by Attack on Pearl Harbor: Strategy, Combat, Myths, Deceptions
There were transfers from the light carrier air groups to fill out the fleet carrier complements, particularly to obtain sufficient A6M Zero pilots, but a wholesale transfer of B5N Kate or D3A Val complements from one carrier to another had never been previously done, and would likely have generated an instinctive rejection from most senior aviators.
If the B5N Kate aircrews were all concentrated on a few carriers for the attack and then lost at Pearl Harbor, all the surviving carriers would have to carry on the war with an unbalanced air complement. Without B5N Kates, the remaining carriers would not have a killing capability against battleships.
An attack on Pearl Harbor with just the D3A Vals would have lacked killing power against battleships, but could have destroyed carriers and cruisers. This was acceptable to Genda, who considered the carriers the main objective, but would not satisfy Yamamoto.
It is not surprising that both concepts were rejected.
Deck Capacity
With 30 knots of wind across the deck, about 250 feet of deck run was required to launch a fighter, more for the heavily-laden bombers. With carrier flight decks 750 to 850 feet long, 500 to 600 feet were available to stage the aircraft to be launched in one “go.”3
The first deckload of aircraft would launch and immediately form up and depart to the target. The aircraft remaining in the hangars would be lifted to the flight deck and positioned aft, and then have their engines started for warm-up, a process lengthy enough to eliminate thoughts of having the first group loiter awaiting the second launch so the attack could proceed in a single wave.4 Spotting the deck took approximately 40 minutes, limited by the cycle times of the elevators, with Kaga’s the slowest. Engine warm-up took 20 minutes. With these restrictions, the second wave was expected to launch about one hour after the first.5
Doctrine
In 1941 Japanese doctrine had carriers operating in two-ship divisions. Search missions and local patrols would be carried out by battleship and cruiser float planes as much as possible, augmented by carrier aircraft when necessary, reserving the carrier aircraft for offensive missions. The practice was to spot on deck some fighters for CAP and strike escort duties, along with the entire ship’s complement of one type of bomber. One carrier would launch its entire complement of D3A Vals and the other its complement of B5N Kates, whereupon they would join into a single combined-arms strike. This allowed unit integrity, with each bomber type under its own commander from its own ship operating with the men they knew and with whom they had trained. Their attacks would have a greater cohesion than if each carrier launched mixed groups of bombers.
This was good doctrine. Throughout the war the Japanese were able to launch and form up strikes in a minimum of time, something with which the Americans had problems until later in the war.6 But it did constrain the Japanese from deploying their aircraft largely on a unit basis. In contrast, the American practice was more “mix and match,” launching deckloads of mixed bomber types and mixed squadrons to meet the requirements of the specific mission and immediate availability of aircraft.
Vulnerable Torpedo Bombers
The torpedo bombers had to lead the attack. These aircraft were restricted to an unusually “low and slow” attack profile to accommodate the narrow launch envelope required by the modified shallow-water torpedoes, making them easy targets for AA gunners. The torpedo bombers had to slip in their attack before the AA gunners were awake, oriented, armed, and firing.
Aircrew Training and Experience
The air groups on Zuikaku and Shokaku were only recently formed and many of the aircrews were young and inexpert. In the words of one Japanese pilot, they were “really green” with “very little flight experience.”7 It would be most reasonable to assign them the easier and less critical missions requiring less skill and precision—which meant OCA, airfields and aircraft.
Fighter Employment
The Japanese fighters were considered offensive weapons, not defensive, in the sense that they were expected to range out and attack the enemy, not sit back in a defensive role as escorts or CAP. Their thinking was that “offense was the best defense” when it came to ensuring that their bombers made it through.
As previously mentioned, SEAD against ground targets was a neglected capability and not really in their repertoire or their mindset in 1941. However, the fleet practiced SEAD in attacking warships at sea. An “out of the box” thinker might see the need to apply this cooperation in the Pearl Harbor attack.
Genda, the lead planner, was a fighter pilot. For all his reputed brilliance, his thinking was firmly within the usual Japanese fighter pilot paradigm, locked in the box.
“Stovepipe Thinking”
Japanese doctrine characteristically lacked a combined arms approach, a deficiency called (in modern terminology) stovepipe thinking. There was little inclination to solve problems in a mutually cooperative manner. Dive bombers, torpedo bombers, and fighters all had their separate missions. The concept of having one type assist another type perform a mission was not in their worldview. They certainly considered the best order for the aircraft types to deliver their attacks, but this was to facilitate the individual attacks and reduce mutual interference, more than out of any motives of cooperation or mutual support.
The Japanese would recognize the need to break out of their stovepipe thinking later in the war, but would never really succeed.
Air-to-Air Communications
Important planning considerations rested on the ability of aircraft to communicate. Inter-aircraft communication capabilities define how much control a commander has over his forces aloft, his ability to adjust to circumstances, the flexibility to take advantage of unforeseen errors by the enemy, or even just to allow switching from one plan to another. Good communications allow better coordination of forces and dissemination of sighting reports and on-scene intelligence. Most significantly to the Pearl Harbor attack force, it would allow control of the force by a commander with better overall situation awareness, in particular, the ability to control fighters and the ability to control the distribution of the bombers to gain the best effect from each bomb and torpedo.
This is a significant capability. The attack would be the first combat action for nearly all the Japanese aviators, as most of the aviators on the newly commissioned carriers were young, mostly under 20, and would need supervision by more experienced hands, but also because the second wave would need information on the damage caused by the first wave to optimize their targeting.
It wasn’t until 1940 that the Japanese Navy first established its own capability to produce and install radio sets for aircraft, and 1941 when plans were established to retrofit radio sets into existing aircraft on a large scale. Even then, their production goals were woeful—for 1942 they planned to produce four types of long-range aircraft HF radios for a total of 1,000 sets per month, and only 100 short-range aircraft radiotelephones per month, at a newly established plant at the Numazu Ordnance Depot.
The standard was to have each multi-seat carrier aircraft carry an HF set and a radiotelephone, and each fighter carry a radiotelephone, by December 1941. All the aircraft of the Kido Butai may not yet have been fitted in time for the attack.8
The standard of installation was poor. The radios were practically unusable. The bulky sets were jammed into aircraft not designed to accommodate them, and little consideration was given to ensure the sets could be worked. Controls often could not be manipulated to exact settings. The sets did not fare well in a high-vibration environment that varied from steamy hot to sub-zero. Controls might be awkward to reach and dial scales out of sight. Vibration caused knobs to drift off their settings. Operating the sets at high altitude was nearly impossible. The aviators complained that some installers were more interested in getting credit for the installation than in leaving a working radio. Testing was perfunctory and haphazard. Careless supervision and poor installation resulted in wiring problems and electrical grounds. The discharges of engine spark plugs would interfere
with reception.
Lieutenant Commander Arima Keiichi, a dive bomber observer assisting the research department in 1944 to develop communications equipment, testified:
I feel strongly that Japan was inferior to the United States regarding wireless communication. During the war Japan mainly used Morse code, but American aviators were able to use voice modulation gear. We were not able to use voice modulation gear well, but regarding Morse code we were superior.9
The air crews, particularly fighter pilots, became indifferent to the use of their radiotelephones.10 Radios interfered with fighter pilots’ concept of themselves as independent samurai warriors. Lieutenant (junior grade) Harada Kaname, a Soryu A6M Zero pilot, related that at the time of Pearl Harbor:
We had a radio communication system, but it was primitive, so we didn’t use it much. Japan had limited technology, and we were told to use the Morse signal. If the enemy came the signal was like to-to-to, but this signaling was difficult to do sometimes, so we often used hand or facial signals. You could do these types of signals within a small group, but if we tried to communicate with another small group it was very difficult. Hence, each small group made decisions with the guidance of their leader, in accordance with the situation.11
Radio communications problems were not unique to the Japanese Navy. CDR Scott Smith, speaking of the first six months of the war, attested that “radio communications in those days was just short of miserable.”12 In particular, intermittent communications between the escort fighters and the bombers at the Battle of Midway was a contributing factor in the horrendous losses suffered by the torpedo bombers.
These problems continued and were evident particularly at the Eastern Solomons and Santa Cruz battles. American aircraft radios tended to drift off the precise frequency required by the sensitive voice transmitter. After the Battle of Santa Cruz, one angry flight commander who had lost communications with two-thirds of his aircraft, wrote:
The present radio equipment cannot be set exactly on frequency in war waters, and unless it is, all future attacks will be doomed to similar failure. The set is too complicated for aircraft operation. The rear-seat gunner has plenty on his hands without fiddling with all of the radio dials in flight… If radio equipment is so complicated that it cannot be operated by personnel in flight, it should be thrown out and changed immediately.13
American radios were superior to Japanese equipment. Judging from the Americans’ problems, one can imagine the challenges Japanese aviators faced.
The Japanese mostly ignored their nearly inoperable voice radio equipment. Anecdotally, it appears that little (if any) use of the radiotelephone was included in Japanese plans for Pearl Harbor, or used in practice. Communications appeared restricted to limited HF continuous wave radio, Morse signals, and visual signals. The famous attack order, Tora Tora Tora, was sent over keyed HF. Flares were used to communicate “surprise” or “no surprise.” When the flares were misinterpreted, veterans did not mention any attempts via radiotelephone to correct the error and bring the formations back under control.14
A poignant incident during the attack shows the norm for Japanese aerial communications. A fighter was leaking fuel and the pilot knew he had no chance to return to his carrier. To his wingman, he pointed to his mouth (the sign for fuel), gestured that his fuel was low, smiled, waved, and rolled his plane into a final suicide dive. There was no attempt to use the radiotelephone, even for last words.
Certainly radiotelephones were in ill repute among Japanese naval aviators at least through 1943, and it is unlikely that they would rely on the equipment for anything tactically critical. There are stories during the Solomons campaign of Japanese fighter pilots personally tearing out their radio equipment in order to lighten their aircraft and gain a bit more speed and maneuverability.15
Radiotelephone limitations restricted Japanese planning. Communications deficiencies restricted how ship-killing ordnance could be coordinated. In particular, it forced more responsibility on the leaders of shotai and chutai in selecting targets and directing the attack. There simply were no reliable communications with higher leaders.
Target Selection and Weapons Delivery
With limited inter-aircraft communications, much responsibility was placed on the shoulders of the aircraft commanders when it came to target selection. The Japanese bombers operated in shotai of three aircraft. The shotai leader—or, in larger attacks, the chutai leader of three shotai—would select the target, and the other aircraft would simply follow. However, individual aircraft commanders had the authority to select a different target.
For the D3A Vals, the shotai was an important unit, as their divebombing technique had the following aircraft adjusting their aim point based on the fall of the leader’s bomb. If the shotai became separated, significantly reduced dive-bombing accuracy could be expected.
Limitations and Constraints—Summary
The planners had significant constraints, some imposed by their equipments, some from their doctrine, and some from the limitations of their own thinking. Recognizing self-limitations was not an area in which the Japanese excelled—a culture where errors could result in suicide tended to limit thinking outside of societal norms.
This analysis will proceed to compare the Japanese planning and attack against what was theoretically possible, while noting the source of the shortfall, whether from doctrinal constraints, mental errors, or errors in execution. An alternative approach, determining a perfect attack within the constraints of Japanese doctrine and thinking, would be very problematic, since characteristically there might be many reasons behind a shortfall, and it might be impossible to determine them all. As will be seen, most of the Japanese shortfalls had solutions that could have been achieved within the technology of the period, if only the problem had been recognized and some thought given to its solution. In most cases the planners were restricted in their ideas of what was possible, and accepted their limitations as a matter of course.
Within the above constraints, the planners had the flexibility to determine the aircraft types to employ in each wave, what targets to hit and in what order, what weapons to use on each aircraft type against each class of target, and how fighters were to be allocated and employed. These issues were significant challenges alone.
Planning for Pre-strike Reconnaissance
The Japanese plan included submarine and aerial reconnaissance immediately prior to the attack.
A submarine would scout the Lahaina Roads anchorage off Maui a day prior to the attack and transmit a report. This would be a fairly lowrisk mission, and the information would be critical. If the fleet was located off Maui at anchor, the attack would have to be redirected and the armament mix changed. The level bombers would not be needed, and those fifty aircraft re-armed with the more lethal torpedoes. If only part of the fleet was out, the attack would have to be split and armed accordingly.
Two cruiser float planes would be launched in the pre-dawn hours before the attack. One was to scout Lahaina Roads again, presumably to check if the fleet had departed the anchorage since the submarine’s report, while the other went to Pearl Harbor for reconnaissance and to transmit a weather report.
Shortly after 0600, with hardly any light to mark a horizon for the pilots, the carriers were to launch the first wave of the attack. At 0630 the battleships and heavy cruisers would launch 16 float planes to scout to the east, south, and west. Japanese reconnaissance doctrine differed from that of the Americans, in that float planes were more used for long-range reconnaissance, while the Americans used carrier aircraft. The Japanese doctrine was good, in that it preserved the carriers’ aircraft for offensive operations, maintained unit integrity, and kept carrier decks from being tied up to recover the reconnaissance aircraft. Its weakness was that the float planes from the battleships and heavy cruisers were stored exposed to the weather, and were not as reliable. In addition, the float plane aviators got fewer hours and were not the same quality as carrier aviators.
&nbs
p; Later, at Midway, the American system showed its warts when the three American carriers could not put together a coordinated strike, as one carrier had to delay her launch while recovering reconnaissance aircraft. But the Japanese system made the critical error. A reconnaissance float plane was delayed in launching, making it fatally late in discovering the American carriers.
The second wave would be launched at approximately 0730, one hour after the departure of the first wave.
Fuchida’s Claim Regarding Level Bombers
Fuchida was first introduced to the Pearl Harbor attack plan in a meeting with Genda in late September 1941, immediately after Fuchida was transferred to serve as the strike leader aboard Akagi.
According to Fuchida, the plan Genda showed him did not include level bombers with AP bombs. “The Japanese Navy had a terrible record of hits using this technique,”16 scoring less than 10% hits in exercises the previous June. In addition, AP bombs had a tiny charge of explosives compared to torpedoes. Aviators in the IJN had argued for some time that level bombing was an inefficient use of resources and would not score enough hits to justify its use. At one point the First Carrier Division recommended that horizontal bombing should be abolished.17
Fuchida, a level bombing specialist, claimed he pressed Genda to add level bombers. AP bombs, Fuchida asserted, would be needed against ships inaccessible to torpedoes. He pointed out to Genda two things: torpedo nets could protect all the ships from torpedoes, while double-berthing ships side-by-side would shield the inner battleships.18 Fuchida claimed his arguments convinced Genda, and as a result level bombers were included in the attack plan.
This conversation likely did not occur.
First, Fuchida spoke as if Genda was not aware of the implications of double-berthing battleships or of torpedo nets. Considering Genda’s reputation for brilliance, such gaps in his knowledge are highly unlikely.
