler required Soviet help to procure rubber from the Far East, the shortage of which had caused Germany problems in World War I. Rubber production in Malaya and the East Indies was dominated by the British and the Dutch. Cutting off these sources would leave Germany with stockpiles for only two months. Although German synthetic materials plants could produce 50% of German rubber needs, Germany still required large amounts of natural rubber as raw material. And just to achieve that synthetic production, Germany had invested a massive 1.9 billion Reichsmarks over three years—almost half of all investment in its capital goods industry. While Germany had decreased its dependence on imported food from 35% in 1927 to 13% in 1939, 40% of its fat and oil food requirements had to be met by imports. Moreover, Germany's food requirements would grow further if it conquered nations that were also net food importers. Soviet imports of Ukrainian grains or Soviet trans-shipments of Manchurian soybeans could make up the shortfall. In 1936, Hermann Göring