Prelude to the attack on Pearl Harbor

A series of events led to the attack on Pearl Harbor. War between the Empire of Japan and the United States was a possibility each nation's military forces had planned for after World War I. The expansion of American territories in the Pacific had been a threat to Japan since the 1890s, but real tensions did not begin until the Japanese invasion of Manchuria in 1931.

Japan's fear of being colonized and the government's

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.

The

Planning for the attack on Pearl Harbor had begun very early in 1941 by Admiral Isoroku Yamamoto. He finally won assent from the Naval High Command by, among other things, threatening to resign. The attack was approved in the summer at an Imperial Conference and again at a second Conference in the autumn. Simultaneously over the year, pilots were trained, and ships prepared for its execution. Authority for the attack was granted at the second Imperial Conference if a diplomatic result satisfactory to Japan was not reached. After the Hull note and the final approval by Emperor Hirohito, the order to attack was issued in early December.

Background

Both the Japanese public and the political perception of American antagonism began in the 1890s. The American acquisition of Pacific colonies near Japan and its brokering of the end of the Russo-Japanese War via the Treaty of Portsmouth, which left neither belligerent, particularly Japan, satisfied, left a lasting general impression that the United States was inappropriately foisting itself into Asian regional politics and intent on limiting Japan, and set the stage for later more contentious politics between the two nations.^[3]

Tensions between Japan and the prominent Western countries (the United States, France, the United Kingdom, and the Netherlands) increased significantly during the increasingly militaristic early

In the 1930s, Japan's increasingly expansionist policies brought it into renewed conflict with its neighbors, the Soviet Union and China. The latter was in 1922 disappointed by Germany's former Chinese colony of

Japan's 1937 attack on China was condemned by the U.S. and by several members of the League of Nations, including the United Kingdom, France, Australia, and the Netherlands. Japanese atrocities during the conflict, such as the notorious Nanjing Massacre that December, further complicated relations with the rest of the world. The U.S.,^[b] the United Kingdom,^[c] France^[d] and the Netherlands^[e] all possessed colonies in East and Southeast Asia. Japan's new military power and willingness to use it threatened the Western economic and territorial interests in Asia.

In 1938, the U.S. began to adopt a succession of increasingly-restrictive trade restrictions with Japan, including terminating its 1911 commercial treaty with Japan in 1939, which was further tightened by the

Japan would take advantage of

At least as early as October 8, 1940,... affairs had reached such a state that the United States would become involved in a war with Japan.... 'that if the Japanese attacked Thailand, or the Kra Peninsula, or the Dutch East Indies we would not enter the war, that if they even attacked the Philippines he doubted whether we would enter the war, but that they (the Japanese) could not always avoid making mistakes and that as the war continued and that area of operations expanded sooner or later they would make a mistake and we would enter the war.'^[9][10]

Japan and the U.S. engaged in negotiations in 1941 in an effort to improve relations. During the negotiations, Japan considered withdrawal from most of China and Indochina after it had drawn up peace terms with the Chinese. Japan would also adopt an independent interpretation of the Tripartite Pact and would not discriminate in trade if all other countries reciprocated. However, War Minister General Hideki Tojo rejected compromises in China.^[14] Responding to Japanese occupation of key airfields in Indochina (July 24) after an agreement between Japan and Vichy France, the U.S. froze Japanese assets on July 26, 1941, and on August 1, it established an embargo on oil and gasoline exports to Japan.^[15][16][17] The oil embargo was an especially strong response because oil was Japan's most crucial import, and more than 80% of Japan's oil came from the United States.^[18]

Japanese war planners had long looked south, especially to Brunei for oil and Malaya for rubber and tin. In the autumn of 1940, Japan requested 3.15 million barrels of oil from the Dutch East Indies but received a counteroffer of only 1.35 million.^[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.^[20] Moreover, any southern operation would be vulnerable to attack from the Philippines, a U.S. colony, and so war against the U.S. seemed necessary in any case.^[21]

After the embargoes and the asset freezes, the Japanese ambassador to the United States, Kichisaburō Nomura, and U.S. Secretary of State Cordell Hull held multiple meetings to resolve Japanese-American relations. No solution could be agreed upon for three key reasons:

1. Italy in the Tripartite Pact
   .
2. Japan wanted economic control and responsibility for southeast Asia, as envisioned in the Greater East Asia Co-Prosperity Sphere.
3. Japan refused to leave Mainland China unless it kept its puppet state of Manchukuo.^[22]

In its final proposal on November 20, Japan offered to withdraw its forces from southern Indochina and not to launch any attacks in Southeast Asia if the U.S., Britain, and the Netherlands ceased aiding China and lifted their sanctions against Japan.^[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.

Breaking off negotiations

Part of the Japanese plan for the attack included breaking off negotiations with the United States 30 minutes before the attack began. Diplomats from the Japanese embassy in Washington, D.C., including the Japanese ambassador, Admiral Kichisaburō Nomura and Special Representative Saburō Kurusu, had been conducting extended talks with the U.S. State Department regarding reactions to the Japanese move into French Indochina in the summer.

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

The United States had decrypted the 14th part well before the Japanese did so, and long before, embassy staff had composed a clean typed copy. 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]}.

Nomura asked for an appointment to see Hull at 1:00 pm but later asked it be postponed to 1:45 as Nomura was not quite ready. Nomura and Kurusu arrived at 2:05 pm and were received by Hull at 2:20. Nomura apologized for the delay in presenting the message. After Hull had read several pages, he asked Nomura whether the document was presented under instructions of the Japanese government. Nomura replied that it was. After reading the full document, Hull turned to the ambassador and said:

I must say that in all my conversations with you... during the last nine months I have never uttered one word of untruth. This is borne out absolutely by the record. In all my fifty years of public service I have never seen a document that was more crowded with infamous falsehoods and distortions--infamous falsehoods and distortions on a scale so huge that I never imagined until today that any Government on this planet was capable of uttering them.^[23]

Japanese records, which were admitted into evidence during congressional hearings on the attack after the war, established that Japan had not even written a declaration of war until it had news of the successful attack. The two-line declaration was finally delivered to U.S. Ambassador Joseph Grew in Tokyo about ten hours after the completion of the attack. Grew was allowed to transmit it to the United States, where it was received late Monday afternoon (Washington time).

War

In July 1941, IJN headquarters informed Emperor Hirohito its reserve

On October 16, 1941, Konoe resigned and proposed Prince Naruhiko Higashikuni, who was also the choice of the army and navy, as his successor. 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.^[25] Prince Naruhiko Higashikuni became prime minister on 17 August 1945, after the surrender of Japan.

On November 3, 1941, Nagano presented a complete plan for the attack on Pearl Harbor to Hirohito.^[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.^[27] Over the following weeks, Tōjō's military regime offered a final deal to the United States. It offered to leave only Indochina in return for large American economic aid.^{[citation needed]} On November 26, the so-called Hull Memorandum (or Hull Note) rejected the offer and stated that in addition to leaving Indochina, the Japanese must leave China and agree to an Open Door Policy in the Far East.^[28]

On 30 November 1941,

On February 3, 1940, Yamamoto briefed Captain Kanji Ogawa of Naval Intelligence on the potential attack plan and asked him to start intelligence gathering on Pearl Harbor. Ogawa already had spies in Hawaii, including Japanese Consular officials with an intelligence remit, and he arranged for help from a German already living in Hawaii who was an Abwehr agent. None had been providing much militarily useful information. He planned to add the 29-year-old Ensign Takeo Yoshikawa. By the spring of 1941, Yamamoto officially requested additional Hawaiian intelligence, and Yoshikawa boarded the liner Nitta-maru at Yokohama. He had grown his hair longer than military length and assumed the cover name Tadashi Morimura.^[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. He visited Pearl Harbor frequently and sketched the harbor and location of ships from the crest of a hill. Once, he gained access to

In June 1941, German and Italian consulates were closed, and there were suggestions that those of Japan should be closed, as well. They were not because they continued to provide valuable information (via MAGIC), and neither Roosevelt nor Hull wanted trouble in the Pacific.^[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.^[33]

Planning

Expecting war and seeing an opportunity in the forward basing of the U.S. Pacific Fleet in Hawaii, the Japanese began planning in early 1941 for an attack on Pearl Harbor. 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. The plans for the Pearl Harbor attack arose out of the Japanese expectation the U.S. would be inevitably drawn into war after a Japanese attack against Malaya and Singapore.^[34]

The intent of a preventive strike on Pearl Harbor was to neutralize American naval power in the Pacific and to remove it from influencing operations against American, British, and Dutch colonies. Successful attacks on colonies were judged to depend on successfully dealing with the Pacific Fleet. Planning

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. The delegation returned to Japan with information about the shallow-running torpedoes Cunningham's engineers had devised.^{[citation needed]}

Japanese strategists were undoubtedly influenced by Admiral

In a letter dated January 7, 1941, Yamamoto finally delivered a rough outline of his plan to

Although attacking the U.S. Pacific Fleet anchorage would achieve surprise, it also carried two distinct disadvantages. The targeted ships would be sunk or damaged in very shallow water and so they could quite likely be salvaged and possibly returned to duty (as six of the eight battleships eventually were). Also, most of the crews would survive the attack since many would be on shore leave or would be rescued from the harbor afterward. Despite those concerns, Yamamoto and Genda pressed ahead.

By April 1941, the Pearl Harbor plan became known as Operation Z, after the famous Z signal that was given by Admiral Tōgō at Tsushima. Over the summer, pilots trained in earnest near

At several stages during 1941, Japan's military leaders discussed the possibility of launching an invasion to seize the Hawaiian Islands to provide Japan with a strategic base to shield its new empire, deny the United States any bases beyond the West Coast and further isolate Australia and New Zealand.

Genda, who saw Hawaii as vital for American operations against Japan after war began, believed that Japan must follow any attack on Pearl Harbor with an invasion of Hawaii or risk losing the war. He viewed Hawaii as a base to threaten the West Coast of North America and perhaps as a negotiating tool for ending the war. He believed that after a successful air attack, 10,000-15,000 men could capture Hawaii, and he saw the operation as a precursor or an alternative to a

• Japan's ground forces, logistics, and resources were already fully committed not only to the Second Sino-Japanese War but also for offensives in Southeast Asia, which were planned to occur almost simultaneously with the Pearl Harbor attack.
• The Imperial Japanese Army (IJA) insisted it needed to focus on operations in China and Southeast Asia and so refused to provide substantial support elsewhere. Because of a lack of co-operation between the services, the IJN never discussed the Hawaiian invasion proposal with the IJA.^[40][g]
• Most of the senior officers of the Combined Fleet, particularly Admiral Nagano, believed an invasion of Hawaii was too risky.^[h][40]

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. Japanese planners knew that Hawaii, with its strategic location in the Central Pacific, would serve as a critical base from which the U.S. could extend its military power against Japan. However, the confidence of Japan's leaders that the conflict would be over quickly and that the U.S. would choose to negotiate a compromise, rather than fight a long bloody war, overrode that concern.^{[i][41][42][43]}

Watanabe's superior, Captain Kameto Kuroshima, who believed the invasion plan unrealistic, would later call his rejection of it the "biggest mistake" of his life.^[40]

Strike force

On November 26, 1941, the day that the

Execute order

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.^[47] [The Kido Butai will] proceed to the Hawaiian Area with utmost secrecy and, at the outbreak of the war, will launch a resolute surprise attack on and deal a fatal blow to the enemy fleet in the Hawaiian Area. The initial air attack is scheduled at 0330 hours, X Day.^[47]

Upon completion, the force was to return to Japan, re-equip, and redeploy for "Second Phase Operations."

Finally, Order Number 9, issued on 1 December 1941 by Nagano, told Yamamoto to crush hostile naval and air forces in Asia; the Pacific and Hawaii; seize the main U.S., British, and Dutch bases in East Asia promptly; and "capture and secure the key areas of the southern regions."^[47]

On the home leg, the force was ordered to be alert for tracking and counterattacks by the Americans and to return to the friendly base in the Marshall Islands, rather than the Home Islands.^[48]

Lack of preparation

In 1924, General

There was also confusion about the Army's readiness status as Short had changed local alert level designations without clearly informing Washington. Most of the Army's mobile anti-aircraft guns were secured, with ammunition locked down in armories. To avoid upsetting property owners and in keeping with Washington's admonition not to alarm civil populations (such as in the late November war warning messages from the Navy and War Departments), guns were not dispersed around Pearl Harbor (on private property)^[citation needed]. 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.

• Pearl Harbor advance-knowledge conspiracy theory

Notes