by Attack on Pearl Harbor: Strategy, Combat, Myths, Deceptions
The destruction of the power plants supplying electricity to the Pearl Harbor base would have been a problem, but a temporary problem. It would not have had the strategic effects implied by Morison and Hart.
Conclusions: Attacking Pearl Harbor infrastructure
Admirals in the Pacific learned the great value of the Pearl Harbor Navy Yard throughout the early months of the war. It restored damaged battleships and two torpedoed cruisers and maintained the fast carrier task forces. In one celebrated case, without the Pearl Harbor Navy Yard, Yorktown would not have been ready for the Battle of Midway. Certainly admirals would shudder at the thought that the capability might have been taken away in the Japanese attack, as did Admiral Hart and Morison in print.
However, they did not consider what could have done to correct the problem. They did not consider the considerable alternative capacity in the repair ships afloat. Later in the war front line ships were well serviced by these repair ships and tenders far forward of Pearl Harbor. There is no reason why they would not have proven their worth earlier had the Pearl Harbor Navy Yard been incapacitated.
A Japanese third-wave attack simply would not have the firepower to inflict debilitating damage on the Navy Yard. Considering the available restorative capacity on the island, afloat and ashore, military and civilian, any damage could be put to rights in a short time.
Statements that a third wave attack against the shipyard would set the war in the Pacific back by a year are gross exaggerations. These targets were, indeed, as expressed by the Japanese Admiral Hara, “mere secondary objectives.”65
Attacking the Fuel Oil Storage Tanks
The other target mentioned prominently is the fuel farm. Admiral Kimmel considered that the oil storage would have been an even more lucrative target than the warships: “… if they had destroyed the oil… it would have forced the withdrawal of the fleet to the coast because there wasn’t any oil anywhere else out there to keep the fleet operating.”66 Goldstein, Dillon and Wenger claimed that not only would the destruction of the oil tanks have “crippled the entire Pacific Fleet,” but they extended the hyperbole by stating, “Their destruction would have rendered useless every military and naval installation in the islands.”67 Willmott, Tohmatsu and Johnson have stated that with the destruction of the oil “an intact Pacific Fleet, even if it suffered not as much as a single loss, would have been forced to withdraw to San Diego.”68 Admiral Nimitz is also on record as saying, “We had about 4.5 million barrels of oil out there and all of it was vulnerable to .50-caliber bullets. Had the Japanese destroyed the oil, it would have prolonged the war another two years.”69
Genda wrote after the war that the question of destroying the fuel tank farms only arose after the attack. “That was an instance of being given an inch and asking for a mile.”70 The objective was to destroy warships. Oil tanks did not enter into the original concept, and for good reason—when considered as a bomb hauling problem, Kido Butai’s aircraft simply could not transport sufficient ordnance to destroy everything it would have liked. The oil storage was never even on their agenda. Besides the well-known Japanese dismissal of logistics concerns, all the destruction of the oil storage would do from their viewpoint is to delay the American counterattack. If it was indeed a two-year delay as suggested by Admiral Nimitz, that would be about the time when the Pacific Fleet would have been greatly augmented by new construction and would have greatly outnumbered the Japanese fleet. A long war is not one the Japanese wanted to fight or thought they could win.
Given that, it remains to test if the Japanese had the capability to destroy the fuel tanks.
The Pearl Harbor fuel farms consisted of 54 major fuel tanks constructed on small hills and slopes in two complexes, one between the shipyard and Hickam Field, and the other above the submarine base. There were also aviation fuel storage areas on Ford Island with pipes and manifolds leading out to the Ford Island fueling pier berth F-4, where the oiler Neosho was moored at the beginning of the attack. The largest tanks had a capacity of over 10,000 tons of fuel; the total storage capacity of ships’ fuel was 563,000 tons. To place this in context, a full fuel load for the surface combatants in harbor the day of the attack (eight battleships, eight cruisers, and 30 destroyers) would have been about 61,000 tons.
Prewar, Pearl was serviced by three commercial tankers making a continuous shuttle from the California oil fields. They were delivering about 40–50,000 tons of fuel monthly, enough to meet the fleet’s training needs plus build up reserves to near capacity. The Pacific Fleet had a total of 11 tankers, of which four were fitted for underway replenishment.71
In addition to the surface tanks, a tremendous underground fuel storage project was begun in late December 1940. Called the Red Hill Underground Fuel Storage Facility, this secret installation eventually had 20 vaults with a total capacity of 5,400,000 barrels of fuel oil and 600,000 barrels of diesel for a total of 818,200 metric tons of fuel, over doubling the fuel storage at Pearl Harbor. The first of the vaults came on line on ten months after the attack, and the project was completed in September of 1943.
Destruction of Oil Storage by Machine Gun Fire
Nimitz believed that the fuel tanks could be set afire by .50-caliber machine gun fire. If this is true, failure to do so represented a significant lost opportunity for the Japanese.
The oil was stored in surface tanks with metal sides and a light conical roof to keep rain out. A flat top floats so there is no vapor space above the fuel, preventing explosive vapors from accumulating and keeping oxygen away from the fuel. The sides of the fuel tank were .75 of an inch to about 1.5 inches in thickness, tapered to increasing thickness near the bottom.
The Japanese aircraft did not carry .50-caliber machine guns. Their standard aircraft machine gun was the 7.7mm machine gun, a close relative of the British .303 machine gun.
Besides two 7.7mm machine guns, the A6M Zero carried two low-velocity 20mm cannon with 60 rounds per gun. The 20mm shell was designed to explode on contact with very light aircraft surfaces, thin aluminum or fabric, and so would not penetrate the tank sides. If hitting the roof, it would explode and hole the roof but likely would do little against the floating top. Fragments might penetrate the floating top, but would not have sufficient energy or any oxygen to ignite the fuel.
For fuel oil or diesel, a bullet would not ignite the fuel. If the bullet penetrates below the liquid level there is no air to support combustion. Even if there was oxygen, the flash point of the fuel is too high, and any bullets hitting a pool of fuel would not carry enough energy to raise any significant volume of fuel to temperatures where ignition could be sustained.72
Regarding penetration of the fuel tanks, Edward Rudnicki, a US Army ammunition expert, relates:
WW2-era rifle-caliber AP typically penetrated its own diameter or a bit more [of metal plate]. The German 7.9x57mm AP was good for 10mm at 100m at 0 incidence, and the US .30 was good for a full half inch. But both of these were more powerful cartridges than the .303 British, which is what the 7.7mm IJN round is. But you’d need API [armor-piercing incendiary ammunition] to ensure fuel ignition, and I don’t think [the Japanese] had API. Unfortunately because the IJN 7.7mm is the same as .303 it’s hard to find info on the Japanese loadings, but I do note that the IJA’s 7.7x58mmSR did not have API, but rather separate AP and I [incendiary] loads.73
The idea the Japanese could have achieved a “cheap kill” by machine-gunning the fuel storage tanks is a myth.74
Destruction of the Oil Storage Tanks by Bombing
Assumptions that the Japanese attack the oil storage tanks with 280 250kg bombs, all the aircraft release their bombs, and all the bombs hit inside the area of the tank farms, and the wall of the tanks consisted of one inch thick mild rolled steel, a computer simulation was run that distributed the 280 bombs randomly within the target area. Over 1,000 trials, in 90% of the cases between 22 and 35 tanks were hit directly and another three tanks breeched by blast or bomb fragments. This represents 46% to
69% of the fuel tanks, or 259,000–389,000 metric tons of fuel.
Each of the fuel tanks was surrounded by a berm (called a “tank dike”) high enough to contain the entire capacity of the tank, plus extra volume to account for sloshing created by oil pouring rapidly out of a wall rupture. The radiant heat from a fire inside one tank dike can eventually ignite oil in neighboring tanks or dikes, but it would take at least an hour. The tank farms had a system of water piping and stray monitors to cool the surrounding areas to prevent the spread of the fire. Every tank would also have a built-in firefighting foam system. Since the Pearl Harbor tanks were relatively new, they likely had a central bunker that controlled the firefighting measures. Fuel from a burning tank or dike area could also simply be pumped from a burning tank into a safe tank. Transfer pumps were installed outside the diked area for this purpose.
There was a 10–15 knot breeze blowing at the time of the attack, so any smoke from upwind tank fires could conceal intact tanks, making the bombing problem more difficult.
The model suggests that about half the oil storage tanks would be destroyed. This is probably a high estimate. Setting fuel tanks on fire is a lot more difficult than it would seem. For example, the Haifa refinery and tank farm was shelled by Italian cruisers during World War II, without starting any fires. During the first Gulf War this refinery was the target of about a dozen Scud missiles. There were no direct hits, but one that exploded in a shopping mall across the street showered the refinery with hot missile parts, some of which hit and penetrated tank roofs. None started a fire.
It is hard to estimate the immediate effect of this loss on Pacific Fleet operations. Fuel certainly limited operations west of Hawaii, but this was because of limited fuel transportation and forward area storage, not a lack of the commodity itself. The main problem with far Pacific operations was a lack of tankers bringing fuel forward from Pearl Harbor, and fast tankers equipped for underway replenishment of the far-ranging carrier task forces.
A real measure of the impact of the destruction of the tanks and fuel would be how long it would have taken to restore the damage.
Oil tanks are simple constructs—a steel shell, a floating top, and a roof. The shell was essentially shaped sheet metal, something easily handled by the shipyard. It would have taken about 5,000 tons of steel to reconstruct the damaged or destroyed tanks. That amount of metal could have been provided by one cargo shipment from the West Coast. The consequences might have been on the order of imposing a two-month delay in the construction of two destroyers.
Replacing the fuel stockpile would require allocating sufficient tankers to provide the cargo lift needed. The table shows the number of tankers that would have to be assigned to the West Coast–Pearl Harbor run to replace the lost stockpile in the stated time.
At the end of 1941 there were about 120 tankers under US registry, with another 80 in Allied service under Panamanian registry and other flags of convenience. Ships were there—it was a matter of which tasks had the highest priority.
On December 8th, 1941, tankers could have been diverted to the Pacific without disrupting the war effort. Over the following January, February, and March, 43 tankers were sunk along the American eastern seaboard, the Caribbean, and in the Gulf of Mexico by U-boats.75 Many of these ships were engaged in the US domestic trade delivering oil and gasoline to cities in the northeast. Even with the loss of these ships to the Germans’ Operation Drumbeat, and dozens more in the following months, the American European war effort in 1942 was not hampered by fuel shortages. This indicates that some fraction of these 43 lost tankers could have been diverted to the Pacific in December 1941 without affecting the course of the war.
Sending tankers to the Pacific when Admiral King had yet to establish adequate ASW defenses along the Atlantic seaboard would likely have preserved them from the Germans. The Japanese were never effective in interdicting sea lines of communications, even in the opening days of the war when they deployed more than a score of their best submarines to surround and isolate Hawaii, so the ships would have been relatively safe in the Pacific.
The Japanese could have destroyed a significant part of Pearl Harbor’s stored oil. However, the consequences of these losses would not have been as bad as represented by Kimmel and Nimitz. The idea that the fleet would have to withdraw from Pearl Harbor is nonsense. Tankers could have served as temporary storage until the surface tanks could be restored, or alternately, the construction of the underground tanks could have been accelerated. As for delaying the war for two years, that idea is hard to accept when the storage tanks could have been rebuilt and the stockpile restored in only a few months.
This analysis indicates that Kimmel’s and Nimitz’s statements were wrong. There are three reasons why their statements should be taken with the proverbial “grain of salt.”
The first is the magnitude of the mental trauma that had been inflicted on them. They had grown up in the service with the feeling of absolute superiority over the Japanese. The sight of sunken American battleships was indeed the shock that Yamamoto expected it to be. It communicated despair thousands of miles away. On 8 December 1941, in Washington, Admiral Nimitz absorbed the news of the attack:
To his old friend Captain F.E.M. (“Red”) Whiting, the Bureau of Navigation’s director of recruiting, Nimitz expressed his despair. “Red,” he said, “we have suffered a terrible defeat. I don’t know whether we can ever recover from it.”76
In other words, admirals, even brilliant admirals, can be hit by the emotion of the moment.
The other difference appears to be the context that the Admirals were considering. If the entire Pearl Harbor fuel storage was destroyed and not restored, and the United States Navy fully deprived of its mid-Pacific refueling station, then the fleet certainly would have to fall back on its fuel supply at the continental United States, and the war might very well have been extended. If things had remained with the same level of tanker resources assigned to the Pacific, the Admirals’ assessments might have been accurate.
But had the admirals considered what could have done to mitigate the problem their answers would have been different. Neither were men to accept setbacks passively. Both would have seen ways to overcome the destruction of the fuel storage tanks. The fact that such informed individuals would have considered it so significant is an indication that corrective measures would have been afforded the highest priority. Tankers would have been diverted from the East Coast and replacement storage tanks shipped to Hawaii and assembled rapidly, with little impact on the course of the war.
Lastly, there was the Red Hill Underground Fuel Storage Facility. This facility was classified “Secret.” Nimitz’s statement could have been made as “cover” for this facility. If needed, the project could have been accelerated. Indeed, while most documents indicate that the first of 20 tanks was officially placed into service in September of 1942, tour guides at the facility state that on 7 December 1941 there were three completed tanks, one full of fuel.
The idea that the destruction of the fuel tanks would have forced the Pacific Fleet out of Hawaii and extended the war by two years is a myth.
4) Blocking the Channel
Fuchida briefed the Japanese aviators to be alert for an opportunity to sink a ship in the channel to “bottle up” the fleet. During the raid Nevada got underway and was passing by the naval shipyard when the second-wave dive-bombers arrived. About 14 dive-bombers went after Nevada, while seven others went after two underway destroyers, Dale and Helm. Nevada took five hits.
Historians think this was a worthwhile effort. Willmott states, “Had [Nevada] been sunk in the channel, especially if she had been sunk in the channel between Ford Island and the gate, the ability of Pearl Harbor to function as a base would have been seriously imperiled.”77 Goldstein, Dillon and Wenger claim that “If a large ship should sink in the narrow channel, it would close the harbor for weeks, perhaps months, not only trapping any ship in the harbor but also denying entrance to those outside.�
��78 Slackman, showing how these assessments are propagated in the historical community, cites Prange when he claims that the attackers “could turn Nevada into a cork which would bottle up Pearl Harbor for weeks, perhaps months, to come.” He goes on to make the rather remarkable assertion that “Rendering [the channel] unusable, even temporarily, might well have allowed Japanese forces to drive the U.S. Navy from the Central Pacific and jeopardize American control of Hawaii.”79
The channel in 1941 was approximately 400 yards (1200 feet) wide. If a battleship with a 100-foot beam sank in the exact middle of the channel, 550 feet of clearance on each side would remain, more than enough for any ship to pass. If the ship was sunk off to the side of the channel, the remaining channel width would have been even greater.
The greatest blockage would come if a ship was at a right angle across the channel. But even if a 600-foot long ship was sunk broadside across the middle of the channel, there still would have remained 300 feet on each side for ships to pass.
The chances that a ship would sink in this way were miniscule. Ships do not sink instantly. A ship’s commander would recognize that his ship was sinking and take the ship to the shallows and beach her along one side of the channel, as was done during the attack by Nevada and Vestal. If she lost power, there were yard tugs available. When Nevada was beached off Hospital Point, it was in a controlled manner assisted by a yard tug and a minesweeper.
The solution to any channel blockage would be to dredge a channel around it. Pearl Harbor had a soft bottom of loose silt which required constant dredging. Dredging around a wreck could be done in short order. Aerial photographs taken during the attack show two dredges working the harbor, one that Nevada dodged in her sortie.
