Attack on Pearl Harbor (15 page)

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:

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.

Three carriers were assigned to the Pacific Fleet,
Enterprise
,
Lexington
, and
Saratoga
.
Saratoga
was at San Diego. She had not been operating out of Pearl Harbor while in drydock at Bremerton. The intelligence officer’s reports would not have mentioned her presence since October.

The attack against the carrier moorings would involve a fairly easy approach along the length of the loch past Pearl City, with plenty of room to set up the attack and establish the proper release conditions. The approach would be at an angle so the targets would be foreshortened, reducing the target cross section by about 30%. The approach would pass several nests of destroyers, so surprise would be needed to avoid AA fire.

These 16 bombers represented 40% of the torpedo-armed bombers. The maximum number of carriers the Japanese could expect to find in port would be three, two more likely, fewer still considering the carriers spent a lot of time underway. At 40% hits, this group would be expected to score six hits, enough to sink two carriers; at 68%, ten hits, which could account for all three carriers or gut two; 82% would give thirteen hits, over four hits for each carrier assigned to the Pacific Fleet.

This allocation provided killing firepower against the carriers.

Weighting the Attack

The battleship anchorages might expose six battleships along battleship row. The Japanese assigned 24 aircraft to attack this group, four per potential target. The other group of 16 bombers would be attacking, at most, three carriers, more likely only two, for five to eight torpedo bombers per potential target. They maintained this overweight even after they received an intelligence report that none of the carriers were in port, in the hopes that the carriers might return.