Author: Attack on Pearl Harbor: Strategy, Combat, Myths, D
Category: Thriller
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No fighters (or bombers) were allocated for SEAD. It was as if the concept did not exist, or that the fighters had their own missions and would not be bothered to help the bombers along the way. “Combined arms” and “mutual support” were concepts absent from the Japanese lexicon.
The planners spread the available fighters nearly evenly over all the formations, regardless of the numbers or importance of those planes in the mission plan. The military proverb, “He who protects everything, protects nothing,” applies. If the American forces at Hawaii had been in their usual readiness and detected the approach of the strike, and if the US fighters had massed over Pearl Harbor to protect the fleet (as was their responsibility), it is likely that the torpedo bombers’ attack would have been thwarted.
One capability of their new fighter that the Japanese did not exploit was its incredible endurance. In the months before the beginning of the war the Japanese developed techniques to stretch the range of the A6M Zero to unheard-of lengths. Cruising at 115 knots at 12,000 feet, an A6M Zero with an average pilot at the controls could consume as little as 18 gallons per hour out of a normal fuel load of 182 gallons, giving ten hours in the air.37 First-wave fighters launched at 0600 could have remained over Oahu for hours after the second wave had departed, if asked to do so. First-wave fighters could have been posted over each of the airfields and remained for the duration of the attack, ensuring that nothing got off the ground until after the second wave had come and gone. On US carriers this was known as “double cycling,” and was usually done only with scout bombers on inner and outer AS patrols. US Fighters could be double-cycled after drop tanks were developed.
Evidently no thought was given to taking advantage of the A6M Zero’s endurance. Instead, the fighters went in to the attack, expended their ammunition immediately, and joined up at the strike rendezvous point so the bombers could navigate them back to the carriers. The plan allowed the Americans a hiatus in the attack, time to recuperate from the effects of the first wave, recover and rearm what fighters they had gotten aloft, and prepare for the next wave.
Bomber Allocation for the Main Effort
The Intelligence Foundation
The Japanese were blessed with extraordinarily good intelligence for their attack. The Japanese Navy assigned a reserve naval officer, Yoshikawa Takeo, a graduate of the Japanese naval academy who had been medically disqualified from active duty, as a member of the Japanese legation on Oahu. While posing as a diplomat, his true role was kept secret from the legation staff. His neglecting of his “duties” at the legation scandalized the regular diplomatic staff, as he traveled about Oahu under the guise of a gadabout.
Almost daily he traveled to a tourist overlook surveying the beauties of Pearl Harbor and counted the fleet, noting mooring locations. He recorded the fleet’s operating patterns. He determined the day of the week when most ships would be in port. He took tourist flights over the harbor, one on the 5th of December accompanied by two young ladies of questionable repute, a rather ingenious and amiable way to conceal intelligence activities. He attended open house events staged at the various bases, where he was allowed to wander about unsupervised. He worked in the kitchen at the Pearl Harbor Officer’s Club, with access to the base and the officers’ gossip. Attending a “Galaday” at Wheeler Field in August when the airdrome was dedicated, he inspected the facilities thoroughly.
Planners from the Naval General Staff also traveled to Hawaii aboard the civilian liner Taiyo Maru. This ship traveled along Kido Butai’s intended route to take weather observations, gauge the density of traffic (no ships sighted), and observe American reconnaissance (ineffective). At Honolulu they delivered an extensive list of questions to Yoshikawa regarding Pearl Harbor and its defenses.
Yoshikawa divided Pearl Harbor into numbered squares and transmitted the locations of ships. Periodic messages to the Naval General Staff in Tokyo, sent through diplomatic channels, included the specific anchorages and moorings occupied by the ships, along with listings of daily arrivals and departures. Kido Butai received one of these messages the day before that attack, with the information a day late due to being retransmitted from Tokyo. As Kido Butai approached Hawaii, Yoshikawa provided last minute tactical intelligence on anti-submarine nets at the entrance to the harbor (yes), anti-torpedo nets around the battleships (no), and barrage balloons (no).
The aviators had nearly exact information on the locations of moorings and berths and, more importantly, which normally hosted battleships and carriers. Each pilot was provided a map with the locations of their targets and the location of ground AA positions. They also were given aerial “Souvenir of Honolulu” photographs of the naval base. Copies would be found in aircraft shot down during the battle.38
The Japanese had a firm intelligence foundation upon which to plan and execute the attack.39
Operational Approach
Some of the most important decisions involved the overall concept of how the operation was to be executed, including the manner in which targets would be allocated to specific attackers, the attack order and timing, ingress and egress routes, and coordination.
Targets could be allocated in several ways. Under one option, specific aircraft could have been directed to hit specific targets. Alternately, a prioritization scheme could be used where the pilots were given general instructions regarding the types of targets to hit and in what order, with the aviators selecting their specific targets upon arrival. A compromise between the two would be for attackers to select specific targets out of an assigned area.
Each method has advantages and disadvantages.
Assigning aircraft to specific targets would give a better distribution of weapons over the intended targets, and would not require the aviators to make difficult target selection decisions when stress would be high. However, weapons could be wasted and confusion could result if the intelligence was inaccurate or if ships had moved since the last update. Pilots would still be required to recognize appropriate targets and avoid wasting weapons on inappropriate targets, something more difficult to achieve under combat conditions than might be suspected. Alternate targets could be pre-assigned, or the aviators could be given the freedom to independently find a target, or they could be directed to a marshalling area to serve as a reserve to be directed to a new target by the strike commander.
In contrast, a prioritization scheme would be most flexible to changes and conditions, but would require the aviators to make critical decisions under difficult conditions. Excellent visibility would be needed. And, somehow, the decisions of all the individual aircrews would need to be coordinated in the absence of radio communication to get the best performance out of the group as a whole, or else the possibility that all the aircraft would concentrate on a single high-priority target would have to be accepted.
Prioritization works best when targets are hit one at a time, so when the priority 1 target was destroyed the attackers could move on to the priority 2 target, and so on. But if the attack was to be simultaneous, or if individual pilots could not see the results of previous attacks, they would not have sufficient information for good decisions.
The Japanese combined features of both of these approaches. One group would go after carriers, one after battleships, and if anything unanticipated happened, the pilots were to find and attack anything suitable.
Prioritization
Three distinguished historians have recorded that the torpedo bombers used a prioritization scheme for assigning targets, as recorded in the Japanese official history of the war:
Japanese operational priorities were defined as battleships and aircraft carriers, in that order, and the Kates of the first attack formation were given the task of dealing with American battleships. Because of the efficiency of their intelligence sources, the Japanese basically knew where individual battleships would be found and had listed them in numerical order of priority from one to eight. The Kates were under instructions to attack the first four American battleships in order of
priority and there [after]; if carriers were in the anchorage, they were then to direct their attention against these. If carriers were absent, the Kates would be free to attack the battleships listed five to eight. The Vals, which were equipped with 250-kilogram bombs, were given the task of dealing with American carriers. If these were absent, or in the event of the first attack formation having accounted for them, the priority of the Vals was to be American cruisers, and only after the cruisers had been destroyed was priority to be afforded to the battle line.40
This account does not square with the operations orders, the testimony of the pilots, and the actual organization and execution of the attack.
According to the Combined Fleet Operation Order No. 1, the “Targets for attack are land-based air power, aircraft carriers, battleships, cruisers, other warships, merchant shipping, port facilities, land installations,” presumably in that order.41 According to the Carrier Striking Task Force Operations Order No. 3, “The targets of the first group will be limited to about four battleships and four aircraft carriers; the order of targets will be battleships and then aircraft carriers.”42
There was a gap between what the planners put on paper and what the warfighters were told to do. When interviewed postwar, many of the torpedo bomber aircrew specified that they were assigned to attack carriers as their first priority.
It appears that there were different official prioritization orders, apparently meant to placate different audiences. The Naval General Staff, anxious that Kido Butai be preserved, were told that enemy’s means to mount a counterattack was first on the strike list; Yamamoto was told his battleships would have top priority. The aviators actually executing the attacks had the final say, and consistent with their belief that battleships were not as important as carriers, they were focused on taking out the carriers first.
As in most organizations, there are the official instructions, the real instructions given to the troops, and the instructions they actually execute. The torpedo bombers, with Murata in overall command, were organized into two groups, one to attack carriers at the carrier anchorage west of Ford Island (16 Soryu and Hiryu bombers under Lieutenant Matsumura Hirata), and one to go against Battleship Row (Murata’s 24 bombers from Akagi and Kaga).
If targets were missing or destroyed by previous aircraft they were instructed to go find another target. The priority for alternative targets was carriers, battleships, and cruisers for the Soryu and Hiryu aviators, battleships for the Akagi and Kaga aircraft.
The prioritization scheme contained in the Japanese official history is overly complex and would be impossible to execute in combat, especially in the absence of excellent inter-aircraft communications, in an operation where pilots were scrambling to get in their attack before the AA defenses woke up. Aircraft were expected to attack “nearly simultaneously” in four long streams of bombers with planes at seven-second intervals. In the absence of reliable radio communications, in this formation leaders could exert only the most rudimentary “follow-me” leadership. Down on the deck, the rearmost planes in the string of attackers would not have the information to be able to make a reasonable decision regarding how far along the priority list the attack had progressed in order to properly allocate their own attack. To expect junior aviators to make such decisions while under fire for the first time, while flying 60 feet over the water in a wallowing torpedo bomber was unrealistic.
The official history prioritization scheme was more likely the story that was briefed to senior officers and the Naval Staff. The organization and actual execution of the attack indicate that Genda and Fuchida, on the cutting edge, considered things differently. Forty percent of the available torpedo bombers were to immediately attack the carrier moorings. This group would not wait to see if battleships one through four were hit. They were after carriers, pure and simple.
The choices available to the Japanese were constrained by their air-to-air communications. There are no reports that they used radiotelephones for tactical command and control. Their decision was to give guidance to the aircrews on target selection and the authority to choose their own targets. They then selected an attack formation for the torpedo bombers—a long string of aircraft one at a time separated by 500 meters—that eliminated any possibility of meaningful command by their formation leaders. Considering that most of the aircrews were young and inexperienced, these decisions effectively abrogated any possibility that the more mature leaders could influence the course of the torpedo attack.
Torpedo Bombers
Initial Calculations
Yamamoto himself wanted battleships sunk. One would expect that battleships would be allocated the bulk of the ordnance. There were also the carriers, a major risk to Kido Butai that had to be hit to prevent them from counterattacking. Any remaining torpedoes could be directed against cruisers. The Japanese operations order also listed auxiliaries and merchant shipping as potential torpedo targets, but they were at the bottom of the priority list, and there were no torpedoes to spare.
There are several ways the Japanese might have calculated their allocations. One of the most revealing methods is as follows. Assume that maximum firepower was wanted against the battleships. Allocate the minimum forces against the carriers, and send the rest against the battleships.
Two torpedo hits would cripple a carrier and prevent it from getting underway. Two carriers were operating out of Pearl Harbor; if they were both in port, four hits would be required. Assigning one additional attacker against each carrier to account for misses would result in six torpedo bombers allocated against the carriers, leaving 34 to go against battleships.
The Pacific Fleet had eight battleships. This would result in potentially as few as 4 torpedoes per battleship as a lower limit. If ships were double-berthed or in drydock there might be as few as four battleships accessible to torpedoes, giving an allocation of 8 torpedoes per battleship.
Battleship Row Attack Group
Akagi’s and Kaga’s 24 bombers would approach the battleship anchorages and engage from the east. If moored singly there could be six battleship targets accessible to torpedoes, but more likely four.
In addition, across from Battleship Row was the flagship Pennsylvania’s usual berth along 1010 Dock. Attackers would have to approach this target from the southwest. It was not occupied by a battleship on the day of the attack, but rather by an antique minelayer moored outboard of a modern 10,000-ton cruiser. Pennsylvania was in drydock.
The torpedo bombers would attack first. There were good reasons for this: the torpedo planes had a very narrow launch envelope. Pearl Harbor was too shallow for standard aerial torpedo approaches.
Torpedoes dropped from the B5N Kate in their normal delivery profile would generally dive down to at least 100 feet and sometimes as deep as 150–300 feet before rising to their running depth. This technical problem was overcome by modifying the torpedoes with wooden vanes on their tail to slow their entry into the water and provide an immediate nose-up pitch, and by modifying the delivery profile of the aircraft so that the torpedo bomber at weapons release would be “low and slow”—20 meters altitude, 140 to 150 knots, level attitude, gear and flaps up, as opposed to more usual drop parameters of 200 knots from 100 to 300 foot altitude.43 At 20 meters, the pilots had to estimate altitude by comparing the aircraft’s wing length to the distance above the water, a rather harrowing process that would keep the pilot’s head out of the cockpit (away from monitoring airspeed and attitude) and looking to the side of the aircraft (away from the target). Too high, and the torpedo would dive too steeply and hit the harbor bottom; too low, and the torpedo might broach or skip on the surface and break up.44
The slow speed and low altitude would make the torpedo bombers easy targets for AA fire or fighters. Thus, the torpedo attack had to be launched before the enemy was fully alert. The warhead was also modified to arm after only a short distance through the water, about 650 feet.
Three of the specially modified torpedoes were dropped for tests. Two
ran successfully; the third hit bottom at 39.3 feet. “On that basis the Japanese estimated that, out of 40 drops planned for Pearl Harbor, 27 would hit home.”45
The best of the practice runs occurred in early November, days before the end of training. The torpedo bombers achieved 82.5% hits. With this percentage, 19 hits could be expected from the 24 bombers allocated to attack the battleline. If the attack was distributed evenly over six battleships, that would give three hits per battleship, which according to Japanese thinking was sufficient to cripple them all.
The torpedo bombers were allocated months before the attack, before the shallow water problem was solved. As late as 4 November, during what has been referred to as “the dress rehearsal,”46 only 40% of the torpedoes leveled off at the correct depth. At this rate only 10 torpedoes would hit the battleline, perhaps two per battleship, which was sufficient to damage, and perhaps to cripple, but not to sink. Using Fuchida’s original guesstimate, there would be 16 torpedo hits on the battleline, two or three per target if evenly distributed. And again, that was enough to cripple, but not to sink.
If 80% hits could be expected, then each B5N Kate with a torpedo would be worth 0.16 of a capital ship. Twenty-four torpedo bombers, cumulatively, would be worth 3.8 battleships sunk out of six potential targets.
The planners originally allocated only crippling power against the battleships, not killing power.
Carrier Moorings Attack Group
The other 16 torpedo-carrying bombers, two groups of eight, were assigned to attack the carrier anchorages on the northwest side of Ford Island. The Japanese formal estimate was that three of the carriers were operating out of Pearl Harbor,47 although their intelligence agent’s reports would attest that rarely were all three in port together.