Pearl Harbour Statistics

Having recently aquired a copy of Alan Zimm's book [1] about the Japanese attack on Pearl Harbour (PH) on the 7th of December 1941 to check what he said about the Japanese gaming in preparation for the Midway campaign, I have been browsing through the rest of the book.

Chapter 9 was one of the first sections of the book to attract my attention as much of the material in it is central to many of my interests. This chapter is primarily about what might have been the outcome if some of the circumstances of the attack had been slightly different from what did occur, in particular what might have been the outcome if PH had 40 minutes warning of the impending attack. This analysis is built on the statistics of what did occur, and it is these I want to look at.

Historical Data:
1. Japanese losses were 29 aircraft, 9 from the first wave and 20 from the second.
2. Of the second wave between 8 and 11 were downed by the 14 defending fighters that were effective in getting airbourne (8xP40's and 6xP36's), compared to the 9 official kills recognised by the USAAF.
3. Airfield AA (anti-aircraft fire of all types) accounted for between 2 and 4

Then subtracting the above kill figures from the total Japanese lossess Alan allocates between 14 and 19 kills to fleet AA fire, which he then shows is at the lower end of the number of kills that might have been expected based on statistics for the Pacific in 1942 and the Pacific War in general.

The major flaw I find with this, and the subsequent what-if analysis is that he accepts the numbers for air-to-air kills. It is well know that claimed and confirmed air-to-air kills were greatly inflated [2]. The overclaiming typically could be by factors of between 2 and 10. A concrete example of an extreme case of this is the exchange ratio between F86 Sabres and Mig15's in Korea, where the claimed exchange ratio is ~10:1 which in a Rand study of 2008 the actual exchange rate is estimated to have been more like ~1.8:1 and may have been as low ar 1.3:1 against Soviet pilots of comparable experience to the USAF pilots [3].

Applying a moderate factor of 3 correction to the claimed air-to-air victories reduces the number of Japanese lost this way to ~3. Which leaves 22-24 kills for fleet AA, which is closer to "typical" number to be expected. This may-or-may not make a substantive difference to the final result of the 40 minutes warning calculation, but in the words of LtCmdr Ericson "It's not vital, but you might as well get it right" [4] or rather try to get it right.

References
1. Zimm, A.D., Attack on Pearl Harbor, Strategy, Combat, Myths, Deceptions, Casemate, 2011
2. Wikipedia Contributors, http://en.wikipedia.org/wiki/Confirmation_and_overclaiming_of_aerial_victories_during_World_War_II, retrieved: 27 March 2014 07:50 UTC
3. Wikipedia Contributors, http://en.wikipedia.org/wiki/North_American_F-86_Sabre, retrieved: 27 March 2014 07:50 UTC
4. Monsarrat, N., The Cruel Sea, Cassell and Co, 1951.