Prelude to the attack on Pearl Harbor

Japan's fear of being colonized and the government's expansionist policies led to its own imperialism in Asia and the Pacific, as it sought to join the great powers, all of which were Western nations.

Planning had been underway for some time on an attack on the "Southern Resource Area" to add it to the Greater East Asia Co-Prosperity Sphere Japan envisioned in the Pacific.

In March 1933 Japan withdrew from the League of Nations in response to international condemnation of its conquest of Manchuria and subsequent establishment of the Manchukuo puppet government there.

Those efforts failed to deter Japan from continuing its war in China or from signing the Tripartite Pact in 1940 with Nazi Germany and Fascist Italy, which officially formed the Axis Powers.

Believing that the American way of life would be endangered if Europe and the Far East fell under fascist military dictatorship, it committed to help the British and the Chinese through loans of money and materiel and pledged sufficient continuing aid to ensure their survival.

[19] The complete U.S. oil embargo reduced the Japanese options to two: seize Southeast Asia before its existing stocks of strategic materials were depleted or submission to American demands.

[14] The American counterproposal of November 26, the Hull note, required Japan to evacuate all of China unconditionally and to conclude non-aggression pacts with Pacific powers.

In the days before the attack, a long 14-part message was sent to the embassy from the Foreign Office in Tokyo that was encrypted with the Type 97 cypher machine, in a cipher named PURPLE.

The final part, with its instruction for the time of delivery, had been decoded Saturday night but was not acted upon until the next morning, according to Henry Clausen[citation needed].

Tōjō argued that yielding to the American demand to withdraw troops would wipe out all the gains of the Second Sino-Japanese War, depress Army morale, endanger Manchukuo and jeopardize the control of Korea.

Hirohito appointed Hideki Tojo instead and was worried, as he told Konoe, about having the Imperial House being held responsible for a war against Western powers on Kōichi Kido's advice.

[26] At the Imperial Conference on November 5, Hirohito approved the plan for a war against the United States, Britain and the Netherlands that was scheduled to start in early December if an acceptable diplomatic settlement were not achieved before then.

[28] On 30 November 1941, Nobuhito, Prince Takamatsu warned his eldest brother, Hirohito, that the navy felt that Japan could not fight more than two years against the United States and wished to avoid war.

After consulting with Kōichi Kido, who advised him to take his time until he was convinced, and Tōjō, Hirohito called Shigetarō Shimada and Nagano, who reassured him that war would be successful.

[29] On December 1, Hirohito finally approved a "war against United States, Great Britain and Holland" during another Imperial Conference, to commence with a surprise attack on the U.S. Pacific Fleet at its main forward base at Pearl Harbor, Hawaii.

[30] Yoshikawa began gathering intelligence in earnest by taking auto trips around the main islands, touring Oahu in a small plane, and posing as a tourist.

[31] Information was returned to Japan in coded form in Consular communications and by direct delivery to intelligence officers aboard Japanese ships calling at Hawaii by consulate staff.

[32] Had they been closed, however, it is possible Naval General Staff, which had opposed the attack from the outset, would have called it off since up-to-date information on the location of the Pacific Fleet, on which Yamamoto's plan depended, would no longer have been available.

For the next several months, planning and organizing a simultaneous attack on Pearl Harbor and invasion of British and Dutch colonies to the south occupied much of the Japanese Navy's time and attention.

On the other hand, Hawaii's distance meant a successful surprise attack could not be blocked or quickly countered by forces from the Continental U.S. Several Japanese naval officers had been impressed by the British action at the Battle of Taranto in which 21 obsolete Fairey Swordfish disabled half the Regia Marina, the Italian Navy.

Admiral Yamamoto even dispatched a delegation to Italy, which concluded a larger and better-supported version of Cunningham's strike could force the U.S. Pacific Fleet to retreat to bases in California, which would give Japan the time needed to establish a "barrier" defense to protect Japanese control of the Dutch East Indies.

[citation needed] Japanese strategists were undoubtedly influenced by Admiral Heihachiro Togo's surprise attack on the Russian Pacific Fleet at the Battle of Port Arthur in 1904.

[36] In a letter dated January 7, 1941, Yamamoto finally delivered a rough outline of his plan to Koshiro Oikawa, the Navy Minister, from whom he also requested to be made commander-in-chief of the air fleet to attack Pearl Harbor.

A few weeks later, in yet another letter, Yamamoto requested for Admiral Takijiro Onishi, chief of staff of the Eleventh Air Fleet, to study the technical feasibility of an attack against the American base.

After first consulting with Kosei Maeda, an expert on aerial torpedo warfare, and being told that the harbor's shallow waters rendered such an attack almost impossible, Onishi summoned Commander Minoru Genda.

In September 1941, Commander Yasuji Watanabe of the Combined Fleet staff estimated two divisions (30,000 men) and 80 ships, in addition to the carrier strike force, could capture the islands.

[40] Although the idea gained some support, it was soon dismissed for several reasons: With an invasion ruled out, it was agreed that a massive carrier-based three wave airstrike against Pearl Harbor to destroy the Pacific Fleet would be sufficient.

In addition, the Advanced Expeditionary Force included 20 fleet and five two-man Ko-hyoteki-class midget submarines, which were to gather intelligence and sink U.S. vessels attempting to flee Pearl Harbor during or soon after the attack.

[46] On December 1, 1941, after the striking force was en route, Chief of Staff Nagano gave a verbal directive to the commander of the Combined Fleet, Admiral Isoroku Yamamoto, to inform him: Japan has decided to open hostilities against the United States, United Kingdom, and the Netherlands early in December.... Should it appear certain that Japanese-American negotiations will reach an amicable settlement prior to the commencement of hostilities, it is understood that all elements of the Combined Fleet are to be assembled and returned to their bases in accordance with separate orders.

Additionally, aircraft were parked on airfields to lessen the risk of sabotage, not in anticipation of air attack, in keeping with Short's interpretation of the war warnings.