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Intelligence
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 (and perhaps from family members as well)
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.
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. |
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Imperial Japanese navy's orders,
directives and setup
The attack force Kido Butai:
November 26, 1941, the day the Hull note was sent, the Kido Butai sortied.
Commanded by Admiral Chuichi Nagumo, the carrier battle group, departed Hitokappu
Wan in the Kuril Islands under strict radio silence. The First Air Fleet comprised
of Carrier Divisions One, Two, and Five, escorted by Battleship Division Three,
Cruiser Division Eight, and Destroyer Squadron One and Divisions Seventeen and
Eighteen, screened by the Seventh Submarine Fleet, with logistic support from
1st and 2nd Supply Trains. It was the most powerful carrier force with the greatest
concentration of air power in the history of naval warfare to date.
The six aircraft carriers, which embarked
359 airplanes, were Akagi (flag), Kaga, Soryu, Hiryu, and the newest, Shokaku
and Zuikaku, with 135 Mitsubishi A6M Type 0 fighters (Allied codename "Zeke",
commonly called "Zero"), 171 Nakajima B5N Type 97 torpedo bombers
(Allied codename "Kate"), and 108 Aichi D3A Type 99 dive bombers (Allied
codename "Val") aboard. Two fast battleships, two heavy cruisers,
one light cruiser, nine destroyers, and three fleet submarines provided escort
and screening. In addition, the Advanced Expeditionary Force included 20 fleet
and five two-man Ko-hyoteki-class midget submarines, which were to gather intelligence
and sink U.S. vessels attempting to flee Pearl Harbor during or soon after the
attack. It also had eight oilers for fueling. |
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On December 1, 1941 Chief of Staff Fleet
Admiral Nagano gave a verbal directive to commander of the Combined Fleet Admiral
Isoroku Yamamoto informing him:
Japan has decided to open hostilities
against the United States, Great Britain, 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.
[The Kido Butai's (Striking Force)
objective was] 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.
Upon completion, the force was to return
to Japan, re-equip, and re-deploy for "Second Phase Operations". Finally,
Order number 9, issued 1 December 1941 by Nagano, ordered Yamamoto to "smash
the enemy fleets and air forces in the Orient and at the same time will intercept
and annihilate enemy fleets should they come to attack us ... occupy immediately
the key bases of the United States, Great Britain, and the Netherlands in East
Asia ... [and] capture and secure the key areas of the southern regions."
On the home leg, the task force was instructed
to counter-attack should American forces locate and engage them, and re-routed
south to the friendly base in the Marshall Islands. |
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Preparedness of 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, none specifically
indicated an attack against Pearl Harbor, nor has any doing so been identified
since. 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, probably
with attacks in the Far East: the Philippines, IndoChina, Thailand, or Russia.
The warnings were not specific to any area, noting only war with Japan was expected
in the immediate short term 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 obsolescent and 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. |
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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, and can be blamed in part on lack of manpower. At best, the information
was fragmentary, contradictory, or poorly distributed, and was almost entirely
raw, without supporting analysis. It was also incompletely understood by decision
makers. 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 safely out of harm's way. 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 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 tests demonstrated shallow-water aerial torpedo attacks
were possible, but no one in charge in Hawaii fully appreciated its import.
A war game surprise attack against Pearl Harbor in 1932 had been judged a success
and to have caused considerable damage. |
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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
interfere with ordinary operations. And as a result of limited numbers of long-range
aircraft (including Army Air Corps bombers, responsible for search by a prewar
arrangement), 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 fewer 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); even the British, which had contracted for them, 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 the 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 (uncontradicted) interpretation of the war warnings.
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