WWII: tonnage of tankers built by Japan and sunk by the U.S. 1942-1945

With little fossil fuel resources of its own, Japan has largely depended on foreign petroleum imports for more than a century. Throughout the 1930s, imports from the United States fulfilled over 80 percent of Japan's oil needs, however, growing tensions between the two powers in the wake of Japan's invasion of China in 1937 saw the U.S. gradually cut trade ties with Japan. The U.S. was reluctant to cease this oil supply as it believed this would be taken as an act of war, but after Japan seized control of airfields in French Indochina (therefore blocking U.S. supply routes into China), the U.S. placed an oil embargo on Japan in August 1941.

Japan's next invasion

Japan's oil demand was already very high due to its military actions in China, and the U.S. believed that this move would bring the invasion to a halt. However, it had the opposite effect. On December 8, 1941 (Dec. 7 for Pearl Harbor due to time differences) Japan launched a full-scale invasion of Southeast Asia and the Pacific, with the intent of capturing the oil-rich regions of the Dutch East Indies and Burma. Europe's colonial powers were too preoccupied by war at home to respond effectively, and the attack on Pearl Harbor had temporarily neutralized the U.S. Navy's Pacific Fleet - within six months, Japan controlled virtually all of Southeast Asia.

A new dilemma

By mid-1942 Japan was in possession of the East Indies, the region's largest oil producer, but it now had to transport this oil roughly 6,000 kilometers to the metropole or China - a role that had previously been fulfilled by Western powers. A tanker manufacturing program was started immediately, with most Japanese oiler classes having a displacement between 10,000 and 20,000 tons each. In 1942, the U.S. Pacific Fleet became operational once more, but it was not until 1943 that U.S. submarines began aggressively targeting these new Japanese oilers. This campaign proved to be an enormous success, with Japanese losses exceeding production each year between 1943 and 1945. Without these actions, the Japanese may have been able to strengthen their position in the Pacific or push further into China and Burma, as the disruption of Japan's oil supply greatly weakened its ability to transport manpower and resources, or to run its tanks, aircraft, and navy.