Alan D. Zimm
Page 23
The second wave dive bombers had a difficult task trying to identify targets with the anchorage filled with smoke and a cloud layer at 3,500 feet, between their pitch-over attitude and their targets. They had to deliver their attacks through heavy AA fire from an awakened defense.
A Tactical Error? The Attack on Nevada
The second wave arrived to see Nevada underway and heading towards the entrance channel. The Japanese had hoped for an opportunity to sink a ship and block the channel.
Fuchida claimed that he considered taking command of the dive-bombers, but noticed Egusa setting up to attack Nevada. Fuchida had his pilot bank to give him a better look, and related that he thought, “Ah, good! Now just sink that ship right there.”31 This has to rank as one of the more foolish thoughts to come out of the battle.
There are several issues regarding this decision, and the conduct of the second wave dive-bombers in general:
1) Was the decision to attack Nevada appropriate?
2) Were their other target selections appropriate?
3) Was their bombing accurate?
4) Was it possible to block the channel?
Target Assignment
According to the planned prioritization of targets, the second-wave dive-bombers were to attack carriers first, followed by cruisers, then followed by battleships. Veterans recount that their targets were carriers. The 250kg GP bombs were capable of sinking carriers, possibly with as few as four hits.
If the torpedo bombers capsized any of the carriers, the dive-bombers were directed to hit the overturned hulls and reduce the ships to scrap. This was a bad decision. A sunken carrier would take more than six months to raise and recondition. If the war lasted longer than that, any bomb damage inflicted on a capsized hull would not add to the repair time. Such hits would require additional repair facility man-hours, but would not necessary extend the duration of the repair work. If Genda did not think of the idea, he surely approved.
The idea that dive-bombers were to attack sunken carriers was a bad planning decision that would not have contributed to achieving the mission of the attack. It is another reflection of the disparity between Yamamoto’s and Genda’s goals.
According to some testimonies, the second wave was on deck and preparing to launch when the aircrews received the word that the reconnaissance aircraft reported no carriers in Pearl Harbor. According to the prioritization scheme they should then have considered cruisers as their primary target; however, at least some of the aircrews were told just before launching to “hit the targets left over from the first wave,” meaning battleships. Forty percent did go after battleships, an inappropriate weapons-target match that did not contribute to accomplishing the attack’s objectives.
Targeting Decision Making and Bombing Accuracy
The second-wave dive-bombers’ target selection was miserable. GP bomb hits and significant DNMs (damaging near miss)32 tell a part of the story of what the dive-bombers attacked:
Only one hit and one DNM were achieved on the dive-bombers’ highest priority targets. None of these cruisers were sunk, and the other six were untouched. Seven hits and one DNM were achieved on battleships, 10% of the 78 bombs.33 Including all ships that were attacked (no matter how inappropriate), 15 bombs hit something of value, raising the hit percentage to 19%; the percentage improves to 24% if four DNMs are included.
Destroyers Cassin and Downes were in the same dry dock as Pennsylvania; the bombs that hit these destroyers were aimed at the battleship. This would reduce the “hit what was aimed at” percentage to 15%, with three hits in the category of “collateral damage.”
Why aircraft attacked the destroyer Shaw is unknown. It is possible that the destroyer and floating drydock combination was misidentified as a cruiser or battleship. Recall that the Japanese dive-bombers were to attack at about a 55-degree dive angle beginning about a half-mile from the target. At that angle, visually the sides of the floating drydock would merge with the sides of the ship, particularly in the dramatic shadows of early morning light. With both painted grey, the pair would very much have the bulky look of a battleship when viewed through cloudy skies.
It is also possible that the bombs that hit Shaw were actually aimed at Nevada as she passed by the floating drydock in her sortie down the channel.
Studies of German dive-bombing accuracy by Ju-87 Stukas (an aircraft very much like the D3A Val) under combat conditions found a circular error probable (CEP) on the order of 30 meters, or about 90 feet. Battleships were on the order of 600 feet long by 90 feet in beam, while the Americans’ larger 10,000-ton cruisers were approximately 600 feet long with a 65-foot beam. A 50–60% hit rate ought to be expected if the Japanese dive-bombers’ accuracy were comparable to that achieved by the Germans. In practice sessions the Japanese had scored 50–60% hits on a target the size of a small battleship underway at 14 knots.34
The 1941 edition of the NWC Maneuver Rules specifies that dive-bombers against a stationary, battleship size target would obtain 16% hits, close to what the Japanese actually achieved. A 1951 OEG study changed that rate to 20%, using a CEP under “ideal combat conditions” of 175 feet, based on the wartime performance of US dive-bombers.
At Pearl Harbor, the dive-bombers’ accuracy was well below Japanese expectations, in fact, below the historical performance of dive-bombers in the Pacific over the entire war, and their target selection was poor. From the hits and near misses that were observed, it is likely that approximately 31 of the dive bombers assigned to ship targets went after the battleships Pennsylvania, California, and Nevada, rather than cruisers—40% of the dive-bombers wasted their weapons in inappropriate weapon-target matches.
The ultimate ignominy was that the dive-bombers were out-scored in hit percentage by the level bombers, who before the battle were expected to get a hit rate about a quarter of that expected of the dive-bombers.
Level of Effort Against Nevada
Egusa’s decision to use dive-bombers to attack Nevada was an inappropriate weapon-target match. The 250kg GP bomb was not a battleship killer. It did not have the penetration to breach the citadel or reach the magazines or engineering spaces, and was not a direct challenge to the ship’s watertight integrity. The chances that these weapons would sink a battleship in the channel were exceptionally low.
If the basic decision to attack the Nevada was bad, it was made worse by the level of effort that the flight commanders allocated. Approximately 14 D3A Vals (possibly as many as 18) attacked Nevada. Under training conditions this might get eight hits. The dive-bomber commanders would have no way of knowing that Nevada had been previously hit by a torpedo, so they had to expect to sink the ship on their own. Were eight 250kg bomb hits sufficient to sink a battleship?
The answer is a resounding “no.” The Japanese knew that GP bombs had no chance of sinking the ship, and the Americans’ assessment was the same. Striking Power of Air-Borne Weapons, a US Naval Intelligence document, makes this assessment of GP bombs v. battleships: “Even though fires and extensive structural damage above the armored deck result from the employment of G.P. bombs, sinking is not to be expected except when a comparatively large number of such hits are received.”35 In the NWC Maneuver Rules of June 1940, 64 500-pound GP bomb hits would be needed to sink Nevada, 55 in combination with a single aerial torpedo hit. In this case the deterministic model of ship damage is appropriate, since the bombs did not have the penetration to get into magazines or engine rooms.
The Japanese expected that it would take 18 dive-bombers to sink a fragile carrier.36 How, then, could they expect to sink a tough battleship using only 14?
The Japanese dive-bombing attack on Nevada was a wasteful half-measure. Even if all the bombs had hit, 14 hits were well short of what they must have known was needed. The attempt to sink Nevada in the channel was a waste of ordnance that could have been better employed against targets more vulnerable to their effects.
A charge of negligence has to be directed against the authors of this hare-b
rained idea—Fuchida (who briefed the idea), Genda (who allowed the idea to be briefed), and doubly again against Fuchida who, as the on-the-spot strike commander, allowed it to proceed.37 Fuchida should either have cancelled the effort, or poured on sufficient dive-bombers to have at least a chance of sinking the ship. The dive-bomber crews or commanders ought not be blamed—they operated as briefed, although they should have known that the numbers committed were inadequate.
The very idea that sinking a ship in the channel would bottle up the Pacific Fleet was a shocking miscalculation. This myth will be more fully explored in Chapter 10.
But, how can the decision to attack Nevada be considered poor when the damage inflicted by the dive bombers directly contributed to sinking the ship?
Sinking Nevada
The Japanese benefited from an extraordinary chain of circumstances in their attack on the Nevada.
Two GP bomb hits contributed flooding, something that ordinarily would not be expected. One passed through the forecastle and out the hull to explode directly alongside, punching in side plates and leaving two wide cracks, one 25 feet long and the other 18 feet long. While this seems dramatic, flooding from this hit was limited to the outermost torpedo defense void. A second bomb passed through the forecastle and out through the bottom to explode under the hull, creating a hole six feet in diameter.38 This caused more flooding, but it was flooding outside the ship’s armored, watertight citadel, and as such should not have been lethal. This was the extent of the flooding directly caused by the 14 GP bombs. It was not enough to sink the ship. Many, many more hits like this would have been required to give the immediate, large scale flooding needed to sink a battleship in the channel.
The ship would have remained afloat had not three other factors come into play. Nevada succumbed not to Japanese bombs but to poor material condition, critical design flaws, and a massively significant damage control mistake.
Starting from the initial attack, Nevada was hit by a single torpedo forward port side between the two forward main battery turrets. The innermost torpedo bulkhead held, but leakage at the seams and butts caused flooding below the first platform. At this point the poor material condition factor came into play. Manhole covers to the torpedo defense voids and some fuel tanks were either loose or were sprung by the torpedo hit, allowing oil and water to flood the third deck. As the ship settled oil began shooting up out of the fuel tank sounding tubes, past caps that ought to have been sealed with effective gaskets. An initial five degree list was corrected by counterflooding. But the flooding was being contained, and this hit would not have sunk the ship.
After getting underway the ship was hit by five 250kg GP bombs. Two of the hits caused additional flooding forward, as mentioned above. The other bombs started a large fire in the forward superstructure. One bomb passed the forward gasoline storage tank to explode just under the bottom of the hull, opening a six foot hole in her plates. Gasoline leakage and vapors almost immediately ignited in the forward part of the ship near the magazines. The forward superstructure was engulfed in flames, and by the end of the battle the foremast structure containing the bridge was destroyed.
Because of this fire, the forward magazine was ordered to be flooded. Then the next factor came into play. Somehow the word was passed to flood the after magazine as well. These two flooded magazines put a huge tonnage of water inside the armored citadel, and the ship settled deep in the water.
Then the last factor came into play, two design flaws. The first was that the second deck was not watertight. As portions of the non-watertight second deck were submerged the flooding became progressive and compartments were flooded from above. The efforts of the damage control team were then stymied by the ship’s poor material condition. According to the ship’s war damage report, the crew was in a “losing fight against water spreading through boundaries and fittings which should have been watertight but actually were not.”39
For example, the Main Battery Plotting Room was one of the most protected spaces in the ship, five decks below the main deck at the bottom of the armored conning tower tube and inside the citadel. It escaped damage during the attack. Five hours after the last bomb had been dropped water started to enter through a watertight door and began streaming down from the overhead, and the compartment flooded.
Many similar deficiencies caused inexorable progressive flooding. For instance, sounding tubes in some crew spaces led down into fuel tanks. These tubes were capped with a threaded plug seated against a gasket. Many of the gaskets were either cracked or missing, or the cap missing altogether. When the fuel tanks were flooded by torpedo hits and pressurized as the ship settled in the water, the result was a fountain of fuel oil gushing out of the sounding tubes.
Throughout the ship watertight doors were not watertight and stuffing tubes for cable and piping runs leaked.
Then, the second significant design flaw frustrated all attempts to keep the ship afloat. The ship had a centralized ventilation system called the “Bull Ring” where the main ventilation air intakes were located. Air from the Bull Ring was distributed throughout the ship, with ventilation ducting piercing many watertight compartments. There were inadequate closures in the ventilation systems, so when the Bull Ring flooded, it distributed water throughout the ship, outside and inside the armored citadel.
Flooding progressively compartment by compartment, the ship eventually settled onto the mud.40
The Japanese objective of disabling Nevada for at least six months was thus achieved. Nevada was drydocked on 14 February 1942, and afterwards sailed under her own power to the Puget Sound Naval Shipyard on 22 April 1942. She was revamped and modernized, her old superstructure stripped off and an entirely new superstructure built, along with a greatly augmented AA battery and changes to correct the ship’s poor internal watertight integrity.
Nevada could have been repaired and returned to service in only a few months, albeit without many of the modernizations. The modernization took longer because her return to service was given a low priority, as the shipyard was directed to concentrate on new construction, battle damage repair, and modernizations for cruisers and destroyers. Plus, the battleships were not expected to be needed for some time. American prewar planning had always expected the decisive battleline engagements to occur near the Philippines or the island chains close to Japan. This was not anticipated to happen in 1942. Forward deployment of battleships would also require a robust logistics chain, again something that would not be established in 1942. So, repairs to Nevada could wait.
Nevada was back to sea in December 1942, one year after the attack.
Was the decision to attack Nevada with dive-bombers a good decision? A superficial analysis, based on the result–one sunken battleship–would intimate that it was. Nevada would not have sunk if she had not been hit by those five GP bombs, which caused the fire, which caused the magazines to be flooded, which caused the ship to settle and flood the second deck and the Bull Ring, which caused the progressive flooding which sank the ship.
However, the Japanese had no way of knowing that such a progression was possible. There was no way they could incorporate those factors in their decision process. The dive bombers’ attack, under any reasonable military criteria, ought to have been inadequate to sink the ship, by criteria used by both the Japanese and the Americans. The fact that the bomb hits triggered a chain of event that inflicted damage far out of proportion to any reasonable expectation was a result of factors that the Japanese could not reasonably predict.
Consider a man who wanted to start a farm, and so he decided to buy a piece of desert land. He should have known that he could not grow crops on parched land. Was it a good decision? Then, while plowing the ground to plant his first crop he strikes gold. The unexpected event does not make the original decision to start a farm in the desert a good decision.
The dive bomber’s success against Nevada, however unexpected, was the second wave dive bombers’ shining moment. It achieved success by a remarka
ble string of unlikely occurrences. Lefty Gomez once said, “I’d rather be lucky than good,” a sentiment in this case seconded by the Japanese dive bomber pilots.
Similarly, the other dive bomber attacks against other battleships were also bad decisions. Absent the factors that made the attack on the Nevada successful, those other attacks achieved what would be expected, that is, they achieved almost nothing, little more than nuisance damage to the heavily-armored ships. Superstructure damage such as was inflicted upon Nevada made for spectacular photographs, but essentially could be repaired with new sheet-metal and replacement electrical wiring. It was damage that could not be expected to put a ship out of the war for any significant period, and did little to contribute to the objective of the attack.
In Nevada’s case, there was effectively no chance that the ship could have been sunk in the channel and zero chance that the ship could have been sunk by five or even fourteen 250kg GP bombs. It was the design flaws, poor material condition and damage control errors that sank Nevada, not the Japanese dive bombers. The proper decision would have been to put those five hits on two cruisers which, with only a smidgeon of good fortune, would have put two cruisers on the bottom of the harbor.
Cruiser Targets
Cruisers were vulnerable to GP bombs. During World War II, nine Allied cruisers were sunk by GP bombs. A single bomb hit on a cruiser would, on average, require six to seven weeks of shipyard repair; one 500kg (1,102-pound) bomb hit on the British cruiser Suffolk forced the ship to be beached, and she was out of action for eight months.
There was a very lucrative grouping of cruiser targets available. In the Navy Yard, New Orleans, San Francisco, St. Louis, and Honolulu, all modern, powerful 10,000-ton cruisers, were crammed into a very restricted space. Bombs dropped into the Navy Yard piers area could hardly miss hitting something of value—a ship, a pier, quays, tugs or yard craft, floating cranes, or the industrial facilities. In the face of this crowding, the number of 250kg bombs that splashed in the water causing no damage was remarkable.