According to "British Intelligence in the Second World War: Security and Counter-Intelligence", by Francis Harry Hinsley and C.A.G. Simkins, Tricycle, a British double agent, complained that the FBI ignored the "obvious warning" of the forthcoming attack on Pearl Harbor (read more below ↓).

Also, according to "Conspiracies and Secret Societies: The Complete Dossier", by Brad Steiger & Sherry Steiger, it seems that the Japanese diplomatic code had been broken by FBI and almost all messages between Tokyo and its embassy in Washington were being intercepted and understood by Washington (read more below ↓).

Therefore, as it is possible to argue, there is no longer any doubt that FBI and, perhaps, Franklin Delano Roosevelt, were aware that an attack on Pearl Harbor was developing and that it was scheduled for December 7th.

Then a terrible question arises: was the attack on the American forces at Pearl Harbor totally unexpected?

If not, why did no one alert defense forces to protect Pearl Harbor?

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  • 10
    This is a controversial question that people have written entire books about (some of them are quite good reads, actually). Although you can get a good brief answer here, if you're really into the topic, you should get a good book about it.
    – Luke_0
    Commented Aug 10, 2013 at 17:02
  • 5
    and you should not believe the conspiracy theorists... Yes, in 20-20 hindsight there were indications that the Japanese were planning a move against the US fleet. At the time however those were not recognised as such.
    – jwenting
    Commented Aug 10, 2013 at 17:30
  • 1
    There was also equally good evidence for many other possibilities, and at the time each had people who thought it was clear that their fear was the correct one. It's only afterwards that people can see how obvious the answer that turned out to be right was all along.
    – Mark Olson
    Commented Jan 4, 2019 at 20:44
  • 1
    @Santiago There was a massive Congressional investigation into the attack shortly after the war, which uncovered a lot of things. I doubt anything significant is still deeply buried after over seven decades. Commented Jan 5, 2019 at 17:21
  • 2
    Another big hole in the conspiracy theories is that, at the time, battleships were still considered to be key ships. In hindsight, sacrificing all those battleships while saving the carriers might seem militarily acceptable, if you were totally without any ethics. But it wouldn't have seemed that way at the time, although Billy Mitchell had, I believe already been rehabilitated by that time. Hasn't stopped people from peddling those theories though. One counterpoint to keep in mind though is that the Japanese did something similar to Port Arthur in 1904. Commented Jan 7, 2019 at 7:34

5 Answers 5


Indeed, Japanese diplomatic codes had been broken. But the message sent to the Japanese Embassy in Washington, intended to be delivered before the attack (but in fact delivered later) did not contain a formal declaration of war, so although Washington knew a few hours before the attack that diplomacy was coming to an end, and war was coming, they did not receive a declaration of war, and did not expect an attack. (1)

It is sometimes claimed that the US leadership should have known that Japan would attack before a declaration of war was made, but from the US standpoint Japan and the US was still in active negotiations. The last part of the message did end those negotiations, but that part had not yet been decoded when the attack happened.

In addition to that, the Japanese fleet had been travelling under complete radio silence, and had been undetected by the United States, so the US did not know that there was a fleet within attacking distance. (2)

So yes, the attack was completely unexpected. The US thought Pearl Harbor was safe, well out of the reach of the Japanese, and negotiations was still underway.

(1) John Toland, Infamy: Pearl Harbor and Its Aftermath

(2) Donald M. Goldstein, Katherine V. Dillon: The Pearl Harbor Papers

  • 3
    If you follow that link and actually read the message, absolutely right that this was not a declaration of war. All it says is "it is impossible to reach an agreement through further negotiations."
    – T.E.D.
    Commented Aug 19, 2013 at 23:03
  • @T.E.D.: However, that may be as close as the Japanese have ever come to a formal declaration of war. Commented Jan 5, 2019 at 11:52
  • @PieterGeerkens The Japanese followed the attack up with a conventional declaration of war. Commented Jan 5, 2019 at 17:22
  • @DavidThornley: Before or after Roosevelt's Day of Infamy speech? When you are already at war, a conventional declaration is not a formality but a farce. Commented Jan 5, 2019 at 17:31
  • 1
    Was it farcical for the US to declare war on Germany, then? After the Germans had done it first, and they'd been in military conflict for months?
    – Ne Mo
    Commented Jan 6, 2019 at 19:16

Although the Japanese attack was unexpected in its timing, The US Navy was well aware:
(a) that the Japanese were in the habit of attacking before a formal declaration of war; and
(b) that a surprise attack on Pearl Harbor was both possible and likely to be devastating, having itself simulated such an attack several times over the past 15 years as outlined here

Fleet Problem XIV

“The 1933 problem was designed to simulate a war in the Pacific, one initiated by carrier operations. Anticipating that Japan would attack before formally declaring war (as she had done against Russia in 1904), the scenario envisioned the sortie of the Japanese fleet eastward across the Pacific. This fleet, its sinister designation Black, had ominously prescient orders: “To inflict maximum damage on the PEARL HARBOR NAVAL BASE in order to destroy or reduce its effectiveness.”

All in all, I find it no coincidence that the Navy carriers spent as much time as possible at sea instead of Pearl, especially as tensions with Japan increased.

The claim is made below that the US Navy was unappreciative of aircraft carriers prior to Dec. 7, 1941. I submit this as evidence to the contrary (from Wkipedia, my emphasis).

In 1934, the then Chief of Bureau of Aeronautics, Navy Admiral Ernest King offered Halsey command of the aircraft carrier USS Saratoga, subject to completion of the course of an air observer. Captain Halsey elected to enroll as a cadet for the full twelve-week Naval Aviator course rather than the simpler Naval Aviation Observer program. "I thought it better to be able to fly the aircraft itself than to just sit back and be at the mercy of the pilot." Halsey earned his Naval Aviator's Wings on May 15, 1935 at the advanced age of 52, the oldest person to do so in the history of the U.S. Navy.

  • 4
    Carriers at that time were not considered very important ships by the USA navy. Japan felt differently (and were about to teach the Americans that lesson), but the USA essentially just had them because their opponents had them. So I find it unlikely in the extreme that their absence that day was a result of any clever plan on the USA's part. Hanlon's Razor should be applied here.
    – T.E.D.
    Commented Aug 10, 2013 at 19:05
  • 1
    @T.E.D.: Complete horse hockey! That may have been true of SecNav, but the up-and-comers like Halsey and Towers had known better for years. Commented Aug 10, 2013 at 19:57
  • @T.E.D. The relevant thing is not if they "appreciated" carriers, but if they thought Japans fleet had the range to attach Pearl Harbor or not. Commented Aug 11, 2013 at 4:01
  • 10
    the USN was heavily divided. One school was all about battleships, and another school about airpower. And the latter itself was divided between carrier power and land based air. And then there were the submarine advocates, and a small group wanting to go all coastal with no more blue water navy in the light of US isiolationism making that an unneeded expense and provocation towards other countries.
    – jwenting
    Commented Aug 11, 2013 at 5:52
  • 1
    Although I don't quite but the argument, +1 for raising good points. Commented Aug 12, 2013 at 9:21

Question: Was the attack on the American forces at Pearl Harbor totally unexpected?

Short Answer

Commanders across the pacific had been warned for weeks of an impending Japanese attack. Specifically Admiral Kimmel and General Short in command at Hawaii's navy and army forces respectively, had responded to these warnings and taken steps to safeguard their commands from the Japanese attack. The US Military across the Pacific had been placed on high alert numerous times prior to Dec 7th. All false alarms. It was common knowledge written in bold letters in most of the major U.S. newspapers that a Japanese attack was imminent a week before Pearl Harbor. That was ultimately as much as US intelligence ever knew. An attack was about to occur but even US intelligence didn't know where, when(date) or what form the attack would take; thus all the fore warnings ultimately were not actionable. Specifically the actions taken by the commanders in Hawaii in response to the warnings played into the hands of the Japanese, seemingly(1).

As for the British double agent's report in the original question. He was asked by Japanese to report on US Navy Ship movements around Pearl Harbor and from this he concluded Hawaii was the target of the impending attack. Only the FBI had already cracked a much larger spy cell (Tachibana Case) involving Japanese navy personnel and civilians in June of 1941 who were reporting on US Navy movements from San Diego to Seattle. A single agent and his opinion would not have eclipsed all the other information US Intelligence was receiving, at least not without 20/20 hind site.

As for Tokyo / Washington D.C embassy dispatch sent in the clear which the FBI reportedly intercepted, I don't find that creditable. Operation Magic was a very successful intelligence operation operating for years reading every encrypted Japanese dispatch. It's existence was so secret that not even the FBI director J Edgar Hoover was aware of it.

Why would the Japanese send the time and location of their attack in the clear to their Embassy when over many months they didn't send such information in any of their encoded dispatches? Not even on the day of the Attack in what they considered their 14 part declaration of war. Why would the embassy even be alerted? The Japanese diplomats already knew all they needed to know to play their part.

(1) Seemingly: see Question #2 and conclusion.

Detailed Answer

A Japanese attack in the Pacific was very much expected. It was common knowledge among Naval Officers, enlisted, and civilians. Where in the Pacific and what form the attack might take was lesser known and the subject of much debate. The Philippines, Guam, Hawaii, Midway, Wake Island, the Panama Canal, even the west coast of the United States were all possible targets. Was the attack going to take the shape of an amphibious landing, saboteurs attacking American installations, domestic revolt among the nations minority populations encouraged by Japans military, or would it be attacking American ships at sea? All of these were deemed at least as likely as an aerial attack launched from aircraft carriers against Pearl Harbor.

Yes the United States Navy had broken the Japanese diplomatic code and were reading the diplomatic dispatches. These dispatches didn't yeild a straight declaration of war with a date, location and description the attack would take. Rather they contained indicators that Japan was preparing for an attack, like orders for the Japanese consulates to burn all diplomatic papers. The Operation was called Operation Magic and it wasn't nearly as helpful as some believe. Operation Magic informed us on Nov 5th 1941 that Nov 25th, 1941 was Japan's deadline for the decision on war. What does that mean? Every Commander in the Pacific was alerted. Then Japan changed their deadline to Nov 29th and again alerts were sent. Only those alerts predicted the war would begin on Sunday Nov 30th, 1941 and turned out to be wrong. No hint on where or how the Japanese were going to attack.

Source 1: 43 "Remember Pearl Harbor",
Source 2: The "Magic" background of Pearl Harbor
cable intercepted from Tokyo to Japanese Embassy in Washington DC read:

All the pacific military commanders received some warning on Nov 27 to expect a hostile move by Japan.

Although Pearl Harbor specifically had been identified several times prior to Dec 7th 1941 by intelligence agencies the information was never actionable. The accurate date of the attack, the location of the attack and the form the attack would take were not part of any Intelligence report prior to the telegram from Pearl Harbor to Washington DC saying an attack was under way. The problem was the same Intelligence reports which claimed Hawaii as a possible target also warning of attacks across the Pacific. In response to these warmings US forces in the Pacific had been put on high alert several times in the weeks leading up to Pearl Harbor, and the War Dept had even issued a formal warning of impending War. The United States navy issued a classified report Dec 4th, 1941 which even warned of African American revolt on behalf of Japan. That the report also lists Pearl Harbor as a likely target for imminent Japanese attack doesn't accurately represent the value of such reports which really were warning of attack everywhere, and had the effect of warning of attack nowhere except with 20/20 hind site.

Bottom line anybody who read the Sunday newspaper in the weeks leading up to Pearl Harbor knew almost as much as the folks reading the Japanese diplomatic dispatches. War was imminent. where, when exactly (date) or what form the attack was going to take was a mystery.

The evidence of US fore knowledge of the impending Japanese attack includes:

  • News Paper Headlines Nov 30th 1941 1 week prior to the Japanese Attack.

    • Hawaii Hilo Herald Tribune
      enter image description here

    • Boston Globe
      enter image description here
      enter image description here
      enter image description here

    • Chicago Sun
      enter image description here

    • Honolulu Advisor enter image description here

  • Strategically

    • The United States knew Japan was running out of oil. We knew their best target to alleviate this shortage was the Dutch East Indies oil fields (modern Indonesia). Japan had already moved in and occupied French Indochina (modern Vietnam, Cambodia). Right in the middle between Japanese forces and their impending target was the United States protectorate, the Philippines.

enter image description here

  • Increasing Japanese aggression
    • An American naval vessel the USS Panay in China on the Yangtze River, was targeted and sunk by imperial Japanese Forces Dec 12, 1937.
    • Japan had signed the Tripartite Pact with fascist Italy and Nazi Germany. Sept 27th, 1940
    • June 1941, A Japanese intelligence operation in the U.S. was uncovered. It was a sensational case which demonstrated to the public Japan's interest in keeping track of US Naval assets on the west coast of the U.S. Tachibana Case
    • Japanese Military build ups in French Indochina, were occurring in late Nov and early Dec 1941 which the President expressed concern to Japan.
      enter image description here
  • Precedent
    • The battle of Taranto Nov 12 1940, Britain destroy half of the Italian Navy's capital ships in a single evening attack, from the air, launched from a British aircraft carrier in the Med.
  • On Dec 6th 1941 President Franklin Delano Roosevelt sent a personal appeal to the Japanese Emperor for peace. - FDR Library
    enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here

  • Secretary of War Henry L. Stimson's diary entry for November 25, 1941. The U.S. Secretary of war details discussion which occurred at a "War Cabinet Meeting" at the White House with President Roosevelt, himself, Secretary of State Cordell Hull, Secretary of the Navy Frank Knox, Army Chief of Staff George C. Marshall, and Chief of Naval Operations Harold R. Stark. The Quote is:

There the President, instead of bringing up the Victory Parade [which, in Stimson's words, was "an office nickname for the General Staff strategic plan of national action in case of war in Europe"', brought up entirely the relations with the Japanese. He brought up the event that we were likely to be attacked perhaps (as soon as) next Monday, for the Japanese are notorious for making an attack without warning, and the Question was how we should maneuver them into the position of firing the first shot with out allowing too much danger to ourselves. It was a difficult proposition. source

  • Numerous war warnings had been sent by the US Military to commandeers across the Pacific in the weeks leading up to Pearl Harbor warning of impending attacks.
  • Dec 4th, Roosevelt received a classified report from the Naval Dept saying war with Japan was imminent and naming Hawaii as a target.
  • Naval Inteligence officers reading the communications between Japan's embassy in Tokyo and Washington DC told FDR Japan would attack and Hawaii was the target only they projected the date of the attack Sunday Nov 30th, 1941.

Question #2 . If (It was expected), why did no one alert defense forces to protect Pearl Harbor?

None of the sources predicting attack were particular helpful to the commanders in the Pacific much less Hawaii. One report saying Pearl Harbor would be attacked on Dec 7th 1941 would have been of some use, but many reports sent out across the pacific predicting imminent attack everywhere which were continuously wrong became mind numbing. It can be argued non specific warnings of attack on Pearl Harbor had the opposite effect on preparedness. How do you prepare for an attack given you don't know what form that attack will take? Admiral Kimmel the commander in charge of the Pacific Fleet, as well as General Short his Army counterpart, neither of whom had any knowledge of Operation Magic, took counter measures in response to the warnings to protect their assets which in hind site helped the Japanese attackers.

43 "Remember Pearl Harbor"

Admiral Kimmel considered, but rejected the idea of taking his fleet out of Pearl Harbor. In open water, he felt the ships would be too vulnerable. His 4 carriers were not available to provide air cover. (3 were bringing warplanes to other Pacific Islands, 1 was back in San Diego for repairs). Kimmel believed his ships were safer in Hawaii's protected harbor watched over by several hundred US Army warplanes stationed at Hawaii bases.

43 "Remember Pearl Harbor"

US Army General Short responded to the war warnings by moving to protect his air planes from sabotage rather than air attack. He moved all his airplanes to the center of fields where they were bunched wing tip to wing tip. This way they could be more easily protected from Japanese infiltration and saboteurs. This made the army air corps planes easier targets for the Japanese pilots in the Dec 7th air attack, but General Short given the vagueness of the warnings he recieved, considered Hawaii's large Japanese population the greater threat.

Again neither commander knew Washington had broken the Japanese diplomatic codes, but in truth even if they had access to the Japanese dispatches in real time they wouldn't have had more information than that which they acted upon. Both commanders had received numerous warnings of impending attack. Both commanders took steps to safeguard their commands which ultimately assisted the Japanese attacks rather than their intended purpose. The magic diplomatic dispatches never contained the smoking gun which would have given Kimmel and Short actionable information beyond attack was imminent but god knows where.

The final part of a 14 part diplomatic Message between Tokyo and and their embassy in Washington DC was decoded just prior to Pearl Harbor. During the Tokyo War Crimes Trial, Japan's Prime Minister Tojo would point to this dispatch as his formal declaration of war and blame the Embassy personnel who delivered it for it's tartiness. Only it didn't mention War, nor did it mention Pearl Harbor, much less air attack from Carriers. Operation Magic never produced actionable information on an impending attack on Pearl Harbor. Nearly everything Operation Magic had Sunday 8am Dec 7th 1941, could have been read in the newspaper on Sunday Nov 30th, 1941 in any city in the country. War was imminent.

In Conclusion..

If you really want to blow your mind it can be argued that if the American Pacific Fleet had put out to sea, the Pearl Harbor raid would have been much more successful for Japan. Bombing the US Navy's ships primarily it's battleships monopolized the attention of the Japanese pilots. It can be argued the real targets of the Pearl Harbor raid should have been:

  • the ship yards vital to maintain and repair ships
  • the fuel reserves several million barrels worth which would allow ships and airplanes to operate extended from US coast thoughout the coming Pacific War.
  • the submarine base which would contribute to the crippling of the Japanese economy in WWII
  • the Navy HQ building which not only contained most of the US commanders for the coming Pacific war but also the cryptology department which greatly contributed to the winning/shortenning of the war.

In the Pearl Harbor raid all of these important targets were left un-molested while the Japanese concentrated on the US Navy Ships; Specifically the battleships. Considering, of the twenty-one ships that were damaged or lost in the Pearl Harbor attack, all but three were repaired and returned to service. USS Arizona, USS Oklahoma, and the older Battleship USS Utah were the only ships sunk at pearl harbor which were not returned to action.

Attack on Pearl Harbor

  • Arizona (RADM Kidd's flagship of Battleship Division One): hit by four armor-piercing bombs, exploded; total loss. 1,177 dead.
  • Oklahoma: hit by five torpedoes, capsized; total loss. 429 dead.
  • West Virginia: hit by two bombs, seven torpedoes, sunk; returned to service July 1944. 106 dead.
  • California: hit by two bombs, two torpedoes, sunk; returned to service January 1944. 100 dead.
  • Nevada: hit by six bombs, one torpedo, beached; returned to service October 1942. 60 dead.
  • Pennsylvania (ADM Kimmel's flagship of the United States Pacific Fleet):[115] in drydock with Cassin and Downes, hit by one bomb and debris from USS Cassin; remained in service. 9 dead.
  • Tennessee: hit by two bombs; returned to service February 1942. 5 dead.
  • Maryland: hit by two bombs; returned to service February 1942. 4 dead (including floatplane pilot shot down).
  • Utah: hit by two torpedoes, capsized; total loss. 64 dead

It can be argued that if the Japanese pilots weren't pre-occupied with bombing US battleships they might have chosen some of the more valuable targets all of which would play a more significant role than battleships in the coming Pacific War.

The Japanese confidence in their ability to achieve a short, victorious war meant that they neglected Pearl Harbor's navy repair yards, oil tank farms, submarine base, and old headquarters building.[56] All of these targets were omitted from Genda's list, yet they proved more important than any battleship to the American war efforts in the Pacific. The survival of the repair shops and fuel depots allowed Pearl Harbor to maintain logistical support to the U.S. Navy's operations,[137][138] such as the Doolittle Raid and the Battles of Coral Sea and Midway. It was submarines that immobilized the Imperial Japanese Navy's heavy ships and brought Japan's economy to a virtual standstill by crippling the transportation of oil and raw materials: by the end of 1942, import of raw materials was cut to half of what it had been, "to a disastrous ten million tons", while oil import "was almost completely stopped".[nb 20] Lastly, the basement of the Old Administration Building was the home of the cryptanalytic unit which contributed significantly to the Midway ambush and the Submarine Force's success.


@ed.hank additionally how the USN silo'd their various intelligence groups (hawaii, cavite, etc.) prevented the sharing of information between each other which prevented a full picture from being developed.

That Japan was going to attack in the Pacific was common knowledge in late Nov - Dec 1941. Anybody who could afford a newspaper in any city in the country knew as much as US Intelligence. No US intelligence agency accurately predicted the location of the attack or the form that attack would take in a meaningful actionalbe way. Even the Diplomatic Intercepts from Operation Magic didn't yield such information, beyond war was imminent. Of the final 14 part communication Japanese officials would claim was their formal declaration of War at the Tokyo War Crimes Trial, which Magic intercepted from Tokyo to their DC embassy, Hawaii wasn't mentioned nor was war. The most damning statement it contained was that it was "impossible to reach an agreement through further negotiations.".

Given that if every American in Nov of 1941 was given access to the most classified US Magic Intercepts, they arguable wouldn't have had better information than if they just read the Sunday paper regularly.

David Thornley It's not on topic for this question, but Alan Zimm, "Attack on Pearl Harbor: Strategy, Combat, Myths, Deceptions", pp. 308-321 are about why attacking the shore facilities would have been mostly futile, doing minimal permanent damage. The Japanese aircraft available were much better suited for tactical than strategic attacks. –

Even a bomb from a tactical aircraft could ignite 4.5 million barrels of aviation fuel.

enter image description here

Pearl Harbor Historical Org
Gordon Prange, (General Douglas MacArthur's chief Historian, twice NY Times best selling author, and tenured professor of history) one of the most renowned Pearl Harbor historians, wrote damningly: “By failing to exploit the shock, bewilderment, and confusion on Oahu, by failing to take full advantage of its savage attack against Kimmel’s ships, by failing to pulverize the Pearl Harbor base, by failing to destroy Oahu’s vast fuel stores, and by failing to seek out and sink America’s carriers, Japan committed its first and probably its greatest strategical error of the entire Pacific conflict.”

Admiral Yamamoto was critical of Admiral Chuichi Nagumo failure to lanch the third wave against Pearl Harbor which was meant to attack the fuel farms and dry docks as well as other strategic targets meant to maximize the successes of the first two waves, and make the Pacific base useless to US forces for the coming war. Naguma was a controversial choice to lead the attack on Pearl Harbor. He had disagreed with the attack and argued against it. Naguma had lost only 29 aircraft in the first two waves but decided to push away from the table and not risk any further aircraft. It was probable Japan's largest mistake of the war.

David Thornley
@JMS Pearl Harbor attack planners couldn't know about the results of the Battle of Midway. Destruction of half the oil tank farm would have required repair and resupply, both of which were feasible. I am aware of what Nimitz said, and I think he was dead wrong on that. FWIW, Zimm suggests that Nimitz would have been far more effective when solving a problem than when idly thinking about it. –

Oddly enough Admiral Yamamoto who was the originator of Pearl Harbor predicted Midway almost to the day. Yamamoto spoke English fluently had graduated from Harvard and was Naval Attache in Washington D.C. Yamamoto believed Pearl Harbor would only ever by Japan six month, given America's industrial power. Almost to the day he was right.

Isoroku Yamamoto When asked by Prime Minister Fumimaro Konoe in mid-1941 about the outcome of a possible war with the United States, Yamamoto made a well-known and prophetic statement: If ordered to fight, "I shall run wild considerably for the first six months or a year, but I have utterly no confidence for the second and third years." His prediction would be vindicated as Japan easily conquered territories and islands for the first six months of the war until it suffered a shattering defeat at the Battle of Midway on June 4–7, 1942, which ultimately tilted the balance of power in the Pacific towards the US

David Thornley
@JMS Destruction of half the oil tank farm would have required repair and resupply, both of which were feasible.

Yes of coarse but it would have taken years. Hundreds of millions of barrels of oil. As I previously stated.

David Thornley I am aware of what Nimitz said, and I think he was dead wrong on that. FWIW, Zimm suggests that Nimitz would have been far more effective when solving a problem than when idly thinking about it. –

David, I think Nimitz and Yamamoto are two of the greatest most respected Admirals in the history of Naval Warfare. Certainly of WWII. Yamamoto was Japan's greatest Navel strategist and Nimitz the man who defeated him. To my mind their statements speak for themselves. I'm going to re-read and revisit your other suggestions and see what I can add to my answer to make it stronger. Thank you for taking the time and favoring me with your thoughts. Early on I thought you had good points and that didn't come across in my earlier responses enough.. I was especially interested in your objections on the third wave. Reading up on that I found a lot of sources which support you and now I even question whether a third wave was part of initial attack plan or something necessitated by the first two waves.

right now I have to get back to work, so I'll get on that after the face.

  • 3
    additionally how the USN silo'd their various intelligence groups (hawaii, cavite, etc.) prevented the sharing of information between each other which prevented a full picture from being developed.
    – ed.hank
    Commented Jan 5, 2019 at 16:37
  • @ed.hank. Responded to your comment at the end of my answer above.
    – user27618
    Commented Jan 7, 2019 at 20:26
  • It's not on topic for this question, but Alan Zimm, "Attack on Pearl Harbor: Strategy, Combat, Myths, Deceptions", pp. 308-321 are about why attacking the shore facilities would have been mostly futile, doing minimal permanent damage. The Japanese aircraft available were much better suited for tactical than strategic attacks. Commented Jan 7, 2019 at 23:20
  • @DavidThornley responded in my answer.
    – user27618
    Commented Jan 8, 2019 at 0:07
  • The Combined Fleet Operation Order listed shore and port facilities as lower priority than anything that floated or flew. There were still a good many ships afloat in Pearl Harbor, so that a third strike should have been against them. Commented Jan 9, 2019 at 18:42

If the question is

Did the US Administration expect an attack at Pearl Harbor by significant Japanese forces?

then the answer HAS to be NO.

The US Pacific Fleet was concentrated and headquartered in Hawaii. The US Army was responsible for the defense of Hawaii, on the ground but more importantly in the air. There was no illusion anywhere that the Army had the means to detect an impending attack. The Air Corps had nowhere near the long range aircraft that a proper defense required. Radar was unproven both as to equipment and personnel. But the Fleet was concentrated there and clearly not properly defended. One has to conclude that there was no sense that the Japanese would launch a major attack on Hawaii.

War was seen as a very real possibility, that is why the Fleet was at Pearl Harbor and not on the US West Coast. The Pacific Fleet was essential for the defense of the Philippines, and Hawaii was much closer than the US West Coast. Although individuals may have seen a possibility of a significant Japanese attack as far from its home waters as Hawaii, this does not seem what the US Administration (senior civilian and military leaders) imagined. Submarines and 5th columnists were the most obvious threats.

While a Japanese attack on US assets was not surprising, the major attack on Hawaii was. US intelligence saw Japanese aggression, but that intelligence did not vector toward Hawaii. Even if an FBI agent thought there was a statement about Hawaii in an intercept, the US Military had the same intercepts and did not, apparently, have the same analysis.

Based on what was done, rather than what the Administration knew or imagined or what we think we know today, there was no expectation of a major Japanese attack on Hawaii. Based on what was actually done by the US administration, the only other explanation for events was that the US Pacific Fleet was bait for the Japanese. That I find very hard to accept.

  • There's also the possibility that the strength of the defenses was overrated, or that the defenses would have been much better if not for General Short's actions. Commented Jan 8, 2019 at 21:07
  • @David Thornley...The defenses did seem adequate to meet a surface sea threat or external. ground attack. No matter what permutations went through the heads of Kimmel and Short, they understood their principle threat to be local and internal. Of course, both would have loved to have the capability of a 24/7 long range air sweep of the waters around Hawaii.. They knew they did not have that, and Washington knew the same. The Fleet and Air Corps were concentrated to meet the threat that seemed real. Maybe there is another possibility: all senior officials from Washington to Hawaii were stupid.
    – J. Taylor
    Commented Jan 8, 2019 at 21:46
  • The defenses were quite adequate against ground and surface ship attack. It wasn't Kimmel's job to defend the base; General Short's job was to protect the fleet in harbor so it could have a safe place. Short was told to expect air attack, and, indeed, he got an air attack. He had made preparations against sabotage that made his aircraft almost completely useless against air attack. The senior officials in Washington made the mistake of thinking Short took his duties seriously (by WWII standards, Pearl Harbor was a quite distant post, and Short should have been competent .) Commented Jan 10, 2019 at 14:13
  • @David Thornley.....The question involved expectations. If a serious air attack had been expected then the Pacific Fleet would not have been concentrated within an area of a few thousand meters. Rainbow 5 and Dog Plan, along with other planning, anticipated troubles in the Far East which would trigger the "Triangle" defense of Alaska-Hawaii-Panama Canal. The Naval and Air assets were concentrated to meet what seemed the most likely threat. And there were issues with peace time personnel . Some time before Dec. MacArthur ordered the Far East AF dispersed. . Brereton did not see to it.
    – J. Taylor
    Commented Jan 10, 2019 at 20:57

It DOESN'T matter.

It was unexpected. And total surprise was achieved.

Any government anywhere is a massive organization, made up of thousands, tens of thousands, in some cases millions of people.

When you have that many people.. you have that many opinions..

In many cases, the job is to write reports and interpretations of events.

In virtually every event that counted in human history, someone correctly guessed the intentions of the opposition.

But this only counts if the government adopts his/her view.

So Sure someone was able to guess that the Japanese intended to attack Pearl Harbor. But he couldn't convince his superiors, so it amounted to nothing.

This kind of stuff happens all the time.

It is just how it is.

  • 1
    These are opinions that are not responsive to the question.
    – MCW
    Commented Jan 7, 2019 at 17:10

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