Attack on Pearl Harbor (30 page)

(15) Torpedo Hits: Claimed and Actual

The actual number of hits is uncertain. For
Oklahoma
, the whole side of the ship was nearly completely blown open, making it difficult to pinpoint individual detonations. Explosion effects overlapped. Some have asserted that additional torpedoes must have entered the ship through holes blasted by previous torpedoes. This did not occur. If a torpedo had penetrated into the ship though a hole blown by a previous torpedo, then the entire force of the explosion would have been contained inside the ship. The expanding gas bubble would have caused massive internal damage, to include lifting up the armored deck directly above the explosion, and warping belt armor plates out away from the ship instead of in an inward direction. No evidence of such damage was evident.

Witnesses reported nine torpedo hits on
West Virginia
. The salvage engineers reduced this to seven: four deep hits amidships, two that hit above the ship’s belt armor as the ship listed, and a hit on the rudder.
¹⁰

Allegations of a hit on
Arizona
are unsubstantiated. The Japanese did not claim any torpedo hits on
Arizona
.

The minimum number of hits shown in the chart, 19, is likely accurate.

The BDA Report indicates that torpedoes were directed at only six ships: four battleships, one cruiser, and
Utah
. Four battleships and four cruisers were located in positions vulnerable to torpedo attack. Torpedoes were directed at four of the eight (50%) susceptible priority targets. Five (63%) of the eight were hit, including
Raleigh
hit by a torpedo aimed at
Utah
. Attacking only half the accessible priority targets was not a good performance.

Fuchida overestimated the number of hits on
California
(three claimed, two actual),
Oklahoma
(12 claimed, five actual),
West Virginia
(nine claimed, seven actual),
Helena
(five claimed, one actual), and
Utah
(six claimed, two actual). But these errors did not result in an overestimation of the net damage in the final assessment. The differences in the BDA report and the actual results could be attributed to unanticipated vulnerability of the ships and some external events.

California
would not have sunk except for many Zed closures that were still open. General Quarters and Material Condition Zed had not yet been fully set when she was hit. She had open and loose manhole covers to various voids, with six covers on her double bottom removed and 12 loosened.
¹¹
In addition, burning oil swept down on her after
Arizona’s
explosion, and she was temporarily abandoned, interrupting damage control efforts at a critical time.

Nevada
sank from only one torpedo hit and five GP bomb hits due to poor material condition, design flaws, and a significant damage control blunder.

The BDA report overestimated the number of torpedo hits but underestimated the number of battleships sunk.

A significant error was the assessment of hits on
Helena
: five torpedo hits were claimed, which would have gutted any cruiser.
Helena
took only one torpedo hit in the forward engine room. Excellent damage control minimized the flooding. She was out of the war for six months under repair at California’s Mare Island Naval Shipyard.

The report of 36 torpedo hits exceeded their pre-attack expectation of 27 hits (67%), and also their best score during training, 82.5%. The individual carriers claimed only 33 hits based on aircrew reports. It is difficult to imagine how a post-attack evaluation team justified increasing the claim—they mainly would be working off photographs, which might indicate that a ship was torpedoed, but not how many times, as the damage would be underwater, invisible to post-strike photographs. It might have reflected a simple decision to credit all the surviving torpedo bomber aircrews with hits, along with one to a crew that was shot down. In this way no stigma of failure would be attached to any of the surviving aircrews, a very Japanese behavior.

More significantly, this shows that the BDA team was willing to adjust the combat results away from what was reported by the aviators, and adjust it in a positive direction. Later in the war it was recognized that aviators’ reports generally overestimated the results of their attacks, and on the Allied side it was usual for post-action assessments to discount claims by 50% or more. Here, the staff gave the aviators credit for more than they claimed.

The Japanese post-war official history claimed 23 torpedo hits on battleships, eight more than occurred. It assessed one hit on
Nevada
(one actual), two hits on
Arizona
(zero actual), two hits on
California
(two actual), and nine hits each on
West Virginia
and
Oklahoma
(seven and five hits, respectively).
¹²
With the combined 11 hits on
Utah
and
Helena
, the official history only reduced the total hits claimed by two.

AP Bombing BDA

The BDA report gave the horizontal bombers credit for 13 hits with 800kg AP bombs, or a hit rate of 26%. This is well above the eight hits expected. All of the hits were assessed against battleships but for one hit on a ship, identified as an oiler, in the location of the repair ship
Vestal
.

American ARs and post-battle damage inspections suggest ten confirmed AP bomb hits, eight against battleships and two against
Vestal
.

Arizona

Some sources assert that eight AP bombs hit
Arizona
. These claims draw from variety of sources, including crewmembers and officers of the
Vestal
and official Navy reports. Most of these hits supposedly landed amidships and forward, where the extensive damage from the magazine explosion and fire precluded confirmation.

(16) AP Bomb Hits: Claimed and Actual

Human testimony on the number of hits observed during a battle is notoriously inaccurate. Hits might be double counted, or secondary explosions counted as additional hits.

Either two or three formations dropped 10 or 15 bombs on
Arizona
. With the spread of the formations exceeding the dimensions of the target, multiple hits by the same formation on the same part of the target would have been nearly impossible.

The BDA report claimed four hits on
Arizona
, assessing “serious damage.” The ship forward of her,
Tennessee
, was assessed as “sunk” from three AP bomb hits. Both ships were shown on fire.

A detailed examination of the level bombers’ attack on
Arizona
was made by De Virgilio incorporating Japanese testimony, the formation dimensions, and approach direction into a computer analysis of the ballistic bomb patterns. He also reexamined the damage reports. His analysis convincingly shows that only two bombs hit, one on the quarterdeck and one forward that detonated the magazine.
¹³

AP Bomb Hit Percentages

In
Lessons
the Japanese claimed 13 hits out of 35 bombs (37% hits). 35 aircraft were used in the calculation rather than the 48 bombs dropped or the 50 aircraft assigned to level bombing, improving the percentage. The post-battle report notes that “These figures were concluded only from those which were accurate.”
¹⁴

If Fuchida indeed had a hand in the writing the report, as the leader of the level bombing effort and a level bombing specialist himself, he was psychologically disposed towards, and had a personal stake in seeing the results put in a favorable light. The author of the report evidently considered the bombs from three formations (15 aircraft) as “not observed,” and omitted them from the calculation, thereby lowering the denominator and improving the percentage.

This is the second place in the report where figures appear to have been manipulated to magnify the results (the first being the inflated torpedo hit percentage). In this case, the manipulation is minor and justifiable.

The number of hits claimed in the BDA Report was overstated by over 60%—13 hits claimed on battleships, eight hits actually achieved. Four battleships were claimed hit, and four battleships were actually hit. All three inboard battleships were hit.

Overall, the level bombers delivered a superb bombing performance, and the subsequent assessment was creditable.

Effectiveness of the 800kg Bombs

Except for the hit that detonated
Arizona’s
magazine, the AP bombs inflicted remarkably little damage. When the lower body of the bomb was shaved down to lighten the weapon, it weakened the bomb such that impact at an angle could crack open or deform the projectile. Six of the ten hits were either duds or low-order detonations.

A bomb that hit
Maryland
detonated on an awning strung above the forecastle; one that hit
Vestal
penetrated entirely through the ship and detonated on the bottom of the harbor. These hits indicate that the delay fuze functioned irregularly.
¹⁵

Other than the hit on
Arizona
, the most serious hit was on the top of main battery turret 3 on
Tennessee
. The bomb hit the turret top armor at an overlapping joint between armor plates. The plates were forced apart and the bomb was deflected. The aft section of the bomb slapped against the overlapping roof plates, crushing the lower body and breaking it apart. The base plug containing the fuzes probably separated. The impact ignited (rather than detonating) the explosive. Damage was limited to a rammer in one of the turret’s three gun chambers.

West Virginia
took a similar hit, penetrating the six-inch roof armor. “The nature of the penetration indicated defective material,” according to the Navy damage report. This bomb, too, was a dud, only damaging a loading slide.
¹⁶

As for
Arizona’s
magazine explosion, the US Navy investigation was predicated on the belief that the bomb did not have the capability to penetrate into the magazine.
¹⁷
Instead, they theorized that the bomb exploded on the second deck and ignited something flammable inside the ship such as powder left outside the magazine. The hot gasses were believed to have flashed through an open armored hatch leading to the black powder magazine, which then detonated.

This sequence is highly unlikely. For it to work, black powder had to be left out in an unsecured passageway outside the magazine, and a hatch to the magazine left open. In a safety-conscious Navy, doors to magazines were just not carelessly left open over a weekend. Magazine doors were shut and locked unless absolutely necessary. All ships had Sounding and Security Patrols that checked magazine spaces hourly, recording temperatures and ensuring that all hatches are locked and that bulkheads of locked compartments are not warm to the touch, a possible indication of a smoldering fire. Magazine temperatures are taken hourly. Having a magazine door open and powder scattered about on a Sunday morning before colors (before the beginning of normal working hours) would have been inconceivable. The evidence throughout the fleet that day testifies that sailors were forced to break open locked magazines to get the flow of ammunition started.

This explanation was unchallenged by ship’s personnel because the gunnery department personnel responsible for the forward turrets and magazines were wiped out in the explosion.

Even if a hatch had been open before the attack, there was between eight to 13 minutes from the beginning of the attack for the ship to set General Quarters and Material Condition Zed before the bomb hit. All the turrets had reported manned and ready with Zed set prior to the explosion, as had the after magazine.

A much more likely scenario has been developed independently by three analysts, De Virgilio, Okun, and Aiken. Their assessment is that the bomb did have sufficient armor penetration capability to penetrate into the forward powder magazines. A movie camera recording the
Arizona
at the time of the explosion records a seven second delay from when the bomb hit and the magazine exploded. The sequence of events on the film suggest that the powder in one of the starboard magazine spaces began to burn and explode, building up pressure and spreading hot gasses to the other starboard powder rooms, then crossing to the port side, and eventually detonating the port powder rooms. Physical evidence on the sunken hull is consistent with this scenario.
¹⁸

The Navy investigation team, largely made up from Bureau of Construction and Repair naval architects, looked for an explanation that would be consistent with their assumptions. They were predisposed to believe their original design calculations that the magazine was sufficiently protected and that AP bombs could not penetrate to the magazines, so they looked for how else the explosion could have occurred. They settled on an explanation based on operator error rather than a design error. Admitting that the bomb penetrated into the magazine would be an admission that the magazine was inadequately protected, something that they simply did not believe from the outset. They also explained the penetration of
West Virginia’s
turret top as due to defective armor. This was not a cover-up or conspiracy, but rather another example where incorrect initial assumptions and an inflexible mindset biased an investigation.

Assessment: Level Bombers’ BDA

The most serious disconnect between the BDA and the actual results were in the assessed fate of two of the three inboard battleships. The BDA had one battleship sunk and two with serious damage.

Arizona
was indeed sunk, but
Tennessee
and
Maryland
suffered only minor damage. The BDA indicated that all three battleships would likely be unavailable for six months.
Tennessee
and
Maryland
were available within weeks, sooner if necessary.

This appears to be a case where Fuchida overrepresented the damage attributed to his level bombers. He could have assumed that a lack of bomb detonation signature meant that the AP bombs had penetrated deeply into the target, making crippling damage likely. Considering that he claimed that he was the one who insisted that level bombers be included in the attack, and that he himself led the level bombers, he was certainly psychologically predisposed to see crippled battleships as a result of his personal efforts.

Had it not been for the one fortuitous hit, the level bombers would have given a very poor return on their investment.

The postwar Japanese Official History downgraded the claimed hits to eight: one on
California
(none actual), one on
Maryland
(two actual), two on
Tennessee
(two actual), and four on
Arizona
(two actual).
¹⁹

Assessment:

Dive-Bombing Against Fleet Units BDA

Hits Claimed and Target Classification Accuracy

The individual reports from the carriers submitted to the flagship immediately after the attack complained that most of the second-wave dive-bomber attacks could not be properly assessed due to smoke obscuration.
Akagi
claimed an unspecified number of hits on a battleship and one hit on an
Omaha
-class cruiser.
Kaga
claimed that “most” bombs hit
California
and two other battleships.
Soryu
and
Hiryu
submitted a combined report
²⁰
claiming five hits on two light cruisers and one on a destroyer in drydock. The reports suggest a combined total of 20 to 30 hits.

The BDA Report claimed 49 hits for 63%. Almost a year later,
Lessons
changed this to 38 hits out of 65 bombs (59%). These percentages were in line with expectations from training: 60% hits from 78 bombers gave an expectation of 43 hits.

The air groups’ performances were very uneven: flagship
Akagi
was credited with one hit out of 15 or 18 bombs (6%),
Kaga
with 8 definite hits and 13 probables out of 27 (78%),
Soryu
14 hits out of 17 (82%), and
Hiryu
a remarkable 15 hits out of 16 bombs (94%). This totaled 38 hits (49%) with 13 probables. In Fuchida’s BDA report to the Emperor, probables were not reported—11 probables were converted into hits, and two dropped.

Akagi
was credited with a very low performance compared to the other carriers.
Akagi
was the flagship. This is extraordinary.

Flagships characteristically were the best performing ships in the fleet, the “Battle E” winners, the best of the best. While some of this elevated reputation can be attributed to flag staff members who give inflated grades in exercises to the ship in which they live and serve, it also can be attributed to the fact that flagships are “high profile” ships that get their pick of high-performing officers and men. Flagships were under constant scrutiny from the flag and his staff, and so were motivated to maintain top performance. This represents a cultural characteristic in all the major navies—flagships generally are the shiniest, and the best performers.

Assigning
Akagi’
s aviators a miserable hit percentage was a seismic turnabout. Experienced naval officers would note this with shock. The best dive-bomber aircrews were given the lowest scores. They were on the ship where the assessment was being formulated, and so were available for questioning. It would be hard to misrepresent their results. The huge gap between
Akagi’s
results and those attributed to the others is a huge anomaly.

In this context it should be noted that
Akagi’s
torpedo bombers were the ones that likely scored the majority of the 11 effective hits on Battleship Row, confirming that flagship aviators generally perform well.

The BDA Report claimed a target selection biased against battleships. No hits were claimed against priority 1 targets, carriers (granted, there were none in port, but at least
Utah
was not claimed to be a carrier). 14 hits were assessed against seven different cruisers (priority 2), 27 hits against five battleships (priority 3), and 8 hits against auxiliaries and smaller ships (priority 4 and lower). The chart shows how these hits were distributed, along with the number of aircraft reportedly attacking each target.
²¹

The BDA Report has flaws in target identification.
Dobbin
, a 12,650-ton destroyer tender, was identified as a cruiser, as were destroyers
Dale
and
Shaw
.
Shaw
was correctly identified in the flyers’ report as a destroyer in drydock, but the BDA report promoted her to a cruiser.

Overall, only five of the claimed hits (10%) had their targets misclassified. While photographs were being taken by the attackers, they probably did not get 100% coverage of all the targets that were attacked, and had to rely to some extent on aviators’ reports.