Attack on Pearl Harbor (38 page)

Utah
in the process of capsizing after two torpedo hits. Toland’s assertion that
Utah
was attacked because she “looked like a carrier” is clearly wrong. Japanese aviators stated that
Utah
was mistaken for an operational battleship.
Source: Naval Archives, Washington DC

Initial Conditions

The US Army was responsible for the defense of the Pearl Harbor area, and Oahu in general. On 7 December the Army air defenses were in a complete stand-down, totally unready. This contrasted with the previous weeks, where the defenses were at high alert, with pilots standing by their aircraft, fighter patrols aloft at daybreak, and AA guns in position with live ammunition.

As early as 14 June 1940 the Army was practicing alerts for the defense of the islands. Lieutenant General Herron wrote of it in a letter to the Army Chief of Staff, General Marshall:

In the months before the attack the Army had constructed an aircraft warning service system patterned after that used by the British during the Battle of Britain. The full system consisting of radar and human observers connected to an Aircraft Information Center (AIC), which would control the pursuit squadrons and air defenses. The AIC was successfully tested on 27 September 1941, more than two months before the raid. In that exercise, carrier aircraft playing the part of an enemy raiding force were detected 84 miles from Oahu, giving the defenders 40 minutes to react before the attacking planes went “feet dry,” and another 10 minutes before they reached Pearl Harbor. Within six minutes Army pursuit aircraft were aloft. The raid was intercepted 30 miles offshore.
²

This was not a fully realistic test. It was scripted and the participants alert and ready to fly at the beginning of the exercise. There were still deficiencies, such as the fact that the system lacked the ability to differentiate hostile from friendly tracks. But it was a system fully capable of detecting a major carrier-launched strike with enough warning to allow the defenders to be manned and ready to receive it.

With the excuse that they lacked officers to man the center, Lt. General Short and Admiral Kimmel decided to wait until after the war began to place the AIC in operation.

On 7 December one of the system’s radars (operating beyond its scheduled time, for training) picked up the Japanese strike 136 miles north of Oahu. Before that, it had tracked the two Japanese reconnaissance floatplanes. Had the AIC been operational, the fleet and army forces would have had approximately 50 minutes warning. Additional sighting reports were called in by a ground observer and an aircraft, but the AIC was not in operation and had no authority to act on the information, so nothing happened.

However, what if the defenders had been alert and ready?

The Fleet

The fleet was in Condition Three. For the battleships, this specified that one-fourth of the heavy AA guns would be manned with 15 rounds of ready service ammunition on station per gun, along with two .50-caliber machine guns with 300 rounds each. The ready service ammunition was generally padlocked in ready service boxes in the immediate vicinity of each gun, with the keys under the control of the duty gunnery officer.

With a trained crew, the 5”/25 could fire up to 20 rounds per minute, so they had ready ammunition for about a minute’s fire. The ready service ammunition was to be immediately supplemented by the regular ammunition supply from the main magazines. These magazines were also locked, usually with the keys in the custody of the commanding officer, the gunnery officer, or the senior duty officer. In most cases the crews did not wait but broke the locks. The ready service ammunition was fired, and then there were delays and interruptions in the ammunition supply until General Quarters was set.

Saturday offered shore leave for the officers and liberty for the sailors. With few accommodations available ashore and with personal budgets more attuned to provide drinking money than overnight room rental, most enlisted men returned to their ships after liberty, and were available Sunday morning—some with hangovers, but available. Over-night absences were mostly taken by the more senior officers and senior enlisted men, some of whom were married and had establishments ashore. Some ships had as many as 50% of their officers absent on Sunday morning. The most significant manpower gap would be in manning the gun directors, where junior officers and senior petty officers were often assigned to the AA battery directors.

The Army

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 eight
⁸
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.