After 1918, when the Japanese immigration to the Philippines set in, most Americans sold their land to the Nipponese or hired Japanese as farm managers. So, when the invasion came in 1941, the Japanese found 20,000 of their countrymen already settled in and familiar with Mindanao roads, resources, and the whereabouts of Americans on the island. Japanese who worked in the fields went into the ranks when the Japanese Army came. This was long-range planning by the Japanese.
From the Philippine iron mines, ore was going to Japan at the rate of nearly 1,192,000 tons a year in pre-war times. On the Surigao Peninsula of Mindanao lies one of Asia's largest known iron deposits, estimated at 1 billion tons.
When the Philippine gold boom started in 1935 and the islands became one of the world's leading gold producers, prospectors flocked to Mindanao and by 1941, the Philippine Islands had become one of the world's greatest gold producing regions. The Japanese would end up working these gold mines for over 3-1/2 years while they occupied the islands.
Just before noon on December 8, 1941, Japanese bombers destroyed half of the U.S. Army Air Force on the ground at Clark Field, north of Manila and seized air superiority over the Philippines. The Japanese seized the southern Philippines not only for the iron and gold mines, but also for it's strategic location. There they massed naval forces at Davao for the invasion of the Dutch East Indies.
Of all the materials Japan's Merchant Marines brought to the homeland, none was more crucial than oil. In fact, the main reason the Japanese went to war was because of the oil embargo against them. As the Japanese war machine continued to steamroll through countries, the Japanese turned their eyes to the extensive oil fields of the Dutch East Indies. In 1940, the Dutch colony produced just under 8 million tons of petroleum. In 1941, Japanese planners expected the Dutch and British to demolish these walls as they retreated. The Japanese managed to restore production up to 78% of 1940 levels in two years. Tankers brought in 82% of the petroleum needed to drive the Imperial Army and Navy. The Japanese knew they needed a quick victory or all would be lost. The length of the war and the increasing U.S. submarine attacks on merchant ships and tankers stopped the flow of oil and slowed down a fast-moving Japan.
Warned by Pearl Harbor code breakers of Yamamotos' coming invasion in 1942 at Midway, the U.S. forces prepared an ambush on the Japanese fleet. The U.S. striking force managed to sink major carriers and heavy cruisers, resulting in an American victory. The battle of Midway in June 1942 turned the tide of the war.
Japan's hope of winning the war began to slip from their grasp. U.S. forces continued to sink merchant ships and tankers, causing Japan's war vessels to be used in moving much needed natural resources. Until 1942, the loot of conquered nations was shipped directly to Japan; after that, the pressure from American Naval forces in the Pacific caused the loot to be shipped to the Philippines for safekeeping. The Philippines offered a safe repository for the gold. An elite Japanese engineering battalion systematically buried the accumulated fortune throughout the Philippines, in hundreds of different locations in order to protect this huge hoard of gold. General "Tiger of Malaya" Yamashita, whose name was given to the buried treasure, surrendered on August 15, 1945 in the Philippines, after loosing 200 thousand men. General Tomoyuki Yamashita was hanged in 1946 for war crimes. In truth, General MacArthur was taking revenge on what was probably the best general the Japanese had, for the humiliation the Japanese had caused him early in the war.
Admiral Kodama, a member of the Dark Ocean Society, in charge of looting all the conquered countries and the real force behind the burial of the treasure, paid a $200 million bribe (in gold bullion) to the OSS and was released, as well as about 50 of his closest friends and allies. He returned years later to the Philippines to retrieve some of the buried gold.
