Edited by Gerald Boerner




On the eve of that memorial day so long ago, we examine some of the reasons for the Japanese attack on Pearl Harbor that Sunday morning of 1941. The U.S. Navy was seemingly unprepared for the attack. The negotiations with the Japanese Embassy in Washington, D.C., had not been completed at the time of the attack, and there was a seemingly sequence of miscommunications between the military leaders in D.C. and Hawaii. All-in-all, The U.S. was unprepared for an air attack at Pearl Harbor.


The Japanese, on the other hand, were driven by both their territorial ambitions and their quest for raw resources. These two drives prompted the military leaders to plan to attack on the Navy’s Pacific fleet in Pearl Harbor. Spies were in place in Honolulu. A task force with four carriers were making their way to the islands. All was set for the attack on the morning of December 7th.

But beyond these two obvious reasons, we find that the general culture of militarism in Japan also placed an important role. The leaders of the Japanese government were tied closely to this warrior tradition. This same mindset of militarism would later spawn the Kamikaze pilots who were willing to give their lives in the defense of their homeland.

On the American side, the ambivalent tradition of isolationism within the American Congress resulted in substantial unpreparedness. Communication was misunderstood, instruction to guard the harbor and land bases in the tropical paradise that was the Hawaiian Islands resulted in a generalized fear of spies among the Japanese Americans living in Honolulu resulted in the ships and planes being grouped together in such a manner as to facilitate the mass destruction that resulted from the attack. The one bright spot was the fact that the aircraft carriers being out to sea rather than in the harbor that fateful morning.  

But enough of these preliminaries. Let’s begin our exploration of these critical event in our nation’s history…  GLB

These Introductory Comments are copyrighted:
Copyright©2011 — Gerald Boerner — All Rights Reserved

[ 4364 Words ]


Quotations Related to Pearl Harbor:


“I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve.”
— Isoroku Yamamoto

“After Barbarossa and Pearl Harbor, the war tide slowly turned against the Axis.”
— Alexander Dubcek

“As costly as it was in the lives of our men and women in uniform, in military assets, and in esteem and pride, Pearl Harbor was a watershed moment for America.”
— Joe Baca

“As costly as it was in the lives of our men and women in uniform, in military assets, and in esteem and pride, Pearl Harbor was a watershed moment for America.”
— Joe Baca

“But in 1941, on December 8th, after the Japanese attacked Pearl Harbor, my mother bought a radio and we listened to the war news. We’d not had a radio up to that time. I was born in 1934, so I was seven years of age.”
— Sam Donaldson

“Can any of us even imagine, after Pearl Harbor, President Roosevelt suggesting we negotiate a resolution or that we could simply prosecute those involved? Of course it is unimaginable. We are right to be in the Middle East, and we are right to treat this as the war it is.”
— Marsha Blackburn

“But in 1941, on December 8th, after the Japanese attacked Pearl Harbor, my mother bought a radio and we listened to the war news. We’d not had a radio up to that time. I was born in 1934, so I was seven years of age.”
— Sam Donaldson

“Japanese naval officers in dress whites are frequent guests at Pearl Harbor’s officers’ mess and are very polite. They always were. Except, of course, for that little interval there between 1941 and 1945.”
— William Manchester


Pearl Harbor: Part 1, Background of the Conflict…


Pearl_Harbor_aerialA series of events led to the attack on Pearl Harbor. War between Japan and the United States had been a possibility that each nation’s military forces planned for since the 1920s, though real tension did not begin until the 1931 invasion of Manchuria by Japan. Over the next decade, Japan expanded slowly into China, leading to all out war between the two in 1937. In 1940 Japan invaded French Indochina in an effort to embargo all imports into China, including war supplies purchased from the U.S. This move prompted the United States to embargo all oil exports, leading the Imperial Japanese Navy to estimate that it had less than two years of bunker oil remaining and to support the existing plans to seize oil resources in the Dutch East Indies. 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 that Japan envisioned in the Pacific.

The Philippine islands, at that time an American territory, were also a Japanese target. The Japanese military concluded that an invasion of the Philippines would provoke an American military response. Rather than seize and fortify the islands, and wait for the inevitable US counterattack, Japan’s military leaders instead decided on the pre-emptive Pearl Harbor attack, which they assumed would negate the American forces needed for the liberation and reconquest of the islands.

Planning for the attack had begun in very early 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 fall. 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 final approval by Emperor Hirohito the order to attack was issued at the beginning of December.


Franklin Delano Roosevelt – Pearl Harbor Address…





Tensions among Japan, on one hand, and the prominent Western countries (the United States, France, Britain, and the Netherlands), on the other, increased significantly at the beginning of the increasingly militaristic Showa era, as Japanese nationalists and military leaders exerted increasing influence over government policy, adopting creation of a Greater East Asia Co-Prosperity Sphere as part of Japan’s alleged "divine right" to unify Asia under Emperor Showa’s rule, threatening already-established American, French, British, and Dutch colonies in Asia.

Hirohito_wartime Emperor Shōwa (Hirohito)

Over the course of the 1930s, Japan’s increasingly expansionist policies brought her into renewed conflict with her neighbors, Russia and China (Japan had fought the First Sino-Japanese War with China in 1894-95 and the Russo-Japanese War with Russia in 1904-05; Japan’s imperialist ambitions had a hand in precipitating both conflicts). 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.

On January 15, 1936, Japan withdrew from the Second London Naval Disarmament Conference because the United States and Great Britain refused to grant the Imperial Japanese Navy (IJN) parity with their navies. A second full-scale war between Japan and China began with the Marco Polo Bridge Incident in July 1937, and Japanese atrocities during the war, such as the Rape of Nanking, served to further complicate relations with the rest of the world, particularly the U.S.

The 1937 Japanese attack on China was condemned by the U.S. and by several members of the League of Nations, particularly Britain, France, Australia, and the Netherlands. These states had economic and territorial interests, or formal colonies, in East and Southeast Asia, and had become increasingly alarmed at Japan’s military power and willingness to use it, which they saw as threats to their control in Asia. In July 1939, the U.S. terminated its 1911 commercial treaty with the Japanese. These efforts, however, failed to deter Japan from continuing the war in China or from signing the Tripartite Pact in 1940 with Nazi Germany and Fascist Italy, officially forming the Axis Powers.

On October 8, 1940, Admiral James O. Richardson, commander of the Pacific Fleet, had a confrontation with President Roosevelt. Richardson repeated what he had said in his letter to Chief of Naval Operations Admiral Harold R. Stark and his memo to Secretary of the Navy Frank Knox – that Pearl Harbor was the wrong place for his ships. Roosevelt said he thought that having the fleet in Hawaii was a "restraining influence" on Japan. Richardson asked the president whether the United States was going to war. "He replied," in Richardson’s account, "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 the Japanese couldn’t always avoid making mistakes, the president said. "Sooner or later they would make a mistake and we would enter the war."

Japanese Military Buildup

The Tripartite Pact, war with China, increasing militarization, and Japan’s withdrawal from the League of Nations eventually led the U.S. to embargo scrap metal and gasoline shipments to Japan and to constrain its foreign policy actions and close the Panama Canal to Japanese shipping. In 1940, Japan moved into northern Indochina. The U.S. responded by freezing Japan’s assets in the U.S. and embargoing all oil exports to Japan. Oil was Japan’s most crucial imported resource; more than 80 percent of Japan’s oil imports at the time came from the United States To secure oil supplies, and other resources, Japanese planners had long been looking south, especially the Dutch East Indies. The Navy was certain any attempt to seize this region would bring the U.S. into the war and was reluctant to agree with other factions’ plans for invasion. The complete US oil embargo changed to the Naval view to support of expansion toward support for an invasion of the Dutch East Indies and seizure of its oil fields. In August 1941, Japanese Prime Minister Fumimaro Konoe proposed a summit with President Roosevelt to discuss differences. Roosevelt replied Japan must leave China before a summit meeting could be held.

Tojo2Prime Minister of Japan Hideki Tojo

In July 1941, the IJN headquarters informed Hirohito that its reserve bunker oil would be exhausted within two years if a new source was not found. On September 6, 1941, at the second Imperial Conference concerning attacks on the Western colonies in Asia and Hawaii, Japanese leaders met to consider the attack plans prepared by Imperial General Headquarters, one day after the emperor had reprimanded General Hajime Sugiyama, the Chief of the Imperial Japanese Army (IJA) General Staff, about the lack of success in China, and the speculated low chances of victory against the United States, British Empire, and their allies.

Prime Minister Konoe argued for more negotiations and possible concessions to avert war. However, military leaders like Sugiyama, Minister of War General Hideki Tojo, and Chief of the IJN General Staff Admiral Osami Nagano asserted that time had run out and that additional negotiations would be pointless. They urged swift military actions against all American and European colonies in Southeast Asia and Hawaii. Tojo opined yielding to the American demand to withdraw troops would wipe out all the fruits of the Second Sino-Japanese War, depress Army morale, endanger Manchukuo, and jeopardize control of Korea; hence, doing nothing was the same as defeat and a loss of face.


Prelude to Battle

Intelligence Gathering

On February 3, 1940, Yamamoto briefed Captain Kanji Ogawa of Naval Intelligence on the potential attack plan, asking 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 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.

YoshikawaEnsign Takeo Yoshikawa, a spy in Pearl
Harbor for Imperial Japan.

Yoshikawa began gathering intelligence in earnest by taking auto trips around the main islands, and toured Oahu in a small plane, posing as a tourist. He visited Pearl Harbor frequently, sketching the harbor and location of ships from the crest of a hill. Once, he gained access to Hickam Field in a taxi, memorizing the number of visible planes, pilots, hangars, barracks and soldiers. He was also able to discover that Sunday was the day of the week on which the largest number of ships were likely to be in harbor, that PBY patrol planes went out every morning and evening, and that there was an antisubmarine net in the mouth of the harbor. 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.

In June 1941, German and Italian consulates were closed, and there were suggestions Japan’s should be closed, as well. They were not, because they continued to provide valuable information (via MAGIC) and neither President Roosevelt nor Secretary Hull wanted trouble in the Pacific. 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, was no longer available.


Expecting war, and seeing an opportunity in the forward basing of the US Pacific Fleet at 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 Pearl Harbor attack planning arose out of the Japanese expectation the U.S. would be inevitably drawn into the war after a Japanese attack against Malaya and Singapore.

Isoroku_YamamotoCommander-in-Chief of the Combined Fleet
Fleet Admiral Isoroku Yamamoto

The intent of a preemptive strike on Pearl Harbor was to neutralize American naval power in the Pacific, thus removing it from influencing operations against American, British, and Dutch colonies to the south. Successful attacks on colonies were judged to depend on successfully dealing with the American Pacific Fleet. Planning had long anticipated that a battle between the two Fleets would happen in Japanese home waters after the US Fleet traveled across the Pacific, under attack by submarines and other forces all the way. The US Fleet would be defeated in a climactic battle, just as had the Russian Fleet in 1905. A surprise attack posed a twofold difficulty compared to long standing expectations. First, the US Pacific Fleet was a formidable force, and would not be easy to defeat or to surprise. Second, for aerial attack, Pearl Harbor’s shallow waters made using conventional air-dropped torpedoes ineffective. On the other hand, Hawaii’s isolation 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 Operation Judgment, in which 21 obsolete Fairey Swordfish disabled half the Regia Marina. 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, thus giving Japan the time necessary 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.

Japanese strategists were undoubtedly influenced by Admiral Togo’s surprise attack on the Russian Pacific Fleet at Port Arthur in 1905, and may have been influenced by U.S. Admiral Harry Yarnell’s performance in the 1932 joint Army-Navy exercises, which simulated an invasion of Hawaii. Yarnell, as commander of the attacking force, placed his carriers northwest of Oahu and simulated an air attack. The exercise’s umpires noted Yarnell’s aircraft were able to inflict serious "damage" on the defenders, who for 24 hours after the attack were unable to locate his force.

Yamamoto’s emphasis on destroying the American battleships was in keeping with the Mahanian doctrine shared by all major navies during this period, including the U.S. Navy and Royal Navy.

Minoru_GendaPlanner Commander Minoru Genda stressed
surprise would be critical.

In a letter dated January 7, 1941 Yamamoto finally delivered a rough outline of his plan to Koshiro Oikawa, then 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, this time directed at Takijiro Onishi—chief of staff of the Eleventh Air Fleet—Yamamoto requested Onishi study the technical feasibility of an attack against the American base. After consulting first with Kosei Maeda, an expert on aerial torpedo warfare, and being told the harbor’s shallow waters rendered such an attack almost impossible, Onsihi summoned Commander Minoru Genda. After studying the original proposal put forth by Yamamoto, Genda agreed: "the plan is difficult but not impossible". During the following weeks, Genda expanded Yamamoto’s original plan, highlighting the importance of it being carried out early in the morning and in total secrecy, employing an aircraft carrier force and several different types of bombing.

Although attacking the US Pacific Fleet while it was at anchor in Pearl Harbor would achieve surprise, it also carried two distinct disadvantages: The targeted ships would be sunk or damaged in very shallow water, meaning that it would quite likely they could be salvaged and possibly returned to duty (as six of the eight battleships eventually were); and most of the crews would survive the attack, since many would be on shore leave or would be rescued from the harbor afterward. Despite these concerns, Yamamoto and Genda pressed ahead.

By April 1941, the Pearl Harbor plan became known as Operation Z, after the famous Z signal given by Admiral Tōgō at Tsushima. Over the summer, pilots trained in earnest near Kagoshima City on the Japanese island of Kyūshū. Genda had chosen it because its geography and infrastructure presented most of the same problems bombers would face at Pearl Harbor. In training, each crew flew over the 5000-foot (1500 m) mountain behind Kagoshima, dove down into the city, dodging buildings and smokestacks before dropping to an altitude of 25 feet (7 m) at the piers. Bombardiers released torpedoes at a breakwater some 300 yards (270 m) away.

Yet even skimming the water did not solve the problem of torpedoes bottoming in the shallow waters of Pearl Harbor. Japanese weapons engineers created and tested modifications allowing successful shallow water drops. The effort resulted in a heavily modified version of the Type 91 torpedo which inflicted most of the ship damage during the attack. Japanese weapons technicians also produced special armor-piercing bombs by fitting fins and release shackles to 14 and 16 inch (356 and 406 mm) naval shells. These were able to penetrate the lightly armored decks of the old battleships.

The Lack of Preparation By the United States

U.S. civil and military intelligence had, amongst them, good information suggesting additional Japanese aggression throughout the summer and fall before the attack. At the time, no reports specifically indicated an attack against Pearl Harbor. Public press reports during summer and fall, including Hawaiian newspapers, contained extensive reports on the growing tension in the Pacific. Late in November, all Pacific commands, including both the Navy and Army in Hawaii, were separately and explicitly warned war with Japan was expected in the very near future, and it was preferred that Japan make the first hostile act as they were apparently preparing to do. It was felt that war would most probably start with attacks in the Far East: the Philippines, Indochina, Thailand, or the Russian Far East.

Walter_ShortLieutenant General Walter C. Short, commanding general
of the Army post at Pearl Harbor

The warnings were not specific to any area, noting only that war with Japan was expected in the near future and all commands should act accordingly. Had any of these warnings produced an active alert status in Hawaii, the attack might have been resisted more effectively, and perhaps resulted in less death and damage. On the other hand, recall of men on shore leave to the ships in harbor might have led to still more being casualties from bombs and torpedoes, or trapped in capsized ships by shut watertight doors (as the attack alert status would have required), or killed (in their obsolete aircraft) by more experienced Japanese aviators.

When the attack actually arrived, Pearl Harbor was effectively unprepared: anti-aircraft weapons not manned, most ammunition locked down, anti-submarine measures not implemented (e.g., no torpedo nets in the harbor), combat air patrol not flying, available scouting aircraft not in the air at first light, Air Corps aircraft parked wingtip to wingtip to reduce sabotage risks (not ready to fly at a moment’s warning), and so on.

By 1941, U.S. signals intelligence, through the Army’s Signal Intelligence Service and the Office of Naval Intelligence’s OP-20-G, had intercepted and decrypted considerable Japanese diplomatic and naval cipher traffic, though nothing actually carrying significant information about Japanese military plans in 1940-41. Decryption and distribution of this intelligence, including such decrypts as were available, was capricious and sporadic, some of which can be accounted for by lack of resources and manpower. At best, the information available to decision makers in Washington was fragmentary, contradictory, or poorly distributed, and was almost entirely raw, without supporting analysis. It was thus, incompletely understood. Nothing in it pointed directly to an attack at Pearl Harbor, and a lack of awareness of Imperial Navy capabilities led to a widespread underlying belief Pearl Harbor was not a possible attack target. Only one message from the Hawaiian Japanese consulate (sent on 6 December), in a low level consular cipher, included mention of an attack at Pearl; it was not decrypted until 8 December.

In 1924, General William L. Mitchell produced a 324-page report warning that future wars (including with Japan) would include a new role for aircraft against existing ships and facilities. He even discussed the possibility of an air attack on Pearl Harbor, but his warnings were ignored. Navy Secretary Knox had also appreciated the possibility of an attack at Pearl in a written analysis shortly after taking office. American commanders had been warned that tests had demonstrated shallow-water aerial torpedo attacks were possible, but no one in charge in Hawaii fully appreciated this. And a war game surprise attack against Pearl Harbor in 1932 had been judged a success and to have caused considerable damage.

Nevertheless, because it was believed Pearl Harbor had natural defenses against torpedo attack (e.g., the shallow water), the Navy did not deploy torpedo nets or baffles, which were judged to inconvenience ordinary operations. And as a result of limited numbers of long-range aircraft (including Army Air Corps bombers), reconnaissance patrols were not being made as often or as far out as required for adequate coverage against possible surprise attack; they improved considerably, with far fewer remaining planes, after the attack. The Navy had 33 PBYs in the islands, but only three on patrol at the time of the attack. Hawaii was low on the priority list for the B-17s finally becoming available for the Pacific, largely because General MacArthur in the Philippines was successfully demanding as many as could be made available to the Pacific (where they were intended as a deterrent). The British, who had contracted for them, even agreed to accept fewer to facilitate this buildup. At the time of the attack, Army and Navy were both on training status rather than operational alert.

There was also confusion about the Army’s readiness status as General 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 (e.g., in the late November war warning messages from the Navy and War Departments), guns were not dispersed around Pearl Harbor (i.e., on private property). 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.

Chester Nimitz said later, "It was God’s mercy that our fleet was in Pearl Harbor on December 7, 1941.". Nimitz believed if Kimmel had discovered the Japanese approach, he would have sortied to meet them. With the American carriers absent and Kimmel’s battleships at a severe disadvantage to the Japanese carriers, the likely result would have been the sinking of the American battleships at sea in deep water, where they would have been lost forever with tremendous casualties (as many as twenty thousand dead), instead of in Pearl Harbor, where the crews could easily be rescued, and six battleships ultimately raised.



The Pearl Harbor – Historical Background…


Pearl Harbor…



Please take time to further explore more about Pearl Harbor, National Pearl Harbor Remembrance Day, Events Leading to the Attack on Pearl Harbor, Attack on Pearl Harbor, Isoroku Yamamoto, Imperial Japanese Navy (IJN), Greater East Asia Co-Prosperity Sphere by accessing the Wikipedia articles referenced below. In most cases, the text in the body of this post has been selectively excerpted from the articles; footnotes and hyperlinks have been removed for readability…





Background information is from Wikipedia articles on:

Wikipedia: Pearl Harbor…

Wikipedia: National Pearl Harbor Remembrance Day

Wikipedia: Events Leading to the Attack on Pearl Harbor…

Wikipedia: Attack on Pearl Harbor…

Wikipedia: Isoroku Yamamoto…

Wikipedia: Imperial Japanese Navy…

Wikipedia: Greater East Asia Co-Prosperity Sphere…

Brainy Quote: Pearl Harbor Quotes…


Other Posts on related Topics:

Prof. Boerner’s Explorations: Revisiting the Archives — Pearl Harbor: Understanding the Context…

Prof. Boerner’s Explorations: Pearl Harbor: Background of the Surprise Attack…

Prof. Boerner’s Explorations: Pearl Harbor: Background of the Conflict…