by Attack on Pearl Harbor: Strategy, Combat, Myths, Deceptions
After Fuchida’s initial report, the aircrews were individually debriefed, recording their assessments as to what they attacked and their results. Admiral Kusaka, “a man of the highest integrity who would scorn to embroider,”1 relates how “on each carrier a minute examination was conducted against the claimed result of the attacks, gathering the returned fliers. Its results were successively sent to the Akagi.”2
On Akagi,
Fuchida instructed all officers to develop their attack photographs at once for study in preparing a final assessment of damage inflicted. Courier planes from the other five carriers landed aboard Akagi, bringing data and photographic film from the attack units. By late afternoon he had all the prints. The flight leaders studied them most of the night, and the next morning Fuchida turned in his battle report.3
On 17 December, while still at sea, Nagumo transmitted a preliminary Action Report. Torpedo hits were estimated at “over 35 out of 40.”4 The report estimated four battleships, two heavy cruisers, and one tanker sunk; “one type uncertain (sunk by torpedoes)”;5 two battleships, two light cruisers, and two destroyers with “heavy damage;” and two battleships and four light cruisers with “small damage.”6 The biggest change over Fuchida’s initial verbal report was that the number of battleships sunk was doubled.
Eight cruisers were claimed hit. Two were reported sunk by a combination of torpedoes and 250kg GP bombs; the other six were assessed as damaged by a total of nine 250kg GP bomb hits.
A total of 26 250kg bomb hits are mentioned specifically, along with “several” 250kg hits against a Maryland-class battleship.
The report would go straight to the top:
Most signal honor of all, the Pearl Harbor raiders learned that the Emperor wished to hear the account of the operation directly from those who had led the attack…. Fuchida and Shimazaki [the leader of the second wave] worked together on their reports. Fuchida would relate to His Majesty the story of the strike on the United States ships; then Shimazaki would brief Hirohito about the attack on the air bases. Because Shimazaki was far handier with the controls of an aircraft than with brush and paper, Fuchida had to write both reports.7
Four days after returning to Japan, on 27 December Commander Fuchida briefed the Emperor. He used a top-secret map with beautiful brush-strokes and vivid colors, which showed in detail the position of the ships, the number of torpedoes hitting each ship, and the numbers of AP and GP bomb hits. The chart identified the ships by type or class, but not specifically by name. This will be referred to as the BDA Report.8
On the chart, damaged ships were classified either as “sunk” (symbolized as “X” on the chart); “serious” damage (“///”), meaning impossible or very difficult to repair; “moderate” damage (//), meaning possible to repair; and “minor” damage (“/”). Symbols identified the location of each torpedo, AP or GP bomb hit.
Destroyers Dale and Helm were misidentified as class “B” cruisers, repair ship Vestal was misidentified as an oiler, and tender Dobbin was misidentified as either an “A” or “B” class cruiser. The movements of Nevada and Oglala were shown, but the escape of Neosho was not. Otherwise, the depiction of the ships and their locations was remarkably accurate.
The left portion of the next table contains a summary of the information contained on Fuchida’s BDA report. The right portion shows the actual damage inflicted taken from official reports and two published accounts of the salvage efforts.
Torpedo BDA
Fuchida’s BDA briefing chart shows an arrow symbol representing “torpedoes.” There are 36 torpedo symbols shown on the chart.
In Lessons, the Japanese stated that 40 torpedoes were launched, of which 39 ran and 36 hit for 90% hits.9 The initial assessment made at sea claimed “over 35” hits. The torpedo hit percentage claimed was greater than the best hit percentage (82.5%) achieved during pre-attack training.
According to Kusaka, the battle reports from the individual carriers claimed 33 torpedo hits (Akagi 11, Kaga 8, Soryu and Hiryu combined for 14). How Fuchida and his assessment team arrived at 36 hits is unknown. 36 torpedoes were not launched—four aircraft were shot down before dropping, and one jettisoned its torpedo. Three hits were reported against cruisers, while Fuchida’s report claimed five, all on Helena.
Chart 15 shows the hits claimed in the BDA report, shown in the dark circles v. the actual hits, shown in the light circles.
The BDA Report assessed 25 torpedo hits against four battleships. Of them, 21 (84%) were concentrated against only two, Oklahoma and West Virginia. The report honestly records the six torpedoes wasted against Utah, and the BDA chart identifies her by name. All six are assessed as hits. The torpedo that hit Raleigh was evidently unobserved.
JAPANESE BATTLE DAMAGE ASSESSMENT
ACTUAL DAMAGE INFLICTED
(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 base
d 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, bui
lding 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.
