Alan D. Zimm
Page 31
The Army had a significant anti-aircraft capability on Oahu. The Coast Artillery forces which bore primary responsibility for air defense had 26 3-inch AA in fixed positions around Pearl Harbor, 60 mobile 3-inch AA, 20 37mm and 107 .50-cal.3 Other .30 and .50-cal machine guns with ground forces units could be set up in the AA role. Of the 3-inch guns, only the fixed batteries of the seacoast regiment were in position when the first attack came. The mobile guns were miles from their designated firing positions. The joint Army-Navy exercises that had been held on Sunday mornings over preceding weeks were not scheduled on 7 Dec.4
The fixed AA positions had their own ammunition magazines at the gun positions, but they were not manned under Alert 1. The gun crews were billeted at Fort Shafter. The mobile 3-inch AA guns and support vehicles were parked at various Army stations about the island. For example, the mobile batteries that were assigned to defend Wheeler Field were parked at the adjacent Schofield Barracks. They were parked without ammunition. The 3-inch AA ammunition was located in a storage depot at Schofield Barracks and an ammunition storage bunker at Aliamanu Crater, about three miles from Ft. Shafter.5 The AA batteries were also undermanned, with many of their personnel new inductees or reservists with less than 90 days in the service. When properly emplaced the AA batteries would have been controlled by state-of-the-art directors, many with radar.
The antiaircraft detachment of Battery P, 55th Coast Artillery (CA) (155mm) came into action at 0815. They fired 89 rounds of 3-inch and were credited with two kills. HQ 2d Battalion, 97th CA (AA), opened fire with small arms at 0815. Battery F of the battalion fired 27 3-inch rounds beginning at 0900. With those bright exceptions, other than small arms and machine guns improvised as AA weapons at the airfields, Army AA was nonexistent.6
The Army Air Corps
The Army Air Corps had 64 P-40, 20 P-36, and 10 P-26 pursuit aircraft operational on Sunday, 6 December 1941, a total of 94 fighters. There were an additional 35 P-40, 19 P-36, and 4 P-26 aircraft in a maintenance status. The P-26 lacked the performance to engage the more modern Japanese aircraft. The P-40 and P-36 were capable, modern aircraft.
When in Alert 2, all available squadrons were on immediate alert, with aircraft dispersed among the 85 revetments capable of protecting 109 aircraft;7 pilots wearing their flights suits were standing by their aircraft. Air patrols were launched at 0430 each morning.
Alert 2 was in place until 28 November. General Short then instituted Alert 1, which consisted of measures to defend against sabotage. Alert 1 assumed that there was no threat “from without.” The pursuit wing was placed on 4-hour standby. Even then, pilots were restricted to the base and were available to fly on very short notice. That restriction was lifted on Saturday, 6 December 1941. All but the duty officers were given the weekend off. Ammunition was removed from the aircraft and locked in storage in accordance with peacetime procedures.
Historical Results
The Japanese lost 29 aircraft, nine out of the first wave and 20 out of the second. Of the 20 second-wave aircraft, between eight8 and eleven were shot down by defending P-40 and P-36 aircraft. There were eight P-40 and six P-36 sorties during the attack, a total of fourteen, with at least two pilots flying two sorties.9 The USAAF awarded nine official kills distributed among five different pilots.10 Two to four kills could be attributed to ground fire from AA weapons defending the airfields.
Consequently, 14 to 19 kills can be attributed to ships’ guns.
An additional 20 Japanese aircraft that managed to regain their carriers were damaged beyond repair, some pushed overboard immediately. In total, 111 recovered aircraft were damaged,11 and 55 aviators were either killed or mortally wounded.
There have been several analyses that have looked at the effectiveness of World War II anti-aircraft fire. One study calculated rounds-per-kill for ships in the Pacific Theater firing at kamikaze and non-kamikaze targets over the duration of the war.12 Another study broke down AA ammunition expenditures to “rounds per bird” (RPB), that is, rounds per aircraft shot down, on a year by year basis.13 The lowest RPB was in 1942. This was likely because early in the war ammunition was scarce and there was a tendency to hold fire until the targets were well within range and most likely to be shot down. As the war progressed AA batteries tended to open fire earlier and be more willing to expend ammunition on crossing targets and other difficult shots; plus, there were more ships and more guns firing on each target.
The table provides rounds per kill for various AA weapons.
These numbers are not precise. For one thing, rarely was there only one type of weapon firing on a target. For a torpedo bomber attacking through a barrage put up by every weapon that could bear, it would be impossible to attribute a kill to a particular weapon—“shared kills” would be the norm. The figures provide an order of magnitude estimate connecting ammunition expenditure to kills.
The CinCPAC AR lists the ammunition expended during the attack. It obviously cannot be totally accurate, since some ships (such as Arizona and Oklahoma) could not provide figures. Using the highest and lowest estimated rounds-per-kill listed above, a first-order estimate of kills can be calculated:
The Congressional Investigation was presented with different numbers for heavy AA, but included ammunition expenditure numbers for machine guns.14
The 14–19 kills actually shot down during the engagement by ships’ guns are at the low end of the range of estimates of what they ought to have accomplished, half to one-third the average performance of ships’ AA during 1942 but approximately the same order of effectiveness as the average performance over the duration of the war.15 This below-average performance has been attributed to “impromptu American gun crews, faulty ammunition, and the cramped conditions in the moorings.”16 The effects of surprise, interrupted ammunition supplies, interrupted fields of fire, and lack of 100% manning for the guns and directors contributed, with some of those effects offset by the high level of training and the skills of the long-service sailors in the fleet.
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 h
eavy 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;17 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.”18 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.19
Many of the Army’s AA batteries were manned by young reservists with less than 90 days Regular Army experience.20
The CinCPAC AR identified three periods of attack:
0755-0825 torpedo and dive-bombers (30 minutes)
0840-0915 horizontal bombers (35 minutes)
0915-0945 dive-bombers (30 minutes)
While the times are somewhat inaccurate—for example, a more accurate estimate of the second wave dive bomber attack on the fleet would give the attack lasting between 0854 to 0930—the overall duration of 95 minutes likely reflects how long AA guns were engaged fairly well.
Twenty six guns firing at a sustained rate of eight rounds per minute21 would be expected to destroy 12 to 30 aircraft. At four rounds per minute (assume targets were in range only half the time), 6 to 15 aircraft would be downed. The figures serve as an upper and lower bound for the expected number of rounds fired. The lower rate of fire does not imply that the guns were fired slower, but rather account for times when the gun was not firing due to changing targets
, or a lack of appropriate targets.
40-Minute Notice for AAC fighters
In Alert 2, which the Army maintained up until 28 November 1941, the AAC fighters were ready to fly.
The army fighters, for their part, were cocked and primed; they were the ones standing alerts in their bunkers about Wheeler Field. Ground crews virtually “lived” next to their assigned planes. Alert pilots, rotated by squadron, were dressed in flight suits and either sat in their cockpits or lounged in the under-wing shade.22
According to one pilot, “We were under virtual house arrest. It was tough to get your laundry done and get to the PX. We were in our flight suits for a week at a time and got pretty ripe.”
Sunday, 7 December, was the first Sunday for months when the alert was relaxed. Unlike Alert 2, the controls in unattended planes were locked using a large metal collar that fit over the joystick, with four cables attached to the seat. They were difficult to remove even under normal circumstances.23
The Japanese had originally scheduled their attack for one of these alert periods, but the attack was delayed. According to Araki and Kuborn:
During the week proceeding 7 December, the entire Hawaiian Department, by order of General Short, engaged in a full-scale exercise for seven consecutive days. Army units from Schofield Barracks deployed, antiaircraft units drew ammunition and set up stations all over the island, and the Hawaiian Air Force armed aircraft and dispersed them to protective revetments. The warning center was fully operational and launched aircraft against simulated attacking targets.24
There were 94 fighters operational on 7 December, lower than the norm. Many aircraft had been put out of service to catch up on maintenance deferred during the previous weeks of alert. One entire squadron was placed out of service to remove and clean their guns. Under normal circumstances, this work would probably have been done on a plane-by-plane basis during the overnight hours. Adding these aircraft into the total would give 106 available fighters.