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Pearl Harbor and War in Southeast Asia

Japan Plans War against the United States | Mlitary Readiness in the United States, to June 1941 | Steps Toward War, July to December 1941 | The Attack at Pearl Harbor and the Philippines | Passion, Rumors and Myth in the United States | IInternment of Japanese-Americans

Admiral Yamamoto

Admiral Yamamoto. Click for details.

Map of Japanese controlled areas in 1940

Japanese controlled areas during the
stalemate of 1940, in yellow. Click for minor enlargement. Enlarged map of Japanese controlled areas in 1940

Pearl Harbor attack

Pearl Harbor Attack

Japan Plans War against the United States

By 1940, the war between the Chinese and Japanese had bogged down into a stalemate. The Chinese were unable to make military gains in driving the Japanese from their homeland, but their resistance had stopped the Japanese. Japan's offensive was proving to be a failure. In response, the frustrated Japanese tried harder. They started the "Three Alls Policy" – kill all, loot all, burn all (三光政策). They followed the same course that Germany followed during World War I. Rather than admit failure and withdraw to Manchuria, they chose more offense. The Japanese were proud. Japanese warriors don't withdraw for the sake of peace and for anything less than their goal in war.    

In March 1940, Japan's parliament, the Diet, unanimously passed a declaration of support for holy war against China, and in the spring of 1940 the Japanese launched a new offensive there. Hostility toward Japan increased among Americans, and some began to wonder about the scrap metal, oil and other materials that American businesses were selling to Japan.

In May 1940, the U.S. Navy moved the base of its Pacific Ocean fleet from San Diego to its "impregnable" naval base at Pearl Harbor in the Hawaiian Islands. Admiral Yamamoto, commander of Japan's Combined Fleet since August 1939, described this as "tantamount to a dagger pointed at our throat." (Journal of American-East Asian Relations, Fall 1994, "The Pearl Harbor Raid Revisited.")

In the summer of 1940, Germany's military rolled over the French and Dutch in Europe, and Japanese strategists were concerned that the victorious Germans might wish to re-establish a presence in the South Pacific. Germany's successes encouraged Japan to expand into the Southeast Asia and the South Pacific region. Japan was using around 28,000 gallons of oil a day in China, and it needed steel for its war machine. For the sake of "imperial self-sufficiency," Japan was interested in acquiring secure oil supplies and other materials from European-ruled Southeast Asia – the Dutch in the Indonesian Archipelago, the British in Malay and northern Borneo, and the French in Indochina.

With Germany threatening Britain, Japan's strategists saw Britain as too occupied to defend its interests in East Asia. There was the problem of the Americans, but on July 2, Japan's leaders met at one of their Imperial Conferences and decided not to be deterred by the possibility of war with the United States in fulfilling their ambitions. They affirmed their commitment to victory in China and to building a "Co-Prosperity Sphere" in East Asia.

The Japanese bargained with the weakened French and won permission to move into northern Vietnam, which they did on September 22. From here they began bombing southwest China, adding to their blockade against Chiang Kai-shek's forces. Hirohito was bothered by what he saw as his nation acting dishonorably, "like a thief after a fire," taking advantage of France after its defeat. But he went along with it, not wishing to be out-of-step with what was seen as necessary for Japan's war effort.

The United States responded to Japan's move into Indochina by abrogating America's commercial treaty with Japan. President Franklin Roosevelt's administration embargoed scrap iron and steel that U.S. companies had been selling to Japan -- nearly seventy percent of Japan's supply of these materials. Roosevelt encouraged the Dutch in Indonesia to stop selling oil to Japan, while allowing U.S. sales of oil to Japan to avoid pushing the Japanese into war with the U.S. and to keep oil as a bargaining lever against the Japanese.

The Japanese responded to Germany's call for a pact. Japan had been reluctant to tie itself to European conflicts but now saw advantage in it. On September 27, 1940, Japan signed a treaty with Germany and Italy – the Tripartite Pact. Japan, Germany and Italy promised to join either of the other two should one of them go to war against any power not presently at war – a pact aimed against the United States. Joining the pact in late November was Hungary, Romania and Slovakia. Bulgaria was to join on March 1, 1941.

Following the signing of the Tripartite Pact, the U.S. State Department ordered all Americans to return home from the Far East – except for military personnel, mainly in the Philippines. The British announced that they would open a road through Burma, north to Chongqing, to overcome Japan's blockade from northern Vietnam, and Tokyo threatened to declare war on Britain.

Hoping to cripple Britain, Germany was trying to encourage Japan to move against the British at Singapore – the island and naval base at the southern tip of the Malay Peninsula. Germany's foreign minister, Ribbentrop, advised Japan's military attaché in Berlin that while moving south "the best way to keep America out of the war" would be not declaring war.

The Japanese told the Germans that preparations for taking Singapore would be completed by the end of May and that war with the United States could not be ruled out. Meanwhile, Admiral Yamamoto was concerned that when Japan moved against Singapore and into the Indonesian Achipelago, the U.S. could send its forces out from Pearl Harbor and hit Japan's forces on their flank.

In early 1941 Yamamoto announced to his colleagues that simultaneous with Japan's invasion of Southeast Asia and the unhappy event of a war with the United States, Japan should cripple America's Pacific fleet by an air offensive. This he believed would damage American civil and military morale, perhaps to the point of rendering the Americans helpless and would prevent the U.S. from launching "disturbing air strikes" against Japanese cities. Such a mission against the Americans, Yamamoto admitted, would be risky and, with much at stake, divine assistance would be needed.

Japanese strategists saw the U.S. Pacific Fleet at Pearl Harbor also as a threat to their shipping lanes, and they saw a need to eliminate U.S. bases in the Philippines and Guam – which would be a threat to shipping oil from Indonesia to the Japanese homeland.

Invading Hawaii with troops was rejected, although it would have given the Japanese greater control over the Pacific. Japanese intelligence was over-estimating the size of the American forces in the Hawaiian Islands. The Japanese believed they could not spare troops from their invasion to the south, and adding troop transports to the strike force against Hawaii would slow it to eight knots and, they believed, perhaps cause its detection by the United States. 


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