Japan blossomed in a garden of flags. This was May 27—Navy Day, anniversary of the Battle of Tsushima. On this festive Tuesday in 1941 the Navy had something unusual to brag about: an excellent demonstration of torpedo and other bombing techniques which some sixty planes each from the First and Second Carrier divisions put on at Sukumo Bay off the coast of southwestern Shikoku.1
Captain Hideo Hiraide, the Navy’s spokesman, never at a loss for words, outdid himself in a flight of eloquence that night over Tokyo’s radio station JOAK. He asserted:
. . . the naval air force has now some 4,000 planes which have constantly been drilling themselves for special war tactics. . . .
Thus with a firm conviction and confidence, the Navy is now biding its time with full preparedness . . . to crush in a moment anyone who dares to challenge Japan.
The Imperial Japanese Navy air force . . . are now working out stratagems that will deal instantaneous death to any nation.2
One would give much to have heard Yamamoto’s comments at this point. Not only did he dislike this sort of bombast, but some of Hiraide’s remarks came so uncomfortably close to the truth that they virtually constituted a breach of security.
By the end of May Nagumo’s airmen had already been hard at work for the better part of a month. Nagumo had issued a lengthy document concerning training policy which, although undated, obviously came into being shortly after Kusaka briefed him on the Pearl Harbor project. This document established the beginning of July 1941 as the deadline by which the new organization should achieve a standard of basic training equal to that of any other in the Imperial Navy. By the end of August the First Air Fleet should have reached its “battle capacity,” ready to operate as a unit. After that time its efficiency would be further refined.
Nagumo underscored such items as surprise mass aerial attacks on enemy air bases, destruction of enemy carriers, maneuvering of the First Air Fleets flattops in battle, and coordination with land-based and submarine forces. To implement this strategy, the First Air Fleet would concentrate on such tactics as use of various types of aircraft in coordinated strikes, night torpedo attacks, air battles involving large formations, night fighter techniques, repeated attacks employing the entire air force, improvement of antiaircraft and antisubmarine measures; and methods of evading torpedoes.3
Here was a program to delight Genda and offer Kusaka the challenge of his life. The latter withdrew into Buddhistic contemplation. Suddenly he remembered Kinshicho-Oken, a form of swordplay which he had learned in childhood. By this method one pressed in near the foe, held the sword over his head, and struck downward with one fierce stroke, then returned to one’s original position. Kusaka resolved to adopt this as the model for his tactics in the First Air Fleet.4
In close teamwork with Kusaka, Genda handled “all the plans related to aviation” and also worked on studies and training concerned with “naval operations in general.” He knew the hazards of so much responsibility. “When one works on planning,” he mused, “he tends to fall into the illusion that he has become great and he is the commander of the whole thing.” Such an attitude spelled “plenty of harm.” On the other hand, Genda did not intend to become a mere paper shuffler, “not using his brain for suggestions.” He took to heart a remark of Nagumo’s—“Without the union of people working together, a Pearl Harbor attack is impossible”—and a crisp statement from one of his torpedo officers: “We want hustlers!” To Genda these “valuable principles distilled through long experience” were like the “rivet of a fan” holding the individual sticks in a workable whole.5
Meanwhile, in early June Genda launched the First Carrier Division on the initial aerial torpedo program aimed directly at carrying out Yamamoto’s plan. He scheduled the torpedo practice as the first part of the training because he believed it would be the most difficult to perfect.
Kyushu, southernmost of the four main islands of Japan, had been chosen as the setting for training.6 On its southeastern shore lies Ariake Bay, where ships of the Combined Fleet often anchored. Due west across a thick neck of land Kagoshima Bay merges into a beautiful harbor extending far inland. With a little effort of the imagination one can see a resemblance to Pearl Harbor. Stretch the fancy a bit further, and the city of Kagoshima on the northwest side of the bay becomes the Pearl Harbor shipyard. The imagination wails a protest at transforming Sakurajima, a dormant volcano about 4,000 feet high which juts far out into the water from the opposite side of the bay, into Ford Island. For the latter is flat as a pancake, though the location is roughly similar.
In this subtropical setting somewhat evocative of Hawaii the torpedomen of the First Carrier Division began their special training. All that summer and autumn so many planes screamed over Kagoshima that the city itself seemed to rock on the threshold of adventure.
Here we find another of those strange interweavings of threads between Japanese and American thinking in the days before Pearl Harbor. On June 13, just about the time Genda’s torpedomen were coming to grips with their problems, Rear Admiral Royal E. Ingersoll, Stark’s deputy, sent a memorandum to the commandants of all naval districts with copies to Kimmel and others. The document reminded its addressees that in the past a minimum depth of seventy-five feet had been assumed necessary for successful aerial torpedo strikes. Then it went on:
. . . Recent developments have shown that United States and British torpedoes may be dropped from planes at heights of as much as three hundred feet, and in some cases make initial dives of considerably less than 75 feet, and make excellent runs. Hence . . . it can not be assumed that any capital ship or other valuable vessel is safe at anchor from this type of attack if surrounded by water at a sufficient distance to permit an attack to be developed and a sufficient run to arm the torpedo.
3. While no minimum depth of water in which naval vessels may be anchored can arbitrarily be assumed as providing safety for torpedo plane attack, it may be assumed that depth of water will be one of the factors considered by any attacking force, and an attack in relatively deep water (10 fathoms or more) is more likely.
4. As a matter of information the torpedoes launched by the British at Taranto were, in general, in thirteen to fifteen fathoms of water, although several torpedoes may have been launched in eleven or twelve fathoms.7
Kimmel gave this memorandum careful consideration, but he still did not believe that “aerial torpedoes could run in Pearl Harbor.”8 Its waters were too shallow—an average of about forty feet.
At this particular time Genda most reluctantly had to agree with Kimmel. But Genda never abandoned his vision of aerial torpedoes with their highly destructive capability slashing into the flanks of Kimmel’s ships. The Japanese would just have to solve the many problems connected with this tactic to make the operation the success of which Genda dreamed.
Since 1933 the Japanese had been leaders in aerial torpedo techniques, launching from altitudes of slightly over 300 feet at relatively high speed. Nevertheless, torpedoes dropped under such conditions dived into the water anywhere from 100 to 300 feet, then shot up sharply, sometimes breaking surface. This resemblance to a playful porpoise instead of a deadly shark was caused by an ineffective “up” rudder. On the other hand, some torpedoes ran too deeply, a few even passing under the target vessel. To correct these defects, the Japanese tried reducing the torpedo speed, but this softened its impact. Thus, they had to minimize depth of run before the aerial torpedo could be a truly efficient weapon of naval warfare.9
In mid-1939 the Japanese used a large wooden fin attached to the torpedo as a stabilizer. This broke off as the missile hit the water. In experiments at Yokosuka Naval Base, an additional wooden plate affixed to the fin at a slight angle produced promising results. By February 1940 the experimenters had cut the depth of the torpedo’s initial plunge to about 60 feet or less. Seventy percent of these missiles ran at approximately 40 feet when launched from a height of less than 100 feet at an airspeed below 150 knots. These experiments brought to light various defects which would require modification of the torpedo itself.10
When, in January 1941, Miyo of the Naval General Staff asked Aiko to settle the torpedo issue once and for all, the latter turned the project over to Yokosuka. He also arranged that the Navy Ministry should form a committee with the chief of the Aeronautical Research Department as its chairman to stimulate the study and testing.11 But the Yokosuka experiments did not progress well because the researchers could not control the axis spin of the torpedo.12 These experiments were under way when Genda and his airmen began to practice for a maximum torpedo sinkage of ten meters—about thirty-three feet.
None of them knew that Genda demanded this seemingly impossible feat because of Pearl Harbor’s shallow waters. They attempted a test run, using only two planes armed with one torpedo each. These aircraft flew at the revolutionary altitude of only forty feet. In this tryout one of the torpedoes worked well, sinking to the desired level, but the other went much deeper.13 Almost a success—but “almost” never satisfied Genda.
At first, experimental runs hinted that the depth of torpedo sinkage was related directly to the altitude of the plane—that is, forty feet high equaled forty feet deep. However, further tests proved that no such relationship actually existed. Another problem arose during these tests—maneuverability. Pearl Harbor would offer many obstacles, and the torpedo planes were difficult to maneuver under the best of circumstances. And the training circumstances were far from the best. The torpedomen had to practice shallow-water techniques from a dangerously low altitude immediately after swooping to the target through projecting smokestacks and buildings rimming Kagoshima Bay. Moreover, they had to learn how to attack battleships probably protected by antitorpedo nets.14 Genda’s daring fliers could not help wondering why the Navy set them practicing such complicated antics.
Horizontal bombing gave Genda almost as many headaches as torpedo tactics. The Japanese Navy’s record in high-level bombing was so poor that as early as March 1941, even before the formation of the First Air Fleet, Genda almost gave up. The Navy had figured that in surface battle, twelve to sixteen direct hits from big guns could sink a ship. To secure the same results by horizontal bombing would require the total striking power of six Akagi-class carriers. But the same number of planes armed with aerial torpedoes could easily sink more than ten capital ships. The First Carrier Division therefore recommended that “the Attack Force of the aircraft carrier should abolish horizontal bombing, and concentrate on the training of torpedo and dive bombers.” But neither the Combined Fleet nor the powers-that-be in Tokyo agreed because they had the technique under special study.15
Tests had developed that a minimum weight of 800 kilograms—almost a ton—would be necessary to destroy a battleship, while 500 kilograms would suffice for a carrier, if the bombs were released from an altitude of about 10,000 to 12,000 feet. But a shortage of the special steel required precluded the stocking of such bombs. Further researches revealed that the 40-centimeter (16-inch) shells used by battleships of the Nagato class could be modified into bombs of about 800 kilograms, and arrangements were made accordingly.
The Japanese Navy wanted to use armor plate of similar quality to that employed by the U.S. Navy for experiments. So early in 1941 it set up a twenty-square-meter plate of German steel at the Kashima bombing range southeast of Kasumigaura and turned loose skilled crews from the Yokosuka Air Corps to try out the modified shells. These tests proved that in its original shape the missile little more than dented the steel plates, but that shaving off the shoulder streamlined it enough for effective results. The tests further showed a minimum altitude of 12,000 feet to be required.
Other trials at the Kamegakubi experimental firing range at the Kure Naval Base determined such factors as the new bomb’s power, penetration, and fuse time.16 The bomb, designated Type 99-No. 80-3, was a huge missile of 796.9 kilograms with 22.8 kilograms of explosives. Everything seemed to be going fine when production hit a snag. As late as mid-September 1941 only 150 bombs had come off the assembly line.17
With the formation of the First Air Fleet on April 10, Akagi had received a new flier—a graduate of the bombing course at Yokosuka, Lieutenant Izumi Furukawa. This handsome young man “was a central figure among bombing experts.”18 A prime favorite of Genda’s, Furukawa exuded energy, drive, and imagination. Though a severe taskmaster, he had the gift of imparting unsparingly the best of himself to those under him.19 When he arrived in Kyushu, he had not the least idea where the training would lead him, although of course, he joined Nagumo’s fur-helmeted fliers aboard Akagi “with some deep determination in mind.”20
Furukawa took over Akagi’s horizontal bombers and within twenty days had wrought a virtual miracle. Near the end of April, as the flagship plowed her way toward Kyushu, his men practiced against the old battlewagon Settsu, long since demoted to the rank of target ship.21 Then and for some time later, the horizontal bombers used a nine-plane formation, consisting of three planes in the lead, with two three-aircraft units in the rear, to port and starboard respectively. Because all the planes were equidistant, this produced a flight in the form of an inverted V, looking something like this:
At its very first trial the Akagi unit, attacking Settsu from about 10,000 feet, scored four direct hits in nine tries. When Genda heard this, he thought Lady Luck had been working overtime. But a second and third session that day “resulted in three to five hits each time.” What is more, a report from Yokosuka informed Genda that practice held there the same day had produced “results not inferior” to Furukawa’s.
When Furukawa returned from his practice session, Genda pounced on him. “I wonder what explains this performance?” he asked.
“The biggest factor is the pilot,” Furukawa explained. “In the past, bombing was handled by bombardiers, and the pilot was nothing but a driver. We can’t expect good bombing with such a setup. We found that piloting is a big factor in accurate bombing.”23
Furukawa’s record not only restored the Navy’s faith in horizontal bombing but held out high hopes for the future. If the difficulties in torpedo technique could not be resolved, the Japanese would have to rely on dive bombing to carry out a projected Pearl Harbor attack, but this method could not destroy capital ships. As long as horizontal bombing continued at a dismal 10 percent or less accuracy, they could not hope to achieve “the chief objective” of disabling the U.S. Pacific Fleet for six months. But the story would be very different if the high-level bombing program could produce such results as those of the Akagi unit.24
Another major reason for Japan’s poor record in horizontal bombing was the lack of an instrument anywhere near as effective as the Norden bombsight possessed by the Americans.25 The Japanese used a revised German Boyco bombsight, but its accuracy depended to a large extent on the skill of the pilot and bombardier.26 For this reason, the Yokosuka Air Corps hoped to obtain better results by training skilled bombardiers picked from the spread of the Navy, each teamed with a pilot into a permanent unit. This duet would work together until it functioned almost as one man. The First Air Fleet quickly picked up this methodology and placed one of these specially trained teams in the lead horizontal bombing planes. Each of these teams would head a formation to inundate the target with a rain of bombs dropped simultaneously in the hope that such a heavy concentration would produce results, if only through the laws of probability.27
Genda credited the upsurge in accuracy not only to Furukawa’s inspired leadership but to the work of one of these special teams. This consisted of two cheerful, eager chief petty officers, Akira Watanabe and Yanosuke Aso, an unusually diligent and persistent pair.28 In later bombing contests they always carried off first prize. Watanabe, the pilot, strikingly demonstrated Furukawa’s dictum that a pilot should be more than a chauffeur. He checked out his plane personally instead of leaving this task to the ground crew. He knew exactly how he wanted his instruments set, and woe betide anyone who touched them; he also studied precisely the “change in balance and stability of the aircraft resulting from consumption of fuel.”29 From such meticulous methods came the delicate adjustment to aerial conditions, almost by the minute, which enabled Watanabe and Aso to achieve early results of 33⅓ percent accuracy.30 If that seems unimpressive, one must remember that in the very recent past 10 percent had been the best Japan’s horizontal bombers could attain.
Fighters also trained hard in this early period. Communications in particular posed a problem. Before 1941 the Japanese Navy had never sent a fighter unit more than 100 miles from its home base or carrier, and the radiotelephone connection worked only for that distance. Now they planned to dispatch Zeros against a target 250 to 300 miles from the carriers, and at this space they had to use Morse code. So throughout the summer the Navy communications people had to train fighter pilots in this skill.31
In mid-June 1941 Onishi, Sasaki from the Combined Fleet staff, and Genda visited the Operations Section of the Naval General Staff. There they conferred among others with Miyo, Commander Sadamu Sanagi, and Commander Shigenori Kami.32 A very bright and practical-minded officer, Kami had general charge of “war-preparation and operational plans.”33 Sanagi, sharp and shrewd, had served in the United States as assistant naval attaché and had traveled in England, France, Germany, and Italy to study aviation.
The delegation made a vigorous pitch for the adoption of the Pearl Harbor project as a part of Japan’s overall strategy. In spite of their enthusiasm, Kami informed them only that the First Bureau would examine Yamamoto’s proposal. However, Tomioka’s section was to continue to study “simultaneous operations against several countries,” and the plan on which it worked “did not incorporate the operation against Hawaii because it was considered too adventurous.”34 But the conferees indulged in some tactical discussions about the proposed Pearl Harbor attack. Sasaki and Uchida insisted that battleships should be the prime targets; Genda and Kami were just as forceful that carriers and land-based aircraft must receive top priority. After the meeting Tomioka gave Genda Onishi’s report which he had worked out for Yamamoto. Genda took it back to Akagi and never showed it to anyone else.35
Early in June Genda recommended to Nagumo that all high-level bombing leaders go to Kagoshima Naval Airfield to train as Watanabe and Aso had done. Accordingly the sixteen horizontal-bombing leaders of the First Air Fleet set out for intensive training under Furukawa’s direction. Genda hoped that at Kagoshima they would work up an intense competitive spirit and that intergroup rivalry would improve their marksmanship.36
Yamamoto knew even better than Genda that if Japan went to war, esprit de corps would be a strength no less sturdy for being intangible. He also wanted his personnel thoroughly indoctrinated in their jobs and able to work together with the ease of long practice. To this end, in the latter part of July he dispatched Kuroshima to Tokyo in an effort to prevent the kind of impending personnel shuffle that periodically upset the Combined Fleet.37
To a certain extent Yamamoto had brought this particular problem on himself. The two-year tour of duty had been instituted in the fall of 1939 at his own urgent request. This meant that about the beginning of August 1941 the Combined Fleet would experience the start of a mass turnover, to end some time in September. Because at least one month would be required to shake down the new personnel and during that month war preparations had to move along apace, the fleet might not be ready before the beginning of hostilities, “tentatively set for the end of October.”38
In Tokyo Kuroshima presented to Rear Admiral Giichi Nakahara, chief of the Navy Ministry’s Personnel Bureau, Yamamoto’s request that no more major personnel shifts be made. With all the conviction and fervor with which he always served Yamamoto, Kuroshima stated that widespread changes in the lower ranks would disrupt the intensive training and operational studies under way and would certainly impair efficiency by breaking up well-knit battle crews. But Nakahara pooh-poohed Kuroshima’s fears. “You should not expect war to break out in the near future,” he said. Surprised and angered, Kuroshima replied with asperity, “We who are responsible for the maritime security of Japan cannot take refuge in your explanation!”39
Kuroshima was convinced that Nakahara was a typical desk obstructionist. Whatever Nakahara felt beneath his official exterior, he refused to lose his temper or become involved in fruitless argument. He had to think in terms of long-range efficiency arising from diversified experience and training. The fleet must be flexible enough to absorb combat casualties and proceed with unimpaired effectiveness. He also had to ensure that the commanders did not become so accustomed to one set of officers that they came to use their staffs as crutches. So he would go right ahead with his transfers, knowing that within a few months all concerned would have settled into place again.
Therefore, Nakahara spoke to Kuroshima soothingly. “If the worst comes to the worst, you will have plenty of time to train new crews,” he pointed out. But he agreed that he would try not to move the lower ranks—junior officers, petty officers, and enlisted men—any more than absolutely necessary. “Please prepare a list of personnel who should not be transferred,” he directed. Though far from satisfied, Kuroshima agreed to do so and hastened back to Nagato.
Yamamoto punctuated Kuroshima’s report with grunts of disapproval, displeased that the Navy Ministry had not immediately honored his request. But he accepted the decision as philosophically as he could and ordered all units to compile the necessary lists.40 Nakahara was as good as his word. His Personnel Bureau cooperated in making the minimum changes among the First Air Fleet’s aircraft crews and those of the Sixth Fleet’s submarines, which it now appeared might also participate in the Pearl Harbor project.41