WesWorld

Quoted

Originally posted by Red Admiral
Statisically the US 3"/50 is a better weapon than the 5"/38 mostly from it's higher muzzle velocity which gives greater accuracy. The extra shell size doesn't make much difference as you pretty much need a direct hit to shoot something down, the lethal radius (even if fused properly) isn't particularly large for these shells. A shell with a contact fuse fired at high velocity is the best solution to actually shoot something down. Thats where the 65/64 comes in, with very high velocity and a shell large enough to kill the largest aircraft with a single hit but all in a smaller lightweight weapon system. The automatic version is still some years off, but semi-auto with 20-25rpm is very doable.

Theres not a lot of difference between 37mm and 40mm weapons, both need 2 or 3 hits to bring something down.

Italian fire control systems for AA were two types, Galileo system which was similar to HACS and the later San Giorgio which was tachymetric.

Quoted

Originally posted by Red Admiral
The 3" shell has a burst radius of around 8m so you pretty much need a hit to bring down an aircraft. Statisically the 5"/38 isn't as good, requiring 960 rounds per plane against 752 for the 3". (Numbers here) The only real thing that can account for it is that the higher mv of the 3" round which makes the fire control solution easier - or the sample isn't statisically significant. The rates of fire for the 5"/38 seem to have been overstated, with around 12rpm being the normal rate from data in the after action reports.

Quoted

Editor's Notes

by Tony DiGiulian

The following tables adapted from information given in "Naval Weapons of World War Two" by John Campbell show the USN's anti-aircraft successes between October 1944 and January 1945:

Kamikaze Actions
.
Weapon
Planes Shot Down

Number of rounds per plane

5"/38 using AA Common
19

1,162
5"/38 using VT
24.5

310
3"/50 using AA Common
6.5

710
40 mm Bofors
114

2,272
1.1" MG
1

2,231
20 mm Oerlikon
62.5

8,972
0.5" MG
2.5

28,069

Generally speaking, Kamikaze actions were at very close range with the aircraft closing fast upon their intended target. These sort of engagements were very difficult for weapons firing time-fuzed ammunition, as the rate of change in the ballistic range to the aircraft also meant that the fuze settings needed to have large changes from one round to the next. Any lag or delay in getting a particular round into the air after its fuze had been set meant that its detonation would be too far away to reach the target aircraft. The VT fuze eliminated that problem, as noted by its far smaller rounds per aircraft rate.



Non-Kamikaze Actions
.
Weapon
Planes Shot Down

Number of rounds per plane

5"/38 using AA Common
33.5

960
5"/38 using VT
20

624
3"/50 using AA Common
4

752
40 mm Bofors
46

3,361
1.1" MG
0

(4,764 total)
20 mm Oerlikon
50.5

7,152
0.5" MG
3

15,139

In this table the advantage of the VT fuze, while still significant, is not nearly so pronounced as in the previous table. This may be due to the fact that the rate of change of the attacking aircraft's ballistic range did not change as rapidly as did a Kamikaze aircraft, thus allowing the fire control computers more time to process the incoming data and produce better time fuze settings. It is interesting to study the success rate of the 3"/50 gun, as this weapon was adapted post-war with automatic loading and VT fuzes to replace the 40 mm Bofors on most US warships. Even without VT fuzes, the shoot-down rate of the smaller weapon compares favorably to that of the 5"/38 firing VT-fuzed ordnance. Although, the high numbers for the 5"/38 may be a result of the fast firing rates of these weapons and the fact that nearly every warship destroyer-size and larger carried several of these weapons. So, even a pair of destroyers could fire over 200 rounds per minute.

For more information on the VT fuze, see the Ralph Baldwin book, "The Deadly Fuze - Secret Weapon of World War II." An analysis in this book of the 278 aircraft shot down by VT fuzed projectiles between October 1944 and August 1945 indicates that only 46 of these would have been destroyed if time fuzed projectiles had been employed. However, Will Jurens, noted ordnance authority, estimates that Baldwin's 6:1 ratio apparently assumes that 70% of the VT fuzes worked. A 50% failure rate - the Navy's lower limit of acceptability - meant the effectiveness ratio was closer to 4:1. In comparison, mechanical time fuzes such as the Mk 18 typically worked about 90%-95% of the time.

Addendum
Updated 04 November 2005

Editor's Note: Some time after the above essay was written, I exchanged a few messages with a gentleman who is the Chief Scientist of the Center for Naval Analyses. In the interests of clarity and completeness, I have combined and paraphrased his comments to make the following addendum.



These data in Campbell's "Naval Weapons of World War Two" appear to be taken (and stripped of context) from some earlier work by the Operations Research Group (ORG) relating to the Philippines campaign. Speaking as the Chief Scientist of the Center for Naval Analyses, the direct descendant of ORG, I will tell you that I believe that the figures below represent a sounder methodology applied to a better data set. That said, however, I would not bet the farm on any of these numbers.

There are a lot of pitfalls in this sort of analysis, and it is extremely difficult to arrive at meaningful numbers. With this caveat firmly in mind, I will quote some of the better figures for World War II:


Type of Attack
Planes Shot Down

Rounds per Plane

20 mm

40 mm

5"/38 MT*

5"/38 VT

Kamikaze
24

27,200

6,000

1,000

200
Non-Kamikaze
41

30,100

4,500

1,000

550

* MT = Mechanical Timer (i.e., Time Fuzed AA Common)

These figures are from the Special Defense Operations Research Group (SpecORG) study, "AA Defense of the Fast Carrier Task Force - 24 October 1944 To 21 March 1945", Anti-Aircraft Study No. 8, revised 11 September 1945. They address only carrier task groups, for which the best data were available.

Another SpecORG study, AA Study 13 of 12 October 1945, "Anti-Aircraft Actions in the Okinawa Campaign, 18 March - 15 August 1945", estimated that on average the Japanese lost 3 to 10 times as many aircraft per ship damaged or destroyed in non-suicide attacks as were required in suicide attacks.

William D. O'Neil
Chief Scientist of the Center for Naval Analyses