On the morning of December 7, 1941, planes of the Imperial Japanese Navy carried out a surprise assault on the American Navy base and Army air field at Pearl Harbor, Oahu, Hawaii. This attack has been called the Bombing of Pearl Harbor and the Battle of Pearl Harbor but, most commonly, the Attack on Pearl Harbor or simply Pearl Harbor.

The Japanese planes bombed all the US military air bases on the island (the biggest was the U.S. Army air base at Hickam Field), and the ships anchored at Pearl, including "Battleship Row". The battleship USS Arizona blew up, turned over, and sank with a loss of over 1,100 men, nearly half of the American dead. It became and remains a memorial to those lost that day. Seven other battleships and twelve other ships were sunk or damaged, 188 aircraft were destroyed, and 2,403 Americans lost their lives.

On November 26 a fleet of six aircraft carriers commanded by Japanese Vice Admiral Chuichi Nagumo left Hitokapu Bay headed for Pearl Harbor under strict radio silence.

The Japanese aircraft carriers were: Akagi, Hiryu, Kaga, Shokaku, Soryu, Zuikaku. Together they had a total of 441 planes, including fighters, torpedo-bombers, dive-bombers, and fighter-bombers. The planes attacked in two waves, and Admiral Nagumo decided to forego a third attack in favor of withdrawing. Of these, 55 were lost during the battle.

The USS Arizona burning after the Japanese attack on Pearl Harbor

Table of contents
1 Strategy
2 Historical significance
3 Aftermath
4 Advance Knowledge Debate
5 Further reading
6 External Links


The purpose of the attack on Pearl Harbor was to neutralize American naval power in the Pacific. Japan had been embroiled in a war with China for some years and had seized Manchuria some years before. Planning had begun for a Pearl Harbor attack in support of further military advances in January of 1941, and training was underway by mid-year after the project was finally judged achievable after some Imperial Navy infighting.


The invasion of southern Indo-China beginning in mid-1941 provoked the major powers in the area into action, more than the diplomatic protest notes which had been the usual for nearly a decade: the United States, with Britain and the Dutch colonial government, imposed an embargo of strategic materials to Japan in July. This "threat" to the Japanese economy (and military supplies) was intended to force them to reconsider the move into Indo-China and perhaps even to negotiate. It seems instead to have increased the Japanese military's commitment to a conquer and exploit approach toward areas with the resources now endangered by the boycott. With limited oil production and quite limited refined fuel reserves, the Japanese leadership took the embargo as the stimulus to activate plans to seize supplies of strategic material in Asia, particularly southeast Asia. They could not expect the United States to remain unmoved by their plans when activated; it was this expectation which had led Admiral Yamamoto to consider ways to pre-emptively neutralize American power in the Pacific. His idea of an attack on the naval base at Pearl Harbor was one tactic to achieve this strategic goal.

Immediate outcome

In terms of its strategic objectives the attack on Pearl Harbor was, in the short to medium term, a spectacular success which eclipsed the wildest dreams of its planners and has few parallels in the military history of any era. For the next six months, the United States Navy was unable to play any significant role in the Pacific War. With the U.S.
Pacific Fleet essentially out of the picture, Japan was free to conquer southeast Asia, the entire southwest Pacific and extend its reach far into the Indian Ocean.

Longer-term effects

In the longer term, however, the Pearl Harbor attack was an unmitigated strategic disaster for Japan. Indeed Yamamoto Isoroku, whose idea the Pearl Harbor attack was, had predicted that even a successful attack on the U.S. Fleet would not win a Nipponese-American war. In the first place, one of the main Japanese objectives was the three American aircraft carriers stationed in the Pacific, but these had sortied from Pearl Harbor a few days before the attack and escaped unharmed. Putting most of the U.S. battleships out of commission, was widely regarded--by both Navies--as a tremendous success for the Japanese. The elimination of the battleships left the U.S. Navy with no choice but to put its faith in aircraft carriers and submarines, these being most of what was left--and these were the tools with which the U.S. Navy halted and then reversed the Japanese advance. The loss of the battleships didn't turn out to be as important as most everyone thought before (in Japan) and just after (in Japan and the U.S.) the attack.

Most significantly of all, the Pearl Harbor attack galvanized a divided nation into action as little else could have done. Overnight, it made the whole of America utterly determined to defeat Japan, and it probably made possible the unconditional surrender position taken by the Allied Powers. Some historians believe that Japan was doomed to defeat by the attack on Pearl Harbor itself, regardless of whether the fuel depots and machine shops were destroyed or if the carriers had been in port and sunk.

U.S. response

On December 8, 1941, the U.S. Congress declared war on Japan with only one dissenting vote. Franklin D. Roosevelt both proposed and signed the declaration of war shortly afterward, calling the previous day "a date which will live in infamy." The U.S. Government continued and intensified its military mobilization, and started to convert to a war economy.

A related question is why Nazi Germany declared war on the United States December 11, 1941 immediately following the Japanese attack. Hitler was under no obligation to do so under the terms of the Axis Pact, but did anyway. This doubly outraged the American public and allowed the United States to greatly step up its support of the United Kingdom, which delayed for some time a full U.S. response to the setback in the Pacific.

Historical significance

This battle, like the Battle of Lexington and Concord, had history-altering consequences. It only had a small military impact due to the failure of the Japanese Navy to sink U.S. aircraft carriers, but it firmly drew the United States into World War II leading to the defeat of the Axis powers worldwide. The Allied victory in this war and US emergence as a dominant world power has shaped international politics ever since.


Despite the perception of this battle as a devastating blow to America, only five ships were permanently lost to the Navy. These were the battleships USS Arizona, USS Oklahoma, the old target ship USS Utah, and the destroyers USS Cassin and USS Downes; nevertheless, much usable material was salvaged from them, including the two aft main turrets from the Arizona. Four ships sunk during the attack were later raised and returned to duty, including the battleships USS California, USS West Virginia and USS Nevada. Of the 22 Japanese ships that took part in the attack, only one survived the war.

There are many who say that the Japanese would have been wise to have attacked with a third strike to destroy the oil storage facilities, machine shops and dry docks at Pearl Harbor. Destruction of these facilities would have greatly increased the U.S. Navy's difficulties as the nearest Fleet facilities would have been several thousand miles east of Hawaii on the West Coast of the States. Admiral Nagumo declined to order a third strike for several reasons.

  • First, losses during the second strike had been more significant than during the first, a third strike could have been expected to suffer still worse losses.
  • Second, the first two strikes had essentially used all the previously prepped aircraft available, so a third strike would have taken some time to prepare, allowing the Americans time to, perhaps, find and attack Nagumo's force. The location of the American carriers was and remained unknown to Nagumo.
  • Third, the Japanese planes had not practiced attack against the Pearl Harbor shore facilities and organizing such an attack would have taken still more time, though several of the strike leaders urged a third strike anyway.
  • Fourth, the fuel situation did not permit remaining on station north of Pearl Harbor much longer. The Japanese were acting at the limit of their logistical ability to support the strike on Pearl Harbor. To remain in those waters for much longer would have risked running unacceptably low on fuel.
  • Fifth, the timing of a third strike would have been such that aircraft would probably have returned to their carriers after dark. Night operations from aircraft carriers were in their infancy in 1941, and neither the Japanese nor anyone else had developed reliable technique and doctrine.
  • Sixth, the second strike had essentially completed the entire mission, neutralization of the American Pacific Fleet.
  • Finally, there was the simple danger of remaining near one place for too long. The Japanese were very fortunate to have escaped detection during their voyage from the Inland Sea to Hawaii. The longer they remained off Hawaii, they more danger they were in, e.g., from a lucky U.S. Navy submarine, or from the absent American carriers.

Despite the debacle, there were American military personnel who served with distinction in the incident. An ensign got his ship underway during the attack. Probably the most famous is Doris Miller, an African-American sailor who went beyond the call of duty during the attack when he took control of an unattended machine gun and used it in defense of the base. He was awarded the Navy Cross.

The attack has been depicted, more (or less) accurately, numerous times on film with the best known examples such as below:

The surprise attack on Pearl Harbor and the resulting state of war between Japan and the United States were factors in the later Japanese internment in the western United States. Another important factor were the racial views of General John DeWitt, commander of the West Coast Defense District. He claimed existence of evidence of sabotage and espionage intentions among the Japanese and Japanese descended in support of his recommendation to President Roosevelt that those of Japanese descent be interned. He had no such evidence.

In 1991, it was rumored that Japan was going to release an official apology to the United States for the attack. The apology did not come in the form many expected, however. The Japanese Foreign Ministry released a statement that said Japan had intended to release a formal declaration of war to the U.S. at 1 P.M., twenty-five minutes before the attacks at Pearl Harbor were scheduled to begin. However, due to various delays, the Japanese ambassador was unable to release the declaration until well after the attacks had begun. For this, the Japanese government apologized.

Advance Knowledge Debate

There has been considerable debate ever since December 8, 1941, as to how and why the United States had been caught unaware, and how much and when American officials knew of Japanese plans and related topics. Some have argued that various parties (in some theories Roosevelt and/or other American officials, in others Churchill and the British, in still others all of the above) knew of the attack in advance and may even have let it happen in order to propel America into war.

Examination of information released since the War, has revealed that there was considerable intelligence information available to US, and other, officials. It was the failure to process and use this information effectively that has led some to invoke conspiracy theories rather than a more boring mix of mistakes and incompetence. The US government had six official enquires into the attack - The Roberts Commission (1941), the Hart Inquiry (1944), the Army Pearl Harbor Board (1944), the Naval Court of Inquiry (1944), the Congressional Inquiry (1945-46) and the top-secret inquiry by Secretary Stimson authorized by Congress and carried out by Henry Clausen (the Clausen Inquiry (1945)).

One factor making an attack against Pearl Harbor 'unthinkable' was the shallow anchorage at Pearl Harbour. Such depths were generally considered to make effective torpedo attack impossible. But the British had proved that modified torpedoes could manage in shallow water during their attack on the Italian Navy at Taranto on November 11, 1940. The US Navy overlooked the significance of this new development. The Japanese had independently developed shallow water torpedo modifications during the spring and summer of 1941, during the planning and training for the raid.

US signals intelligence in 1941 was both impressively advanced and uneven. The US had the capability in the period just before December 1941 to read several Japanese codes and ciphers. MI8 had been shut-down in 1929 by Henry Stimson (Hoover's newly appointed Secretary of State), but cryptanalytic work continued in two separate efforts by the Army's Signal Intelligence Service (SIS) and the Office of Naval Intelligence's (ONI) crypto group, OP-20-G. By 1941, those groups had broken several Japanese cyphers (mostly diplomatic, eg 'PA-K2' and the 'Purple Code') and had made some progress against some naval codes/cyphers (eg, the pre-December version of JN-25). In fact, the break of the Purple cypher was a considerable cryptographic triumph and proved quite useful later in the War. It was the highest security Japanese Foreign Office cypher. Unfortunately, the two groups generally competed rather than cooperated, and distribution of intelligence from the military to US civilian policy-level officials was poorly done, and in a way that prevented any of its receipients from developing a 'larger sense' of the meaning of the decrypts.

Japanese intelligence efforts against Pearl Harbor included at least two German Abwehr agents, one of them a sleeper living in Hawaii with his family; he and they were essentially incompetent. The other, Dusko Popov, was quite effective in Abwehr eyes, but unknown to them was a double agent whose chief loyalty was to the British. He worked for the XX Committee of MI5. In August 1941 he was tasked by the Abwehr with some specific questions about Pearl (see John Masterman's book on the Double Cross operation for the text of the questionnaire), but the FBI seems to have evaluated the effort as of negligible importance. There has been no report that its existence, or Popov's availability as a double agent, was even passed on to US military intelligence or to civilian policy officials. J. Edgar Hoover dismissed Popov's importance noting that his British codename, Tricyle, was connected with his sexual tastes. (?!) In any case, he was not allowed to continue on to Hawaii.

Throughout 1941, the US, Britain, and Holland collected a considerable range of evidence suggesting that Japan was heading for war against someone new. But the Japanese attack on the US in December was essentially a side operation to the main Japanese thrust south against Malaya and the Philippines -- many times the resources, especially Imperial Army resources, were devoted to these attacks as compared to Pearl. Many in the Japanese military (both Army and Navy) had disagreed with Yamamoto's plan when it was first proposed in early 1941, and remained reluctant through the Imperial Conferences in September and November which first approved it as policy and then authorized the attack. The Japanese focus on South-East Asia was accurately reflected in US intelligence assessments; there were warnings of attacks against Thailand (the Kra Peninsula), against Malaya, against French Indochina, against the Dutch East Indies, even one against Russia. There was even a specific claim of a plan for an attack on Pearl Harbor from the Peruvian Ambassador to Japan in early 1941. Since even Yamamoto had not yet then even decided to argue for an attack Pearl Harbor, discounting US Ambassador Grew's report about it to Washington in early 1941 was quite sensible. There has been no report of a serious advance conviction by anyone in US or UK military intelligence or among US civilian policy officials that Pearl Harbor or the US West Coast would be attacked. The so-called "Winds Code" announcing the outbreak of hostilies remains a curious and confused episode, demonstrating the uncertainty of intelligence information, especially some years after the event. Nevertheless, in late November, both the US Navy and Army sent explicit war warnings to all Pacific commands. Uniquely among those Pacific commands, the local Hawaii commanders, Admiral Kimmel and General Short did little to prepare for war in their command areas. Inter-service rivalries between Kimmel and Short did not improve the situation.

As Nagumo's attacking force neared Hawaii, there is claimed by some to have been a flurry of later warnings. The SS Lurline, heading from San Francisco to Hawaii, is said to have heard and plotted radio traffic. That traffic is further said to have been from the Japanese fleet. There are problems with this. All surviving officers from Nagumo's ships claim that there was no radio traffic to have been overheard; their radio operators had been left in Japan to fake traffic for the benefit of listeners, and all radios aboard Nagumo's ships were physically locked to prevent inadvertent use. Unfortunately, the Lurline's log hasn't been found, so contemporaneous evidence of what was heard isn't available. ONI is further said to have been aware of the eastwards movement of Japanese carriers from other sources, but nothing in the way of credible evidence on this point has yet turned up.

Closer to the moment of the attack, the attacking planes were detected and tracked by an Army radar installation being used for training, mini-subs were sighted and attacked ourside Pearl Harbor and at least one was sunk -- all before the planes came within bombing range.

Japanese consular officials in Hawaii, including spy and Naval officer Takeo Yoshikawa, had been sending information about conditions in Hawaii, and in Pearl Harbor, for months. Some of this information was hand delivered to intelligence officers aboard Japanese vessels calling in Hawaii, but some of it was transmitted back to Tokyo. Many of these messages overheard and decrypted. None explicitly stated anything about an attack on Pearl except a message of 6 December, which was not decrypted until after the 7th. No cable traffic was intercepted in Hawaii until after David Sarnoff of RCA agreed to assist in a visit to Hawaii immediately before the 7th; such interception was illegal under US law. Locally, Naval Intelligence had been tapping telephones at the Japanese Consulate before the 7th, and overheard a most peculiar discussion of flowers in a call to Tokyo (the significance of which is still opaque), but the Navy's tap was discovered and was disconnected by the Navy in the first week of December. They didn't tell the local FBI about either the tap or its removal; the local FBI agent in charge later claimed he would have had installed one of his own if he'd known the Navy's had been disconnected.

Further reading

Further reading - Alternative Theories

  • John Toland, Infamy: Pearl Harbor and Its Aftermath (Berkeley, reissue edition 1991) is an account of the various investigations of the US failure to be prepared at Pearl. He claims that Roosevelt had advance knowledge of the attack, which he deliberately did not use to warn the commanders at Pearl. Note that some of Toland's sources have said that his interpretation of their experiences is incorrect.
  • James Rusbridger and Eric Nave, Betrayal at Pearl Harbour: How Churchill Lured Roosevelt into WWII (Summit, 1991) which posits that while the Americans couldn't read the Japanese naval code, the British could, and Churchill deliberately withheld warning because the UK needed U.S. help. Nave was an Australian cryptographer whose diaries were used in writing this book. A check against them has made clear that some of the charges Rusbridger makes here are unsupported by Nave's diaries of the time.
  • Robert Stinnett, Day Of Deceit: The Truth About FDR and Pearl Harbor (Free Press, 2001) is a recent examination which begins with the conviction that Roosevelt deliberately steered Japan into war with America, and ends with the same conclusion. Stinnett's understanding of cryptography is quite limited and his conclusions regarding the cryptographic evidence are accordingly unreliable. He also sees a great deal of meaning in short analysis memos which support his thesis and less meaning in other information that does not. A distinctly limited account.

External Links

Alternative Theories