Pearl Harbor (World War II)

For the geographic area, see Pearl Harbor

On December 7, 1941, units of the Imperial Japanese Navy conducted air and submarine operations against American forces in the Battle of Pearl Harbor. This battle was a key element in the major Japanese escalation of what they call the Pacific War.

While the United States had intelligence suggesting a high probability of Japanese attacks in December 1941, and some specific information that either did not reach the Pearl Harbor commanders, Admiral Husband E. Kimmel (Navy) or Lieutenant General Walter Short (Army), the attack was a tactical surprise.

Few battles, and the circumstances leading to them, have been studied as extensively as this one. Many concepts of the discipline of intelligence and warning resulted from this action.

Background

Relations between the United States and Japan were tenuous at best since the First World War. Japan's Twenty-One Demands threatened U.S. interests but were tolerated. Japan's position at the Washington Naval Conference was recognized although not to the extent that Japan nationalists would have liked (they saw any situation not at parity with Great Britain and the U.S. as an insult). The Nine-Power Treaty was somewhat as a compromise; signatory nations agreed to abide by the Open Door Policy while the territorial integrity of China was to be respected. Japan, though, in the 1930s began a series of Manchurian Incidents by which it claimed the right to exact military retribution against China. The first of these incidents was the Mukden Incident after which Japan took over all of Manchuria and established the puppet state of Manchukuo. Subsequent incidents led the Japanese army to invade parts of Northern China. Japan also occupied for a time Shanghai, and following a protest by the League of Nations, Japan withdrew from the League.

By the summer of 1937 Japan had seized Chinese territory to the outskirts of Beijing. Following the Marco Polo Bridge Incident, Japan began a prolonged war against China resulting in invasions along the southern coast. Shanghai was attacked and severely devastated. In December, Japanese forces invaded the Chinese capital at Nanking and perpetrated massive crimes.

In response to this aggression against China, as well as the aggressions of Italy against Ethiopia, the aggressive expansion on Nazi Germany in central Europe (see Re-Occupation of the Rhineland), and Italy's and Germany's support of Franco's Felange in the Spanish Civil War, U.S. President Franklin D. Roosevelt gave a speech in which he urge a policy of moral and economic quarantine against these belligerent nations. It was one of Roosevelt's few foreign policy speeches during the Great Depression and was not well received by the American public. Roosevelt retracted the statements. Nonetheless, to the Japanese the reverse looked like U.S. weakness. This belief was reinforced in December when Japanese bombers sunk the USS Panay and three other U.S. vessels on the Yangtze River. Because of poor American response to his Quarantine speech, the U.S. had gone to war over such incidents in the past, Roosevelt accepted a weak Japanese apology and a $2M indemnity.

Following the German defeat of France in 1940, Japan saw opportunity to further squeeze China. It prevailed on the Vichy French government to allow Japan to occupy and use airbases in Northern French Indochina from which it could bomb China and interdict the flow of western aid to China through French Indochina. The U.S., in response, authorized a loan to China and passed the Export Control Act which authorized the president to restrict the export of strategic materials to nations he deemed threatened national security. Roosevelt used the act to embargo aviation fuel, scrap steel, and other materials to Japan.

In September 1940, Japan entered the Tripartite Pact with Germany and Italy pledging to aid each other if attacked by another power. Given that Germany was already planning its war against the Soviet Union and Japan in April 1941 reached a non-aggression pact with Stalin, that "other power" could only have meant the United States. In July 1941, Japan seized all of French Indo-China. Roosevelt extended the embargo to cover all petroleum exports, a serious step as Japan imported between 80 and 90 percent of its oil from the United States. In order to continue its war in China, Japan would need to become self-sufficient in these strategic resources.

Negotiations between the United States and Japan proved unproductive. Secretary of State Cordell Hull maintained an inflexible position that the first step in any resumption of trade between the U.S. and Japan would be a complete withdrawal of Japanese forces from French Indochina, a step that the militant nationalists controlling Japan were unwilling to take. Their other alternative was to seize the oil fields of the Dutch East Indies, an alternative for which they began war plans. In order to secure their lines of supply between Indonesia and Japan, they would need control of the British base at Singapore and the U.S. colony of the Philippines. Invasion of the Philippines, the Japanese correctly figured, would lead to war with the U.S., and given the strength of the U.S. navy in the Pacific as well as the productive capacity of the United States, the best hope for a Japanese victory in this war would be a decisive victory from which the U.S. would have little other alternatives than to negotiate a peace. To decisively defeat the U.S. fleet, would require a massive blow at a time when the U.S. Navy was least prepared and least expecting a Japanese attack: at the very beginning of the war. And because the U.S. Pacific Fleet was stationed at Pearl Harbor, this became the target for the first Japanese attack of World War Two.

U.S. intelligence and planning

Threat assessment

Sabotage vs. air attack

Short was convinced that the major threat to his aircraft was sabotage by residents of Japanese ancestry, so he had them parked in close formation for ease in guarding them against ground attack. This made them dense targets for strafing and bombing.

Implications of the Battle of Taranto

In 1940, the Royal Navy, at the Battle of Taranto, delivered a devastating night attack, by torpedo aircraft, to battleships in a harbor. The U.S. Navy, in spite of knowing the details of that attack, still believed its ships were safe from aerial torpedoes in a harbor, although Taranto was as shallow as Pearl.