The entire submarine force was under the command of Vice Admiral Shimizu Mitsumi, C-in-C of the Sixth Fleet, who accompanied the advance force to a point short of Oahu on board his flagship, the cruiser Katori. The submarines departed Kure and Yokosuka Naval Stations between 18 and 20 November for rendezvous and final refueling at Kwajalein in the Marshalls. (A few, delayed in leaving Japan, proceeded directly to Hawaii.) Yamamoto had permitted the participation of this more conventional naval force in the operation on the grounds that, according to the tactical war games projections, aircraft alone were not likely to destroy the American battle line. Fuchida, however, was said to be furious about their inclusion. First, the confident airman argued, they were not needed. Second, they presented the serious risk of compromising the air attack if one of their number was detected prematurely. He would be proven right on both counts.35
* * *
While these movements of ships and boats were under way, the Japanese Foreign Ministry and military engaged in a number of calculated deceptions. On 7 November, the date when Y-Day was set, an unnamed Japanese, reportedly acting at the request of Foreign Minister Togo, visited Ambassador Grew and urged “repeatedly” that, irrespective of the merits of the Japanese diplomatic position, it was “of the highest importance that the Washington conversations be continued and not [be] permitted to break down.”36 Equally insistent were Togo’s messages later to his negotiators in Washington, Nomura and Kurusu. On 28 November, when the Striking Force was well out to sea on its passage to Hawaii, the foreign minister sent the following signal: “In two or three days the negotiations will be de facto ruptured. This is inevitable. However, I do not wish you to give the impression that the negotiations are broken off. Merely say to them [Secretary Hull and his aides] that you are awaiting instructions.” Four days later, Togo told them that “the date set [29 November] has come and gone and the situation continues to be increasingly critical. However, to prevent the United States from becoming unduly suspicious we have been advising the press [that] … the negotiations are continuing.”37 These “deceit plan messages,” as they came to be called, were decrypted and read in Washington, though knowledge of their content was not shared with Kimmel or Short.
On the military side, sailors from the Yokosuka Naval Barracks were sent on liberty to Tokyo and Yokohama on highly visible sight-seeing tours to project an image of ordinary peacetime casualness. And the Pacific liner Tatsuta Maru, with a full passenger list, including Americans who wished to evacuate, was permitted to depart Yokohama for Honolulu and San Francisco on 2 December; though she reversed course on the eighth (Japan time) upon receipt of orders from the Navy Ministry. In accordance with the deception plan, the Striking Force proceeded to the Kuriles under strict radio silence. The Morse code sending key that was wired to the continuous wave radio transmitter on each ship was sealed or dismantled, and in some cases fuses were removed from the circuitry, to ensure that the attack fleet was dumb but not deaf, so as to preclude the possibility that an errant transmitted signal might give away the position of the carriers to American direction-finding (DF) receivers. Oscilloscopes attached to those receivers, furthermore, could distinguish the transmission patterns of the various ships, e.g., those of the Akagi from those of the Kaga. That imposition of radio silence, say all the Japanese who oversaw or participated in the raid and who wrote or spoke about it in later years, remained in force until the launch of aircraft on 7 December.38 In the meantime, communications between ships were conducted by means of signal flag by day and blinker light by night.
* * *
When were the Japanese carrier pilots told of the objective for which they had been training? The question admits of several answers depending on the witness speaking. One carrier pilot told postwar interrogators that all officer pilots—but no petty officer or enlisted—were briefed on the operation aboard the Akagi in Shibushi Bay on 5 October. The briefers were Yamamoto and the chief of staff of the carrier fleet, Rear Admiral Kusaka Ryunosuke. The pilots were told, said this unnamed source, that the attack would be made on 8 December (Japan time). A second carrier pilot, identified as Shiga Yoshio, independently confirmed the particulars of the foregoing account, including the site and the roles of Yamamoto and Kusaka, but differed on the date, which he set at 5 November. According to Shiga, the pilots’ reaction to the briefing was one of general pessimism: “All felt that it was a suicide mission.”39 These two interrogation responses bear about them an air of unreality. First, it is not credible that pilots would be briefed by the C-in-C Combined Fleet. Second, Yamamoto had not even by the latter date issued his Order No. 1 establishing 8 December as Y-Day.
Far more likely is the date of 23 November given by historian Gordon W. Prange, based on extended interviews he conducted with Kusaka, Genda, and Fuchida. On that date, which was one day after the Striking Force had assembled in its jump-off point, Tanken (Hitokappu Wan) Bay, and on board the flagship, carrier Akagi (Red Castle), force commander Vice Admiral Nagumo Chiuchi went over their destination and targets with the captains and staffs of the carriers, battleships, cruisers, and destroyers, as well as with the three submarine skippers and the commanding officer of the tanker fleet. He explained that if during their passage to Hawaii there should be an agreement struck in the Washington negotiations the Striking Force would be ordered to return to home bases without executing. Similarly, he told his commanders and staffs, should the force be detected by the enemy prior to or on X-Day minus two, the force would reverse course. If discovered on X-Day minus one, however, he, Nagumo, would make a decision whether to continue the advance, based upon the circumstances. If an enemy force confronted them on X-Day, Kido Butai would fight it out with them at sea, calling up the remaining vessels in the Inland Sea for reinforcement.40
Nagumo seems to have been of two minds on the question of how many attacks should the Striking Force make on Pearl Harbor and the Oahu airfields. On the one hand, he told his commanders that their single two-wave morning attack, as planned, should be sufficient to cripple, if not altogether destroy, the U.S. Pacific Fleet. On the other hand, he issued under the same date Operation Order No. 3 that stipulated (as Genda and Fuchida had been pressing) that “if the land-based air power has been completely knocked out, repeated attacks will be made immediately in order to achieve maximum results.”41
On the same day, after lunch, Nagumo told the assembled officer pilots for the first time that they were going east to attack Pearl Harbor. On hearing the news, according to Fuchida, quite aside from pessimism, “their joy was beyond description.”42 Genda and Fuchida then provided the young airmen a day-and-a-half-long (23–24 November) detailed briefing on the attack. There would be two waves of aircraft, they informed them, the first to launch when 230 nautical miles north of Oahu, timed to arrive over Pearl Harbor and surrounding airfields at about 8:00 A.M. Hawaii time; the second to launch from 200 miles out, timed to arrive over targets at about 0900. Fuchida himself would lead the first wave, consisting of fighter aircraft (Mitsubishi A6M2 Type 21 Reisen Zero), torpedo bombers (Nakajima B5N2 Type 97 Kate), high-level (horizontal) bombers (the same Type 97, each fitted with one 1,760-pound armor-piercing gravity bomb), and dive-bombers (Aichi D3A1 Type 99 Val). Lt. Comdr. Murata Shigeharu would lead the centrally important torpedo flight.
The second wave, consisting of all types except torpedo bombers—they were expected to be too vulnerable to AA fire after their surprise use in the first wave—would be commanded by Lt. Comdr. Shigekazu Shimazaki. The two waves would be preceded by a flight of two Aichi E13A1 “Jake” reconnaissance floatplanes with three-man crews catapulted from the heavy cruisers Tone and Chikuma. Their purpose was to determine what ships of the U.S. fleet were at Pearl Harbor and which (if any) were at Lahaina Roads on the neighboring island of Maui. The scouting period over targets was set to last one hour, but when Murata and other pilots objected that the planes’ necessary breaking of radio silence and their subjection to sighting might jeopardize the critical element of
surprise, it was agreed by Genda, Fuchida, and, later Nagumo, to halve the time to thirty minutes.
Genda went over the sequence and spacing of takeoffs from the six carriers, the process of forming up aloft, the courses to be flown, rendezvous points, changes in altitude to be executed, and the exact approach routes to targets. He emphasized that the essential ingredients of success were teamwork, surprise, timing, and simultaneity of attacks. For example Murata’s flight of forty torpedo bombers would divide into two groups and strike the battleships and cruisers moored to the southeast and northwest of Ford Island from two different directions at the same time. Fuchida explained the various signals that he would use during the first wave’s approach to targets. Upon reaching the northern tip of Oahu, he would fire one flare if it appeared that the aircraft had caught the enemy with his guard down, in which case one particular sequence of attacks would take place; he would fire two flares if it appeared that the enemy had been alerted, in which case another, different, sequence would be followed. And if, when Pearl Harbor came into view, Fuchida was convinced that surprise had indeed been achieved, he would break radio silence and signal the carriers: “Tora! Tora! Tora!” (“Tiger! Tiger! Tiger!”)
In daylong breakout sessions with twenty-six separate groups of pilots, Fuchida went over the operation in exacting detail. Using models of Pearl Harbor, and Oahu, with miniature mock-ups of ships and ground installations, as well as maps and diagrams, he pinpointed each group’s targets and approach routes, and drilled the officers (and their enlisted personnel) on their responsibilities until they had them thoroughly memorized.
It was the last time that Genda and Fuchida had the air crews of all the carriers together, and they made the most of it. Neither wanted to dampen the enthusiasm of the pilots, but Fuchida had to acknowledge to them the possibility that the American fleet would not be in the harbor and could not be found. In that disappointing event, Fuchida told interrogators after the war, “we would have scouted an area of about 300 miles around Oahu and were prepared to attack. If the American fleet could not be located, we were to withdraw.” (Interestingly, no mention was made of attacks instead on land installations such as repair facilities and the fuel farms.) The carriers would take up station about fifty miles south of Oahu, recover their scouting aircraft, and retire to the Marshalls to await further instructions.43
There were many such imponderables facing Nagumo, Genda, and Fuchida, not in any particular order: Suppose the American defenders had distant aerial reconnaissance under way in the sector north of Oahu—agents associated with the consulate in Honolulu had not reported any—where Nagumo’s carriers would make much of their final dash toward launch position in full daylight, and suppose the skies overhead were clear, what then? Suppose American naval intelligence had divined the Japanese intention and, even now, was preparing to ambush the Kido Butai (as U.S. Navy carriers, acting on superb intelligence, would trap the Japanese in the Battle of Midway [4–6 June 1942], when Nagumo again was task force commander). Suppose fog socked in the carriers on X-Day, foreclosing the possibility of recovering aircraft, thus causing Japanese air losses to be higher than those of the Americans? Suppose the negotiators in Washington reached an accord, and the Hawaii expedition was recalled, and the Americans then reneged: could a surprise operation be remounted weeks or months later when thousands of sea and air crewmen were privy to the secret?
* * *
Following last-minute preparation of the ships for battle, which included the rigging of rolled mattresses (mantelets) around the exterior of bridge and island structures to protect against bomb splinters, Nagumo’s formidable armada weighed anchor and sortied into the North Pacific. The time was 0600 on 26 November (Japan time). Chief Ordnance Officer Sadao Chigusa, on board the destroyer Akigumo, wrote in his diary, “0600. At last we left Hitokappu Bay for Hawaii to attack Pearl Harbor, seeing M[oun]t Berumarube disappear behind us.… A northwest wind of 5–6 m/second (10–12 knots) blew, and it was very cold with occasional gusts of driving snow.… The sally of our great fleet was really a majestic sight.”44 Kido Butai steamed east at a steady 12 to 14 knots, the carriers in parallel columns of three, with the tankers trailing. The two battleships and two heavy cruisers flanked the carriers. The light cruiser and the destroyers formed the perimeter, or screen. The three submarines advanced at twenty-three knots to take up scouting stations 200 miles ahead.
The course chosen, 095 degrees, would take the fleet through the “Vacant Sea,” which was practically devoid of commercial shipping, between the southern routes that lay between Hawaii and the ports of China and the northern great circle routes that lead near the Aleutians. Two other courses had been considered. One, a central route, would have taken the fleet directly toward the Hawaiian archipelago; the other, a southern route, would have passed the fleet through the Marshall Islands to the southwest of Hawaii. Both had the advantage of providing calm seas for refueling, as against conditions in the Vacant Sea, which normally offered twenty-four days of storm for every seven days of calm. But both posed dangers of encountering commercial vessels en route and of being sighted by U.S. Navy patrol flights out of Wake, Midway, Palmyra, and Johnston Islands. The refueling problem presented by gale winds and heavy seas on the northern route could be overcome, it was decided, by training. Too, the very improbability of a punishing North Pacific crossing assisted in the deception plan. Maintaining surprise was the overriding key to a successful operation. Hence the 095 degree heading, on which, to its own surprise, the fleet found fair seas during its first six days. The choice of Sunday, 7 December (Hawaii time) for the attack was owed primarily to the fact that, as the Honolulu consulate had reported, the U.S. Pacific Fleet followed the habit of entering harbor on Friday or Saturday after exercises and of departing on Monday or Tuesday. Also the Sunday date coordinated well with attacks scheduled in the Southern Operation.
The first refueling at sea of four of the carriers and the cruisers took place five days out. We know that the carrier Kaga took an oiler in tow, distance apart seventy to eighty meters, using a manila hauser about six inches in diameter; after the tow was passed, and speed of the vessels was reduced to eight knots, fuel was passed through a hose about eight inches in diameter, rubber outside, metal inside, supported by a two-inch wire jackstay. Fuel intakes were fitted on both quarters of Kaga. Oiling took about six hours. Carriers Soryu and Hiryu, though the fastest of the carriers, had the lowest fuel capacities (4,000 metric tons), hence they had to be replenished daily. Fuel tanks on the short-legged destroyers had to be topped off every other day. From the diary kept by her ordnance officer, we learn that the newly commissioned destroyer Akigumo, replenished whenever the opportunity presented itself, day or night, with the donor tanker either alongside or astern.45 Visibility was usually so bad when the tankers approached the warships that towing spars for position-keeping were almost constantly in use.
Meanwhile, all ships posted lookouts as a guard against possible U.S. air interdiction. Kaga, for example, had twenty-one sure-eyed men on two-hour tricks manning seven AA machine-gun positions around the clock. But no enemy aircraft would be sighted during the voyage; nor would any warships. Encountering U.S. flag merchant shipping was no problem, since on the day after the 16 October war warning OpNav had ordered all merchant transpacific traffic diverted to a southern route that ran well clear of the Japanese mandates, south through the Solomon Islands, then west of the Santa Cruz Islands, then through the Torres Straits between Australia and New Guinea, “taking maximum advantage of Dutch and Australian patrolled areas.”46 Nagumo may have learned of this course alteration from Japanese intelligence.
In ships’ radio shacks operators listened for the latest encrypted intelligence on Pearl Harbor. It came from consular agents in Honolulu, relayed to Kido Butai through the Imperial General Staff, with unexplained delays of three to five days. Thus, the report “Activities in Pearl Harbor as of 0800/28 November [Hawaii time]” reached the ships on 2 December [Japan time]. It re
ad:
Departed: 2 battleships (Oklahoma and Nevada), one carrier (Enterprise), 2 heavy cruisers, 12 destroyers. [This was Halsey’s Task Force 8 ferrying Marine F4Fs to Wake. He in fact took nine destroyers.]
Arrived: 5 battleships, 3 heavy cruisers, 3 light cruisers, 12 destroyers, 1 tanker.
Ships making port today are those which departed 22 November.
Ships in port on afternoon of 28 November estimated as follows:
6 battleships (2 Maryland class, 2 California class, 2 Pennsylvania class).
1 carrier (Lexington).
9 heavy cruisers (5 San Francisco class, 3 Chicago class, and Salt Lake City).
5 light cruisers (4 Honolulu class and Omaha).47
Operators listened, too, for special code phrases, the meanings of which would be known to cryptographers on board the flagship Akagi, phrases such as “the fate of the Empire,” “the cherry blossoms are all in their glory,” and the one for which Nagumo anxiously awaited:
THIS DISPATCH IS TOP SECRET. THIS ORDER IS EFFECTIVE 1730 ON 2 DECEMBER COMBINED FLEET SERIAL 10. CLIMB NIITAKAYAMA 1208 REPEAT 120848
Niitakayama was the highest mountain in Japanese-occupied Korea. The code phrase was the order to “Proceed with attack.” The 1208 (8 December Japan time) was the date for the attack.
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