In early April 1941 Yamamoto sat closeted in his cabin aboard Mutsu—Nagato was undergoing overhaul—with two of his key officers, Captain Kameto Kuroshima and Commander Yasuji Watanabe. Several weeks had gone by since Onishi first submitted his and Genda’s draft to Yamamoto, and Kuroshima and Watanabe already knew the general trends of Yamamoto’s thinking. Kuroshima, in particular, was no stranger to his ideas. Several times during 1940 Yamamoto had discussed with him the strategy Japan should follow in case of conflict with the United States. As the weaker nation Japan could not fight a defensive war; its only chance would be to seize the initiative and strike first.1
Yamamoto had put his staff to studying the Pearl Harbor plan no later than January. About the middle of that month Kuroshima directed Commander Akira Sasaki, Yamamoto’s air officer, to examine three possible alternatives. The first assumed that the Americans would be strictly on guard. In that case the Japanese would approach within approximately 350 miles of the target and bomb only American carriers, with fighters guiding the bombers. The second called for penetration to some 200 miles and use of all the Japanese aircraft in the attack. The third was a one-way attack employing only bombers, with submarines hovering nearby to rescue the crews.2
Sasaki realized, of course, that the plan would be risky and dangerous, but he believed if the worse came to the worst, it might be Japan’s only way out. An Eta Jima and Kasumigaura graduate, Sasaki had spent about two years in the United States as an assistant naval attaché, beginning in 1931. Before coming to Nagato, he had been staff officer for air of the China Area Fleet located at Shanghai.3
Sometime in late March Fukudome had shown Kuroshima the Onishi-Genda draft, and Watanabe saw it a few moments later. Fukudome and Kuroshima agreed that if war with the United States seemed likely, they should submit the project to the Naval General Staff. But for the time being they should study it carefully aboard Nagato. Sasaki also saw the draft at that time. It was then that the document’s assessment of the difficulties in carrying out a torpedo strike apparently discouraged Yamamoto. He is reported to have remarked, “Since we cannot use a torpedo attack because of the shallowness of the water, we cannot expect to obtain the results we desire. Therefore, we probably have no choice but to give up the air attack operation.” But Yamamoto was not the type to abandon any venture until he had thoroughly explored all avenues. Thus, on this April day once more he broached the subject to Kuroshima and Watanabe.4
Kuroshima had been with Yamamoto since the autumn of 1939. Primarily a gunnery officer, he had spent much time at sea, had graduated from the Naval Staff College, and had also taught there. Now he served as Yamamoto’s senior staff officer. Kuroshima’s actual duties consisted mainly of overall planning, and his position was somewhat like that of Kimmel’s Soc McMorris. However, the ranking member of a Japanese naval staff was called the senior staff officer. Kuroshima’s taut cheekbones and pale prophet’s face gave him such an ascetic appearance that his colleagues called him Ganji—the Japanese form of Gandhi.
Although the Japan of his day set a premium on conformity, Kuroshima was eccentric to the point of weirdness. Even his name was unusual. Kameto means “tortoise man.” It suited Kuroshima well enough, for he liked to retreat into his shell when working on a problem. He would lock himself in his cabin, draw the shades, and sit in the dark with his head buried in his hands. When an idea struck him, he would turn on the light and begin to scribble frantically, shedding papers all over the floor and smoking heavily. He even ate his meals in his cabin, letting dirty dishes and glasses full of cigarette butts accumulate until his colleagues would protest and order the cabin cleaned up.5
When Kuroshima emerged from these solitary sessions, he had the problem thought through to the smallest detail, at least to his own satisfaction, and could dictate a staff study word for word without consulting notes. Nevertheless, he sometimes lost his grip on reality and produced some far-out ideas. Yamamoto knew exactly how to sift a Kuroshima plan and toss out the chaff. When someone asked him why he kept such a strange officer on his staff, he replied, “Who else but me could use Kuroshima?” No man on the Combined Fleet staff would work harder on the Pearl Harbor plan or support it more enthusiastically than Kuroshima. In fact, Genda thought that the senior staff officer very likely knew of the plan even before he did. Sasaki, too, believed that in view of Yamamoto’s full confidence in his staff “it was almost inconceivable that he would consult anyone on the outside concerning such an important operation without first considering it with such members of his staff as Fukudome, chief of staff; Kuroshima, senior staff officer; and myself, staff officer for air.”6
If Kuroshima had a crony, it was Watanabe. This solidly built man, almost six feet tall, exuded an atmosphere of expansive maleness and simple, earthly virtues. Indianlike cheekbones lent force to his oblong face with its expressive dark eyes and wide mouth full of large white teeth. His sunny optimism freshened Kuroshima’s dark melancholy. A head crammed with ideas, the strength to cut his way swiftly through a pile of work, and the discipline to follow up on his assignments made Watanabe the ideal staff officer.
Yamamoto had a soft spot for Watanabe and treated him like a son. The two often played chess (shogi) or cards together. Indeed, Yamamoto considered their chess sessions almost in the line of duty, believing that the game cleared his head and kept him alert.7 Watanabe repaid his chief’s kindness with a full measure of devotion. Indeed, Yamamoto’s entire staff resembled that of Kimmel in its prickly allegiance, its exclusive, excluding pride.
In entrusting Kuroshima and Watanabe with detailed work on the Pearl Harbor plan, Yamamoto embarked on his own initiative. In wartime the Commander in Chief of the Combined Fleet had the responsibility and authority to draft an operational plan within the framework of any mission assigned to him from the High Command. In peacetime, however, he was not supposed to work on such a plan because of the security risk involved and also because the Naval General Staff preferred that he concentrate all his efforts on training. The Naval General Staff drafted the annual plan. In case of emergency, one of its officers brought the plan to Combined Fleet Headquarters.8
But in view of the immense importance of the timing of the Pearl Harbor attack—it must start the war, not follow a declaration—Yamamoto could not wait for the mills of the naval gods to grind in Tokyo. Once war had been declared, he would have lost the imperative of surprise, the one basic element upon which his air strike depended.
So within a few days Kuroshima divided Yamamoto’s staff into four preliminary study groups: (1) Operations and Supply; (2) Communications and Information; (3) Navigation and Meteorological Conditions; and (4) Air and Submarine Attack.9 Thus, the ring of knowledge expanded to include Lieutenant Commander Yushiro Wada, communications officer, and Commander Shigeru Nagata, navigation officer.
Commander Takayasa Arima also joined the inner circle. Although one of the youngest members of Yamamoto’s official family, he carried weight by virtue of his assignment as submarine officer. The Japanese Navy took great pride in its submarines and expected much of them, having concentrated heavily in this area of sea warfare as a result of the posttreaty limitation on surface vessels. Arima had little submarine experience, being a torpedoman by training, but he was ready, willing, and able to learn. He had studied for two years in the United States—one at Johns Hopkins and another at Yale.
When Kuroshima first spoke to Arima about Yamamoto’s plan, Arima felt clouds of pessimism drift across his mind. An air attack on Pearl Harbor? Impossible! he thought. But the idea grew on him. Soon he accepted the plan as “the only way to defend and secure the extended line of the Greater East Asia Co-Prosperity Sphere.”10 In the months to come Arima would work tirelessly, maintaining close liaison with the Sixth Fleet (Submarines) and with the Naval General Staff.
The plan’s element of the unexpected had appealed to Sasaki from the first. During the development of the project Sasaki cooperated closely with Genda and became more or less the Combined Fleet’s liaison with the First Air Fleet, soon to be activated. This suited his personality as well as his training because his assured and pleasing manner permitted him to establish an easy rapport. At the same time he could keep his own counsel.
Sasaki assures us that by early April 1941 most of the operations officers of the Combined Fleet staff knew about the Pearl Harbor attack plan. This included his own assistant for air, Lieutenant Commander Kaneo Inoguchi. Sasaki always suspected that Kuroshima might have originally suggested the idea to Yamamoto; however, Kuroshima consistently denied this.11
During this early planning period an intriguing question arose between Yamamoto and “three or four staff members”: the possibility of occupying Hawaii in connection with the air attack. Someone suggested that because about half the U.S. Navy was in Hawaii, if they could take these men prisoner, the recovery of American naval strength would be difficult because of the time needed to train officers. This idea never progressed beyond informal chitchat, although the notion of running up the Rising Sun over Hawaii intrigued Watanabe for months.12
Thus, by mid-April Yamamoto had moved the Pearl Harbor project into command channels and established it as an authorized subject of staff study. What followed seemed only logical.
On April 10 the Navy took a momentous step which signaled a revolution in its strategic thinking. On that day it organized the First Air Fleet, bringing together in one operational unit the First Carrier Division (Akagi and Kaga), the Second Carrier Division (Soryu and Hiryu), and the Fourth Carrier Division (Ryujo). In addition, the First and Second Carrier divisions each had four destroyers assigned, and Ryujo two. Ryujo transferred elsewhere in the summer of 1941 and played no part in the Pearl Harbor drama; her small size and comparatively slow speed made it impractical to use her as an integral part of the First Air Fleet especially because all her fighters were the old Type 96, not Zeros. The organization included her only to assist in coordinated training.
With this move the Japanese Navy formed the nucleus of a potential aerial striking force capable of massing well over 200 planes against a given target. For at least five years Genda had advocated such an air fleet, the carriers concentrated as a unit to achieve maximum offensive power, with other vessels acting as defensive escorts.13
Despite his personal sympathy with naval aviation, Yamamoto had hesitated to approve the formation of the First Air Fleet for some time. It was an advanced concept, involving the sort of physical, mental, and even spiritual shake-up to which a commander cannot subject his organization without careful thought. Ozawa brought the issue to a head early in 1940, when he commanded the First Carrier Division. Four months of service with Japan’s two biggest carriers convinced Ozawa that it would be possible to launch powerful air strikes only if the flattops were organized under one command. According to Captain Sadamu Sanagi, air officer on Yamamoto’s staff before Sasaki, one of the burning questions among airmen in the Combined Fleet was: “How can air power be used most effectively?” And he remarked, “Ozawa had spent most of his naval life at sea and was by all odds the most vigorous exponent of uniting the carriers as a striking force.”
But Ozawa ran into opposition. One of the top brass who resisted his scheme was Vice Admiral Mineichi Koga, Commander in Chief of the Second Fleet, where Soryu and Hiryu had their home. Koga believed in the battleship as devotedly as he did in the cause of Japan. He feared that with the transfer of the flattops from their respective fleets, the latter would lose their protective air cover.
Twice Ozawa discussed his idea with Yamamoto, and twice his chief turned it down, sensing that the time was not yet ripe. But Ozawa was certain that in his concept lay the key to Japanese naval supremacy. Being as stubbornly audacious as his superior, he formally submitted his plan to Yamamoto in April 1940. At the same time he went a step further and presented his recommendation to the Naval General Staff and the Navy Ministry. Yamamoto blew up when he learned that Ozawa had bypassed him. Of course, Ozawa knew that Yamamoto’s anger arose from the breach of protocol and had nothing to do with the carrier control plan, which his chief favored at heart, and the two officers remained good friends.
The Navy discussed Ozawa’s plan during the summer and autumn of 1940. At last, in December, Yamamoto agreed, and soon everyone else fell into line. Yamamoto came around finally because he saw that such an organization was the only way to achieve maximum striking power from Japan’s carriers.14 With the swift improvement in aircraft capabilities, it had become increasingly possible that a decisive air battle would precede any final naval engagement such as the Great All-Out Battle. Then, too, the concentration of carriers offered advantages for training.15
Even before the official organization of the First Air Fleet, the Japanese had practiced with a mass concentration of carriers. In accordance with Genda’s theory, they had combined Kaga, Soryu, and Hiryu into a unit temporarily for training in early 1941. (Akagi was under repairs at the time.) This method proved very effective operationally, but some “bugs” soon appeared in the organization, for it became obvious that merely combining the existing carrier divisions created command difficulties. A temporary commander had to be selected, the airmen had to become familiar with his tactics, and the training methods of both carrier divisions had to be aligned.
This experimental concentration drove home forcefully the need for a permanent unified carrier command. Moreover, Yamamoto was becoming more and more intent upon launching his carrier strike at Pearl Harbor. The Commander in Chief signaled “Go!” Barely four months later the First Air Fleet became a reality. Genda understood very well that he could not credit himself or his devoted band of naval aviation champions with bringing about “this revolutionary change” in the Japanese fleet organization, which “marked an epoch-making progress in the field of naval strategy and tactics. . . .” He generously gave full credit to Yamamoto’s farsighted belief in air power.16
Other shake-ups occurred at high level in the Japanese Navy on the same day that the First Air Fleet came into being. Admiral Osami Nagano became chief of the Naval General Staff. A full admiral since March 1, 1934, he had held many important posts, including vice chief of the General Staff, navy minister, and Commander in Chief of the Combined Fleet. Thus he knew all three major sections of the Navy by personal experience at the highest level. Like Yamamoto, he had studied English at Harvard and served as naval attaché in Washington. All told, he had spent five years in the United States and considered New York City his second home.
At sixty-two Nagano was the oldest officer on the Navy’s active list. He had lost much of the strength and drive of youth. “He was not a forceful character or the type to lead his nation at war,” one of his section chiefs summed up.17 In reading reports of Nagano’s remarks in various high-level conferences, one has the impression that he increased in belligerence as 1941 progressed, either falling under Army influence or growing in self-confidence. But his thorough, slow-moving mind was no match for the quick, sharp intelligence of Yamamoto. Such then was the admiral who as chief of the Naval General Staff wielded the power of life or death over any operational plan.
Also on April 10 Yamamoto gave up his trusty chief of staff, Fukudome, to Nagano’s headquarters as chief of the First Bureau. In that capacity Fukudome headed the nerve center of the Naval General Staff and to a certain extent of the entire Navy. Its personnel originated, discussed, studied, perfected, and constantly reviewed operational plans. In exchange for Fukudome, Yamamoto received Rear Admiral Seiichi Ito, an officer with an excellent background, including language study in the United States, but of a conservative bent of mind. A good public relations type, Ito got on well with both superiors and subordinates. Naturally he learned about the Pearl Harbor scheme shortly after boarding Nagato. From all reports he did not exactly applaud the notion, but as always he accepted the command decision passively and did nothing to thwart his chief.
Fukudome took with him to the Naval General Staff his personal knowledge of exactly what Yamamoto had in mind. Then, about a week or so after Fukudome had settled in Tokyo, Onishi called on him and presented him with a copy of his draft. He informed the new chief of the First Bureau that he had already briefed Yamamoto, who had instructed him to give the draft copy to Fukudome for safekeeping. He then explained the outline, and the two men discussed the project briefly. When Fukudome read the draft, he believed that the idea had made considerable progress since he first talked it over with Yamamoto in 1940 but that many serious problems remained to be solved. When Onishi left, Fukudome hastily put the document in his safe.18
Yamamoto had too much integrity to attempt to use Fukudome as his stooge in the Naval General Staff. So, late in April, he dispatched Kuroshima to Tokyo to discuss the possibilities of his plan with the Operations Section of Fukudome’s First Bureau. This was the fountainhead of all naval planning and should have initiated any scheme to attack the U.S. Pacific Fleet or for that matter any other war plan. This key organization was loaded with smart, up-and-coming young hopefuls carefully chosen for background, brains, originality, and vision to keep the Navy on its toes.
A highly gifted officer headed this section. Captain (Baron) Sadatoshi Tomioka’s record reveals a solid background of schooling and sea duty, and he had seen much of Europe. His cultivated, fastidious, and practical nature flourished particularly well in the intellectual and social climate of France, where he had studied. The complete aristocrat, Tomioka exuded the confidence and security of one who knows exactly what to do and say under any circumstances. A man of brains and common sense, he knew his job exceedingly well.
His naval training had sharpened his innate sense of responsibility until his feeling of unity with the ships had become supersensitive. But he knew the Navy’s limitations as well as its capabilities, and he therefore objected to overextension. Let Japan keep its eye on the goal: Southeast Asia. If anyone went gallivanting across the Pacific, let it be the United States. The view from Tomioka’s desk encompassed a broader scene than that from Nagato’s bridge. “The Combined Fleet could study the Pearl Harbor plan from the purely tactical and strategic point of view,” he explained, “but the Naval General Staff had to include its relations with the Army, the Cabinet, the Foreign Office, and Japan’s entire international situations.”19
According to Tomioka, Kuroshima’s visit of late April was the first he and certain of his officers learned about Pearl Harbor. To anyone accustomed to the methods of the American armed forces, it appears incredible that the chief of a section should be unaware of a plan on which one of his subordinates—Uchida—claimed to have been working. But the situation was not unheard of in the Japanese services, in which junior officers sometimes enjoyed a surprising amount of freedom.
In any case, Tomioka took this opportunity to discuss with Kuroshima the Naval General Staffs overall war plan, which had as its main objective the seizure of Southeast Asia and its rich resources. Absolutely nothing should interfere with the success of the prime mission. The Naval General Staff blueprint also featured a modified version of the Great All-Out Battle which would ensue when the U.S. Pacific Fleet sailed westward to block Japan’s southern advance. This included the dispatch of a sizable submarine force to Hawaiian waters to begin reducing the American Fleet as it crossed the Pacific.
Neither Tomioka nor Kuroshima was at all impressed with the other’s ideas. Nevertheless, Kuroshima requested that the Pearl Harbor design be included in the Naval General Staffs planning. But Tomioka believed that Yamamoto’s scheme presented an inadmissible risk and that Japan could not spare from the Southern Operation the ships which an attack on the U.S. Pacific Fleet in Pearl Harbor would require. Furthermore, he thought it operationally impossible because of the limited radius of action of Japan’s warships. He added decisively that none of the Japanese carriers had any experience in refueling on the high seas.
Tomioka could have informed Nagano of Yamamoto’s plan after Kuroshima had returned to the Combined Fleet. In fact, Kuroshima assumed Tomioka would do so. He also thought that “even from the common sense point of view Nagano should have been informed at the time.”20 But Tomioka was not the type to go rushing to Nagano with it at that stage. Nevertheless, after Onishi’s and Kuroshima’s visits to Tokyo, Yamamoto’s plan had been officially introduced to the Naval General Staff, whether the high brass liked it or not. In short, Yamamoto’s camel had its nose in Nagano’s tent.
Commander Tatsukichi Miyo, one of Tomioka’s two air experts, agreed with his chief. A man of keen, down-to-earth intelligence, Miyo was a graduate of Kasumigaura. He understood and strongly backed carrier-borne aviation, but he considered Yamamoto’s scheme “entirely out of the question.” He estimated that the Army’s air force was too weak to accomplish the mission in Southeast Asia without strong support from the Navy’s carrier-based strength. Then, too, much planning and thought remained to be done on the Southern Operation. All energies should be concentrated on the primary objective, rather than on planning attacks which seemed impossible to execute.21
Whatever opinion Miyo may have expressed to Tomioka, he had been working on at least one phase of a Pearl Harbor operation for some months, according to a reliable source. Early in January he visited the Navy Ministry and called upon an Eta Jima classmate, Commander Fumio Aiko, an authority on torpedoes. Miyo presented Aiko with a tall order—100 percent perfection in aerial torpedo results in shallow water.
Aiko blinked at his classmate from behind his thick glasses. Japan already had 70 percent efficiency. A reasonable man, Aiko considered a perfect score impossible and flatly said so. But Miyo continued to urge the point. Finally, Aiko asked, “Why do you press for a hundred percent?”
Miyo shot a quick glance around him and lowered his voice. “I will tell you a secret,” he confided. “We need this special shallow-water torpedo because the Navy has a plan to attack the U.S. Fleet in Pearl Harbor. This is an absolute secret,” he stressed.
Aiko was not in the least surprised because he more or less took it for granted that eventually Japan and the United States would fight. He had been working for some time on shallow-water torpedoes. At the fleet maneuvers held in 1939 in Saeki Bay, which featured a simulated torpedo attack, Aiko became convinced that if real missiles had been used in such a low depth of water, they would have stuck in the mud.
With this thought in mind he had done some research on his own initiative into the depths of such harbors as Manila, Singapore, Vladivostok, and Pearl Harbor. He discovered that the average was from about seventeen to twenty-five feet. Obviously, to be effective in such circumstances, the torpedo could sink no lower than twelve feet. Aiko then combined his research and his previous experience of torpedo-sinking curves into a formal report for the Aeronautical Bureau of the Navy Ministry. As a result, he was assigned to the Combined Fleet, where he remained as an instructor until December 1940, when he transferred to the Aeronautical Bureau. There he was hard at work when Miyo called upon him in January 1941.
Miyo’s insistence upon secrecy put Aiko in a difficult position because his associates would have to work in the dark. But the torpedo expert never told anyone about the Pearl Harbor mission. As a result of their conference, he wrote to the commanding officer of the Naval Air Corps at Yokosuka, directing him in the name of the navy minister to improve torpedo efficiency to 100 percent. However, because Aiko would give no reason for the order, the Yokosuka Air Corps assigned the project a low priority.22
With all three branches of the Imperial Navy involved in the Pearl Harbor venture in varying degrees, one inevitably asks: Did Yamamoto organize the First Air Fleet for the express purpose of attacking the U.S. Pacific Fleet at Pearl Harbor? The answer must be both yes and no. No because in December 1940, when he set the ball rolling, no one knew that Japan and the United States would not settle their differences by diplomacy. Nor had the cause become hopeless by April 10, 1941; Yamamoto had no intention whatsoever of starting a Japanese-American war unless he absolutely had to. Yes because, if events forced him to lead the Combined Fleet into battle with Kimmel’s ships, Yamamoto determined that he must strike that first blow, and he could not do so without the nucleus of a carrier task force in being.
Although strength is not necessarily identical with numbers, with the formation of the First Air Fleet the Japanese Navy took on greater strategic potential than the U.S. Pacific Fleet. Without the First Air Fleet, which ultimately evolved into a powerful task force, Japan could not have delivered its mass air attack on December 7, 1941.