Attack on Pearl Harbor (39 page)

40 Minutes Notice for the Fleet

If the fleet had received 40 minutes of warning of the air attack, General Quarters (GQ) would have been set throughout the fleet. The usual time to set GQ at sea was eight to ten minutes; in port on a Sunday, the factors of “surprise,” “peacetime,” “men ashore,” and “hangover” would cause delays, but not over 20 minutes. Battle stations would be manned, including AA gunnery for defense, engineering for reliable ship’s electrical power, high and low pressure air for the guns, and firefighting water pressure. Damage control stations would be ready to fight fires, de-water spaces, control flooding, and counterflood if necessary.

On that Sunday morning 65% of the officers and 95% of the crew were on board, so battle stations would be sufficiently manned, the most serious potential deficiency being officer leadership in the AA gun directors. With 40 minutes of warning, all the AA gun directors would have been manned. This is significant, because the US Navy was the world’s leader in accurate AA gun directors, which would be aiming the acknowledged world’s best heavy naval AA gun, the 5”/38. The fleet had been training hard over the previous year, so the personnel were at a high state of readiness, with many cross-trained to fill different roles at their battle stations.

Material condition Zed would be set. This would put the ships in their maximum state of watertight integrity. In those ships that had inspection covers removed from their torpedo defense voids the engineers would get a start on replacing the covers, but there might not be time to get them all, unless local Damage Control parties doing their pre-battle tour of their spaces were clever enough to recognize the problem and pitch in.

Magazines and ready service lockers would be unlocked and ammunition passers on station to ensure an uninterrupted supply of ammunition. There would be some time to clear away objects interfering with the AA guns’ fields of fire. Nests of destroyers might be able to separate, providing their guns with clear fields of fire.

Fire would be opened with the heavy AA guns as soon as the first wave Japanese formations were sighted, at 0750 or earlier, compared to 0805 as reported in many of the ARs. There would be an additional approximately 15 minutes of fire from all available AA guns, with a better supply of ammunition to the guns for the duration of the attack.

There are various counts of the number of heavy AA weapon. One records 353 3-inch and 5-inch AA guns on the ships in Pearl Harbor;
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another gives the numbers as follows:

Some of these weapons were broken down for maintenance, and many could not be brought to bear due to blocked fields of fire. The number able to engage can be estimated by examining the locations of the ships and their material readiness condition. For nested battleships, only 50% of the heavy batteries could engage (the outboard guns), and for nested destroyers, it was assumed that only eight 5-inch guns would come into operation per nest (the superstructure of adjoining ships would limit the arc of fire of some guns). For ships pierside at the Navy Yard with ammunition and functioning guns, only half their available guns were assumed to come into operation.

Rates of fire for the 5”/38 and 5”/25 is largely a function of crew skill, and can be anywhere from 10 to 20 rounds per minute (rpm) when on target. Later in the war, trained 5”/38 AA crews recorded 22 rpm over short durations of fire, and 15–17 rpm over a sustained 30-minute trial.

The average rate of fire was set at eight rpm, assuming that 50% of the time the guns would not have a target. This figure is taken from the average rate of fire of the 5”/38 guns aboard
North Carolina
(BB-55) during an air raid on 24 August 1942 in an environment that was similarly “target-rich.” Over 10 minutes
North Carolina
fired at approximately 49 dive and torpedo bombers and 12 high-altitude bombers.

Similar assumptions were made for the 3-inch, 1.1-inch, and machine gun batteries. The automatic gun batteries were considered to fire only for ten minutes due to their shorter range.

Using rounds per kill figures consistent with the actual results during the attack allows a calculation of the estimated kills during this first 15-minute period.

Potentially, about 32 kills could have been achieved in the period 0750 to 0805, before the ships historically opened fire against the first wave.

Adding the five first wave kills attributable to ship’s guns actually destroyed from 0805 to the end of the first wave and the total first wave losses over the fleet would then be approximately 37 aircraft. However, with warning the number of kills after 0805 would have been greater than achieved historically. In the battle there were interruptions in the continuity of fire while magazines were opened and the ammunition train established. For example,
California’s
commanding officer reported, “The shortage of ammunition immediately available at the guns was acute, and orders were issued to ammunition parties to expedite the service of it to the guns.”
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In the actual battle most of the guns had only two to three minutes worth of ammunition in their ready service lockers. For example, the battleships’ 5”/25 gun ready service lockers held 15 rounds, or a little under two minute of fire at the assumed rate of eight rpm. If it took eight minutes to set GQ, the guns had a potential shortfall of six minutes’ firing. With GQ set all of the guns would have been manned rather than just the “ready” guns. The guns would likely have expended four times the ammunition. These assumptions lead to an estimate of 20 kills from 0805 to 0813, 15 more than actually occurred, which can be added to the kills calculated for the period 0750 to 0805.

With a better AA defense there would be fewer torpedo and bomb hits, and more of the ships’ AA guns would have remained in action longer—for example,
Oklahoma
with material condition Zed set and damage control parties on station would likely not have capsized as quickly, if at all, adding her 5”/25 heavy AA and .50-caliber machine guns in the fight. So, the number of historical kills used as the starting point of the calculation—five kills—would likely have been larger.

The calculations indicate that the Japanese could have lost many more aircraft than they did. This is not particularly surprising—if anything, the estimate might be low, considering the number of guns that could be brought into action at Pearl Harbor compared to the volume of fire generated by the carrier task forces at Coral Sea and Midway and later carrier battles, where some attacks lost over 50% and sometimes over 75% of their aircraft.

The additional kills would likely be concentrated amongst the torpedo bombers. With warning, the calculations indicate that 20 to 34 torpedo bombers might be shot down, many before they could launch their torpedoes, leaving perhaps 20 to 28 torpedoes in the attack. Considering that five of the last seven torpedo bombers to attack were shot down when the full volume of defensive fire was developed, it is likely that more would have been shot down had the fleet been alerted.

The storm of fire opposing the torpedo bombers would have disrupted the delicate task of establishing the critical flight conditions for a successful drop. If the numbers from the British study of bombing in the Mediterranean apply, the hit percentage could be reduced by 60% from what could be achieved against undefended ships. Applying this reduction to the hit percentage actually accomplished in the raid results in a hit percentage of 19%. This is still greater than the average of 15% hits achieved by torpedo bombers throughout the war. If the fleet had 40 minutes of warning it is possible to justify only five total torpedo hits, perhaps four against battleships. Four hits could have sunk one battleship or damaged four.

In this scenario the second wave would have encountered more fire than the first wave due to fewer ship losses. A conservative estimate would be to credit the ships with the lower range of kills as occurred historically. The higher estimate would be the higher range of this kills that happened historically, with additional kills credited to the guns of Battleship Row.

Kills against the first wave were calculated to be significantly higher than those against the second wave. This can be attributed to several causes: first, the torpedo bombers were more vulnerable targets, and would have been engaged by at least twice as many machine guns than in the historical case, with a full volume of fire greeting the very first aircraft; second, the first wave attack was strung out, with aircraft coming in to attack almost one at a time, providing more sequential firing opportunities for the defenders.

40 Minutes Notice for the Army’s 3-inch AA Batteries

With 40 minutes notice the Army AA batteries could have had time to man the 26 fixed 3-inch AA guns in emplacements around Pearl Harbor. The gun crews were quartered at Fort Shafter. There were ammunition magazines at each site.

In 1946 the General Headquarters, US Army Pacific issued a report, “Anti-aircraft Artillery Activities in the Pacific,” which included rounds expended per kill figures for 90mm, 40mm, and .50-cal weapons. It credits the 90mm AA gun with about 400 RPK, the same order of magnitude as the 1942 Navy 5”/38 figures. The Army report had its data from official reports or accredited sources, and the numbers of kills cited are claimed to be conservative.
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