Pearl Harbor's Overlooked Answer

By Jonathan Parshall and J. Michael Wenger

The most important facet of the Japanese attack—the thing that made it so stunning—was the sheer number of aircraft involved. The Japanese did not just assault Pearl Harbor; they simultaneously hit every major airfield across the breadth of Oahu—Ewa Mooring Mast Field, Naval Air Station Pearl Harbor, Naval Air Station Kaneohe Bay, Wheeler Field, Hickam Field, and others—to remove American airpower as a threat to Kido Butai ’s carriers. Simultaneously hitting so many targets required massive numbers of planes—183 and 171 in the two attack waves. That was unprecedented.

In fact, Kido Butai was a truly revolutionary weapon system for its time because it embodied the conceptual leap from single-carrier to coordinated multicarrier operations. Kido Butai ’s ascendancy would last only about six months before it was permanently mauled at the Battle of Midway, but during that time there was nothing else like it. The U.S. Navy would not acquire a similar sophistication until roughly late 1943—more than two years later. 1

How had the Japanese developed such a revolutionary force without being detected? The answer lies in both inspiration on the part of the Japanese, as well as the enormous pressures imposed by the Imperial Japanese Navy’s frantic training for Pearl Harbor.

The mental seeds for Kido Butai were planted in 1940, when noted carrier pilot Lieutenant Commander Minoru Genda saw a newsreel of a group of American aircraft carriers parading for the camera in a box formation. 2 He began wondering what might be accomplished if large groups of carriers were used for doing more than showing off for theater-goers. Genda began pestering some of his like-minded superiors about the notion of creating a carrier fleet. The most important of these men, Rear Admiral Takijiro Onishi and Vice Admiral Jisaburo Ozawa, in turn began badgering Admiral Isoroku Yamamoto, commander-in-chief of the Combined Fleet. 3

Yamamoto, who was already contemplating attacking Pearl Harbor as part of a larger war plan, essentially decided to co-opt Genda’s notion and make it his own. As C-in-C, he had both the bureaucratic moxie and authority to do as he pleased as far as force structure was concerned. Therefore, on 1 April 1941, First Air Fleet was created. 4 For the first time in history, there existed a carrier force comprising enough aircraft to do strategically meaningful things on the battlefield. Instead of just scouting, Kido Butai had the ability to attack enemy fleets—and enemy fleet bases.

Authorizing the creation of a unified carrier task force was one thing; making it actually function was quite another. Japan’s carriers had sometimes operated in pairs and trios but never as a foursome (soon to be sixsome). Furthermore, they had never really coordinated their aircraft. During the summer of 1941, with war clouds looming, the Japanese set out to figure out how to do just that.

Commander Genda, not surprisingly, was given the challenging assignment of air officer of First Air Fleet. 5 It was now his job to bring his original vision to reality. Overall command of the force was given to Vice Admiral Chuichi Nagumo. The choice was uninspired because Nagumo was not an airpower enthusiast by any stretch. However, by rules of seniority Nagumo was next in line for such a fleet command. As a result, Genda had to develop Kido Butai ’s doctrine mostly by himself. To do so, he had to overcome the resistance of the carrier captains, who were not only senior to him but also loath to give up direct control over their own air groups. Genda knew there would be interesting times ahead.

The four heavy carriers available—the Akagi and Kaga and sisters Soryu and Hiryu —were formed into Carrier Divisions 1 and 2. Carrier Division 5, composed of the new sister ships Shokaku and Zuikaku , would be added later in the fall. There were myriad details to be worked out. Some were technical. In what formations should the carrier force steam together, and what ordnance should be carried? Other questions were more organizational in nature. How many aircraft, and of what types, should be launched by each carrier to create a combined strike force? How many escort fighters should be sent along as a covering force? How should the aircraft be organized during transit and attack? How should a unified strike force be commanded in the air? 6

As the summer of 1941 wore into the fall, those questions became more urgent. War was coming. Yamamoto knew that if his vision of attacking Pearl Harbor was to become a reality, Kido Butai ’s fighting edge had to be honed as rapidly as possible. What Genda needed was an inspiring attack leader who could command his force in the air. Commander Mitsuo Fuchida was given the job, taking over as air group commander on the flagship Akagi on 25 August 1941. 7

Fuchida was an excellent choice. Highly experienced, intelligent, and charismatic, he had the right combination of skills to lead a sophisticated battle force into action. Between Genda and Fuchida and their talented squadron commanders, the details were hammered out and a proficient force assembled. By 7 December Kido Butai could launch a combined air group from six flight decks, form up the aircraft, and send them on their way in 15 minutes. They could attack in coordinated groups and then re-form and return to their carriers en masse.

During this time, Japanese operational doctrine evolved quickly. Many of the patterns that naval historians view as “classic” features of early war Japanese carrier operations clearly had, in fact, only been practiced for a few months at most before Pearl Harbor. For instance, a Japanese carrier’s contribution to a combined air group typically constituted what was known as a “deckload strike.” 8 This package generally consisted of either the carrier’s dive-bomber squadron or its torpedo/level–bomber squadron, along with a section or division of escort fighters. The 21 to 36 aircraft fit conveniently on the flight deck and could be launched without interruption, or having to respot the deck.

Once airborne, each of Kido Butai ’s aircraft types—fighters, dive bombers, and torpedo/level bombers—regardless which carrier they came from, would be commanded by a single officer. However, this organizational structure—wherein the notion of a single carrier’s aircraft almost ceased to exist once they became airborne and incorporated into the larger strike package—had to be practically rammed down the throats of Kido Butai ’s carrier skippers around October 1941, just two months before Pearl Harbor. 9

The final piece of the puzzle was how to get Kido Butai to the objective. Hawaii was so far from the Japanese navy’s home bases that the smaller Soryu and Hiryu did not have the range to reach Oahu and still make it home. Indeed, one earlier iteration of the battle plan had them being scuttled off Hawaii once the mission was completed. 10 However, the Japanese began experimenting with various methods of underway refueling and quickly developed a rudimentary competence in the procedure. It was an ability the U.S. Navy did not know about. This isn’t surprising, because it is clear from surviving Japanese records that the Hawaiian mission was practically the first time the capability had ever been used in practice. 11 Combined with the expedient of stuffing every spare space on board ship with extra fuel barrels, the Japanese improvements were sufficient to get Kido Butai to within attack range of Hawaii and back. 12

The picture that emerges is of an enemy carrier force whose capabilities in late 1941 were mutating almost overnight. The Kido Butai of December 1941 was entirely different from the force that began exercising together in the summer of that year. It was 50 percent larger in terms of flight decks, could make much longer voyages, and was capable of speedily launching and efficiently coordinating huge groups of attack aircraft. In their frantic efforts to prepare for Pearl Harbor, the Japanese had created a brand-new monster.

Consider the difficulties of tracking the development of this particular beast. You are an American naval intelligence officer and probably relatively junior in rank. You may or may not have any naval aviation experience. Via traffic analysis, naval attaché reports, and other sources of information, it is your job to keep track of Japan’s carrier force and predict what it’s up to. But in the final analysis, you are the product of a navy that has not made the same conceptual leap that your enemy has. As far as you know, carriers are used for scouting purposes in conjunction with the battle line. They operate solo.

The only wartime attack by a carrier against a fleet anchorage—the Royal Navy’s raid against Taranto, Italy, in November 1940—had been made by a single flattop (HMS Illustrious ), operating at night to avoid detection (and destruction). The Illustrious launched a grand total of 21 aircraft against the enemy. You don’t know anything about multicarrier operations because your navy has never conducted such operations. Not only that, but as far as you know, underway replenishment is something the U.S. Navy is good at, but pretty much no one else is—meaning Hawaii is likely out of range of Japan’s carriers in any case.

How would such an individual, the product of such a navy, be expected to understand the advances the Japanese had made when none of his superiors had made similar leaps? How could such men be expected to accurately predict the capabilities of such an enemy?

The answer is that they couldn’t. This is made clear by the statements of contemporary U.S. Navy officers. During Admiral Thomas C. Hart’s 1944 inquiry into the 7 December attack, Rear Admiral Arthur Davis—former Pearl Harbor naval commander Admiral Husband Kimmel’s staff air officer—remarked that he had not realized “to what a high degree of proficiency Japanese naval aviation had been developed. I do not believe that anybody else in the American Navy had any proper conception of this development, either.” 13 It was Admiral Davis’ job to know about such things. That he apparently did not, and that U.S. Naval Intelligence did not, is a truly striking failure.

This lack of comprehension was largely due to two factors. First was Japan’s near-total effectiveness in preventing Western intelligence agencies from learning any hard details about their naval building programs. One scholar of American naval intelligence recently remarked that quality information on Japanese capabilities “existed hardly at all for much of the interwar period.” 14 The U.S. Navy had no real knowledge of such prominent weapon systems as the Yamato -class superbattleships, the A6M “Zero” fighter, or the advanced Type 93 “Long Lance” torpedo. It is hardly surprising that hard data on Kido Butai ’s size and composition were lacking as well.

But beyond a simple lack of information about Kido Butai ’s physical assets lay an ignorance of Japanese doctrinal advances that underlay the employment of its carriers. By its very nature, doctrine is intangible. You can’t see it, hear it, touch it. Typically, you can only understand an enemy’s thinking by observing his training exercises, reading his professional literature, or acquiring his actual doctrinal tracts. But Kido Butai had hardly any published doctrine; it was being made up as the training for Pearl Harbor proceeded. Moreover, the U.S. Navy was professionally disinterested in enemy doctrine. According to historian Douglas Ford: “U.S. commanders tended not to monitor foreign doctrines and weapons development in a methodical manner. Naval intelligence was subsequently not tasked to investigate ongoing innovations unless the Americans were simultaneously pursuing them.” 15

As a result, most U.S. Navy assessments of Japan’s naval aviation force painted a picture of mediocrity and weakness. Not only that, but the Navy also assumed that the Japanese held these same perceptions and would therefore employ their carrier force defensively. 16 All of these American preconceptions were wrong, and only war would set them right.

Analogies between Pearl Harbor and the 9/11 World Trade Center attacks are very instructive with respect to enemy innovations. By the early afternoon of 11 September 2001, it was obvious to an untold number of people that multiple commandeered civilian airliners, piloted by fanatics and properly coordinated, could inflict devastating structural damage on skyscrapers, leading to massive civilian fatalities. However, on 10 September 2001, the number of people worldwide who could have envisioned all the facets of such an attack probably numbered only a few dozen, and most of them were working for al Qaeda. Hijackings were not new. Bombing the World Trade Center was not new. But assembling all the disparate pieces to make a larger, more coordinated, vastly more destructive and suicidal attack was new.

The same was true of Pearl Harbor. After Taranto, carrier raids with a single carrier were not new. Nor was using a carrier to sink a battleship at anchor. What was new was assembling a huge carrier force, transiting thousands of miles to the objective, and then using hundreds of aircraft in broad daylight to simultaneously crush multiple airfields and a major fleet base. Outside of the Japanese navy, almost no one could comprehend such a massive, coordinated operation. That is what made the attack so psychologically devastating—the indisputable evidence of a substantial capability that no one had suspected existed.

Another analogy between Pearl Harbor and 9/11—the search for scapegoats and development of conspiracy theories—is also worth noting. It is human nature to search for causes beyond the norm to explain the underlying contexts of harrowing, humiliating defeats. This need is seemingly universal and has led to the creation of endless parallel realities down through the years, for example the Confederacy’s “Lost Cause” and Germany’s World War I “Stab in the Back.” It is no wonder that Pearl Harbor and the 9/11 attacks have each spawned a rash of such misbegotten notions—after all, both attacks still have an element of the fantastic about them.

But such searches for externalities serve to mask a universal and unpleasant truth: Even large, sophisticated, professional militaries almost inevitably are handed unforeseen defeats. Some are big, some small, but they happen. No matter how good you are, your opponent occasionally goes one level deeper in his analysis or has a capability you never anticipated. That is the unvarying nature of war. When the enemy does that, nasty surprises are the inevitable result. And the surprises are particularly nasty when the other side has made a major conceptual leap you have yet to make yourself. Such was the nature of Germany’s blitzkrieg . And such was the nature of Kido Butai ’s debut on the world naval stage.

In the end, Kido Butai ’s extraordinary capabilities availed Japan nothing. Indeed, the Japanese themselves did not seem to understand clearly the nature of the weapon they had created, or how best to wield it. Within six months of the opening of the war, poor strategy on the Imperial Japanese Navy’s part would end up committing Kido Butai ’s component carrier divisions piecemeal, first at the Battle of Coral Sea and then at the Battle of Midway. During the latter, Kido Butai was decisively defeated—with four of its carriers sunk. Japan’s overwhelming early war numerical advantage was thus erased. Shortly thereafter, America’s superiority in production began asserting itself.

It would be left to the Americans to take the concept of a large carrier raiding force to its apotheosis by backing it up with underway logistics and forward-deployed repair facilities. The stunningly powerful carrier task forces that the U.S. Navy wielded in 1944–45 were as much superior to Kido Butai as the latter had been to the Illustrious ’s solo attack against Taranto. Thus the shock of Japan’s unsuspected carrier aviation capabilities in 1941 helped lay the foundation for an even more lethal weapon system.


1. Operation Hailstone—the U.S. Navy’s attack on Japan’s naval anchorage at Truk, and its first usage of massed carrier strike, did not occur until February 1944.

2. Mark Peattie, Sunburst: The Rise of Japanese Naval Air Power, 1909–1941 (Annapolis, MD: Naval Institute Press, 2001), pp. 248–49.

3. Gordon W. Prange, At Dawn We Slept: The Untold Story of Pearl Harbor (New York: McGraw-Hill, 1981), pp. 102–103.

4. Peattie, Sunburst , p. 151.

5. Prange, At Dawn We Slept , p. 110.

6. These matters are addressed in more detail in a forthcoming work on Pearl Harbor coauthored by Michael Wenger, Robert J. Cressman, and John F. Divirgilio, and drawing from Wenger’s research into Japanese documents regarding the training before the battle.

7. Prange, At Dawn We Slept , p. 195.

8. Jonathan Parshall and Anthony Tully, Shattered Sword: The Untold Story of the Battle of Midway , (Dulles, VA: Potomac Books, 2005), pp 86–87.

9. Wenger’s research, drawn from the papers of Gordon W. Prange.

10. Prange, At Dawn We Slept , p. 280.

11. Donald Goldstein and Katherine Dillon, The Pearl Harbor Papers: Inside the Japanese Plans (Dulles, VA: Brassey’s, 1993). See Chapter 13, “Conquer the Pacific Ocean Aboard the Destroyer Akigumo : War Diary of the Hawaiian Battle,” pp. 169–220.

12. Prange, At Dawn We Slept , pp. 322–23.

13. Hearings Before the Joint Committee on the Investigation of the Pearl Harbor Attack (Washington, DC: Government Printing Office, 1946), Part 26, Proceedings of the Hart Inquiry, Testimony of RADM Arthur C. Davis, 13 March 1944, p. 105.

14. Douglas Ford, manuscript copy of The Elusive Enemy: U.S. Naval Intelligence and the Imperial Fleet (Annapolis, MD: Naval Institute Press, 2011), p. 20.

15. Ibid., p. 29.

16. Ibid., p. 47.


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