Sometime in early September 1941 key staff officers of the First Air Fleet gathered in Kusaka’s cabin aboard Akagi.1 When the last man had taken his place, Kusaka said in his customary understated style, “In case of war with the United States, Yamamoto plans to attack the U.S. Fleet in Pearl Harbor. The First Air Fleet’s mission is to carry out this operation.”2 Although everyone present gave Kusaka his close attention, the message was not new to some of them. But this marked the first occasion that Nagumo’s operational staff had been informed individually and collectively of Yamamoto’s adventurous project.
Kusaka briefly reviewed the general nature of the plan and emphasized the necessity for the strictest possible secrecy to ensure surprise. “You will now pool your resources,” he continued, “and begin a serious study of all the problems involved—air training, communications, intelligence, navigation, weather conditions, refueling at sea, route to Hawaii and the like. You face a big task, one that will require your very best efforts.”
Kusaka named Genda chief of the study group. He also assigned to Genda as his personal responsibility the air training, attack techniques, point of departure, and route to Hawaii. “You will coordinate the work of all the other staff members and report directly to me,” Kusaka charged him.
Senior Staff Officer Oishi would assist Genda and maintain his usual relations with Nagumo and Kusaka, while the others devoted their energies to their respective specialties.3 Ono tackled such communications problems as ship-to-ship signals en route, reception of messages from the homeland, radio silence, and other matters of communications security. Sasabe handled navigation and weather forecasting—distances to be covered, schedule of cruise, sea conditions, task force formation, and the like. Sakagami dealt with the difficult questions of fuel supply and refueling at sea—the fuel capacity of the various ships, amount and rate of consumption, speed of the task force, radius of action, number of tankers needed, and the actual procedure of refueling.4
Kusaka also turned his attention to the refueling question, vital to the mission. He did so because he had already gained experience along these lines and because this problem ranked number two on his priority list, second only to secrecy.5
From this meeting forward, Yamamoto’s scheme left the conceptual stage and emerged as a potential war plan. From this instant, too, Nagumo’s officers had a sense of direction, a realization of mission. Kusaka considered this so important that he broke with tradition and confided the secret even to the fleet paymaster and medical officer. The chief of staff believed that the First Air Fleet eventually might need their technical skills, and they would be able to prevent any possible security leaks in their respective domains.6
Immediately after Kusaka’s briefing the study group set to work in a close race with time. Its report would form the basis for the First Air Fleet’s operational plan and discussions for presentation at the war games which loomed in the near future. The group members labored so well that within a few days they had a general report ready for Kusaka.7
Genda devoted most of his effort to preparing a study of proposed routes from Japan to Pearl Harbor. The Japanese had to select the one which would reduce to an absolute minimum the danger of detection by American forces. Ever since they heard about the Pearl Harbor enterprise, Nagumo and Kusaka had concerned themselves deeply with this question, and Genda had mulled over the various possible approaches to Hawaii throughout the spring and summer.8
Long before he started his staff study for Kusaka, he had settled in his own mind what passage the task force should follow, but he had no power of decision. As a good staff officer he had to make an intensive survey of all the possibilities, setting forth exhaustively and impartially the factors for and against each one. So he developed a staff study which presented for Kusaka’s evaluation and Nagumo’s decision three routes: southern, central, and northern.9
For the southern route Genda suggested two prospective points of departure—Saeki in northern Kyushu and Hashirajima in the Inland Sea. From either of these anchorages the task force would proceed piecemeal to its rendezvous—Wotje in the Marshall Islands. Genda picked Wotje because it offered a suitable anchorage in the Mandates relatively near Pearl Harbor. Being able to refuel approximately halfway to the target, the carriers could complete the voyage without a transfusion from the tankers if necessary.10
Genda considered two possible routes from Wotje to Pearl Harbor. The first he called the “direct approach.” Steaming out of the Marshalls in a northeasterly direction, the task force would sweep south and east of Johnston Island. Then it would angle northward until it reached the attack launch point some 200 or 250 miles south of Pearl Harbor. This approach had several advantages: a minimal fuel problem; relatively calm seas; and proximity to Japanese bases, which would provide an important margin of safety in case of emergencies. But Genda saw disadvantages as well. First of all, those sundrenched skies offered no cover for the task force. Even more dangerous, Kimmel’s fleet used this sea space southeast of Hawaii for training. Only by fantastic good fortune could the Japanese evade both the patrols and an American exercise.
Genda’s second route from Wotje to Pearl Harbor had the task force moving in a line between Howland, Baker, and the Phoenix islands on the south and Kingman Reef, Palmyra, and Christmas Island on the north. Some 400 miles southeast of Christmas Island, Nagumo would swing his ships northward. When he had reached a point about 600 miles southeast of Mauna Loa on Hawaii, Nagumo would proceed northwest until approximately 200 miles southeast of Oahu and launch.
Genda decided that this alternate route contained all the disadvantages of the first plus a serious refueling problem. Then, too, if the Americans spotted the Japanese fleet, Nagumo would be trapped—Kimmel’s ships cutting him off from retreat to the Marshalls, Short’s defenses in front of him, and nothing on his starboard flank but United States-dominated ocean.
This route had only one thing to be said for it: The United States Navy would consider a Japanese attack against Hawaii from southeast of Oahu about as remote a possibility as hail in hell. But while Genda insisted on surprise, there were limits!11
Next, he turned his attention to a central route, selecting as departure points Yokosuka and, again, Hashirajima. After due study and deliberation Genda chose as rendezvous point Chichi-Jima, some 700 miles southeast of Tokyo, a far from ideal spot. Its roadstead could not hold the entire task force, and it was particularly vulnerable to U.S. submarine surveillance.12
Thence Genda theoretically sent Nagumo’s ships northeastward to about 500 miles north of Midway. From Midway he shifted the task force to a southerly course, which it would hold until “the extreme danger zone”—the area about 750 miles north of Oahu. From that point Nagumo would head directly south and, when within striking distance, launch his aircraft.
Genda discovered few advantages in this central approach. True, it steered a happy medium between the dangerous exposure of the southern route and the stormy seas of a more northerly one. But beyond that, troubles would mount: the inadequate rendezvous point; the danger of American submarine, surface, and air patrols in the Midway area; the flanking of the Hawaiian chain to the north. He could not recommend this course, nor did anyone else when it came up for discussion.
From the first, Genda inclined toward a northern route.13 Any of the Inland Sea anchorages could serve as the port of departure, although selecting the final point of rendezvous posed a difficult problem. He had a number of possibilities to choose from, but none fully satisfied him. After some study Genda and Oishi agreed that not one of the places Genda had suggested was suitable from the standpoint of security.
Temporarily shelving the rendezvous problem, Genda worked on a route through the northern Pacific which provided tolerable weather conditions as well as excellent opportunities for concealment. The bulk of merchant ships shuttling between the United States or Canada and Japan or the Soviet Union sailed farther north than Genda’s proposed passage. Thus, this location offered the least possibility of detection.
Again Genda offered two alternatives. The first specified departure due east from Hokkaido along 42° north latitude; once about 1,000 miles dead north of Oahu, the task force would turn sharply south for the target area. The second was rather more elaborate: Nagumo’s ships would follow the first track until due north of Oahu; then they would continue southeast until they had reached a point 800 or 900 miles northeast of Pearl Harbor, where the task force would shift course southwest and approach Pearl Harbor on a straight line.
This suggestion appealed to Genda for a number of reasons. He proceeded on the premise that air and surface patrols out of Oahu would give scant attention to the northeast. A wide swing eastward would probably evade discovery from Oahu and still dodge patrols originating on the West Coast of the United States. Then, too, Nagumo’s ships would lie across the path of American reinforcements from the United States.
The weakness in this route lay in the chance of discovery by commercial planes and vessels plying between the West Coast and Hawaii. Eventually Genda would discard this passage in favor of a simpler one, but at the time he believed that if the Japanese should accept his suggestion to make Operation Hawaii an all-out project complete with landing party, the task force should use the northeastern approach.
Sasabe, Nagumo’s navigation officer, worked on the same aspect of the operation;14 so did Watanabe on Yamamoto’s staff. Each investigated such problems as weather, visibility, condition of the sea, and shipping routes in the northern Pacific.15
When Genda took this report to Kusaka, he found that the chief of staff approved a northern route. Kusaka fully realized the problems inherent in the rough seas, especially the formidable task of refueling. But in his judgment these weighed lightly against the ultimate consideration of surprise.
The inclement weather that usually lowered over the area north of Pearl Harbor in the late autumn and winter presented the Japanese with two distinct advantages: “It reduced the possibility of detection, and it made patrol activity by the American Navy more difficult.” And thanks to Yoshikawa’s reports from Honolulu, the Japanese Navy knew that U.S. patrols “were weakest in the area north of Pearl Harbor.” Nevertheless, Kusaka expected the Americans to patrol in a full circle around Oahu; the problem therefore was “to maneuver through the patrol lines and press the sudden attack.”16
Genda now had to embark on a very difficult task—that of selling his choice to Nagumo. The admiral and his air officer had disagreed over routes from the outset. Nagumo particularly disliked the northern course. How could his tankers possibly refuel a fleet in the pitching waters and foul weather that the northern Pacific promised in late autumn? How could the ships navigate properly, keep formation, and preserve the task force as an integrated fighting unit? He envisaged his destroyers wallowing helplessly in mountainous seas; he might even have to send them home, thus depriving himself of priceless antisubmarine protection.
But Genda continued to preach the northern route to Nagumo with evangelical zeal, trying to convince his chief that the best chance for catching the enemy unawares would be to approach from an unexpected direction. “If you think the northern route is bad,” he argued, “then you must remember the American admirals will think the same.”17
He treated the dubious Nagumo to many a pep talk, reminding him of outstanding examples in Japanese history in which resourceful commanders had surprised and defeated a foe against impressive odds. And he tried to assure Nagumo that wise planning and intensive training could overcome the disadvantages of the northern route—handicaps which Genda readily admitted.18
On this point a split in orientation existed between Nagumo and Genda. To the latter, surprise was the overriding factor. The Japanese must subordinate everything to the absolute necessity for catching the enemy off guard. For his part, Nagumo had virtually written off any chance of achieving complete surprise. He strongly believed that American patrols would discover the task force no matter what course it took. Therefore, Nagumo preferred to select a route which would enable the First Air Fleet to reach the target area in good condition and to function with maximum striking power. So he held tenaciously to the shorter southern route. Its calm seas and Japanese bases in the Marshall Islands, in his opinion, more than compensated for the route’s dangers.19
While the First Air Fleet staff wrestled with these assignments, Genda received a welcome reinforcement—an assistant air officer. Sharp, flexible-minded Lieutenant Commander Chuichi Yoshioka was a distant relative of Nagumo’s. He enjoyed a reputation as one of Japan’s most experienced and able aviators. He was not an aggressive man, and Fuchida believed he was more at home in a staff assignment than as a warrior.20 But when Yoshioka joined Akagi at the age of thirty-two, he already had several thousand hours of flight time to his credit, much of it in combat missions over China and the Burma Road. Yoshioka struck an exotic note in the Japanese Navy, being a Christian—a lifelong Methodist, whose five children attended Sunday school regularly.21
During the tough, exacting weeks of intensive planning and training ahead Yoshioka became Genda’s alter ego because of all of Nagumo’s staff, only these two officers truly understood the meaning and potentialities of naval aviation. He soon found that while Genda was “a tower of strength to both Kusaka and Nagumo,” the two admirals “literally feared some of Genda’s ideas” as overly radical.
Yoshioka was not particularly surprised when Genda told him about Operation Hawaii in early September, but he was shocked to learn that “Japan was really going to war with the United States.” He did not immediately share Genda’s enthusiasm for the Pearl Harbor scheme. “The plan might look good on paper, and make quite an impression in table maneuvers, but to carry out such an operation in the face of sharp enemy opposition was quite a different matter,” he reflected after the war.22
A number of other changes took place in the First Air Fleet’s personnel in early September. Of immediate interest to Genda and particularly to Fuchida, hard at work training for he still knew not what, Lieutenant Commander Shigekazu Shimazaki joined Zuikaku (which was not yet ready for action) as flight commander on September 10.
Shimazaki was one of Japan’s most versatile fliers, an expert on all types of bombing—dive, horizontal, and torpedo. “A man of iron nerves, never upset or excited,” said Genda. “He was the Admiral Togo type—the ideal Oriental hero variety.” Although not as clever as Fuchida, he had a level head. Once he took off, his own bloodstream seemed to flow through the plane, and he was at his best under fire.23
Although somewhat inarticulate, this big man had a good sense of humor, a knack for leadership, and he was the solid, practical type. Fuchida liked his new assistant very much and came to depend upon him in the days to come.24
The September personnel shifts touched even Yamamoto’s own official family. Ito, who preceded Ugaki as the Combined Fleet’s chief of staff, transferred to Tokyo to take up his new duties as Nagano’s vice chief. It was exceedingly rare for a rear admiral to be selected for this important post. Nagano had specifically requested him as his deputy. Fukudome characterized Ito as “a steady man, a thorough worker and deep thinker. He was considered an excellent officer with a good future. He lacked only one thing—aggressiveness and a fighting spirit.”25 Thus, as of September 1, two of Yamamoto’s former chiefs of staff, both of whom knew about Pearl Harbor—Fukudome and Ito—held key positions under Nagano.
Whatever the differences—and they were many and serious—remaining between the Naval General Staff and the Combined Fleet, the torrent of events was pulling the two organizations ever closer to each other and to the maelstrom of war. On August 15 the Navy had issued orders to prepare for possible conflict with “the beginning of October as the target date for the completion of preparations.” Upon receipt of these instructions, at the end of August the Combined Fleet discontinued the training and operations then under way in China and “instructed fast preparations within about a month.” Then, on September 1, Yamamoto’s headquarters issued orders for “complete wartime organization.”26 In addition, sometime in August or early September the Naval General Staff directed that a model of Oahu be constructed, probably at the request of the Combined Fleet.27
So, however much it officially disapproved of Yamamoto’s plan, Nagano’s branch of the service continued to cooperate with the Combined Fleet in such practical matters as moving up the war games and preparing training aids for Operation Hawaii. All these activities took place before the imperial conference of September 6 and before Konoye and Grew met that evening for their historic dinner engagement.