Not sure where these numbers come from,
USN post-war analysis showed the number of 40mm rounds required to bring down a plane was in the order of thousands. Same analysis indicated the number of 5"rounds/plane in the order of hundreds.
Rather simple really. And the "thousands" is a bit disingenuous as a statement or perhaps a bit misleading, as the numbers were 1713 rounds per kill.
For the total of the war, 654 5" non VT fused were required to bring down a plane, 340 if VT fused. 1713 per round of 40mm. I'd add this that these are the stats for the entire war, and really there were two separate periods and types of attacks. The Kamikazes change the stats a bit for a few reasons. As the Japanese did not face kamikazes, my concern is how AA worked when the two sides were more evenly matched - not after Japan was in essence defeated and resorting to kamikazes.
To make it a bit more brief, my concern is how the AA type functioned against conventional attacks, not kamikazes.
But back to you question/issue, and we can use full war stats as opposed to the 42-43 I was looking at.. The 5" rounds average a kill per 497 rounds, the 40mm 1713. How indeed does a 40mm kill more birds per minute than a 5"/38?
You are probably forgetting that rate of fire is a big factor here on birds per minute. THe 40mm has a much higher ROF. 1713/120 means the 40mm has on target about 14 minutes and 16 seconds roughly per kill. The 5"/38 with an ROF of 18.5 needs to be on target 497/18.5, or almost 27 minutes.
No, I attached the excerpt from USN Technical Mission to Japan, and it says "range LESS then 2000m and altitude LESS then 1000m". ANd the figures quoted later in the body of the document are of 1000meters and 800meters.
Again, a bit of a misleading statement. What you are failing to mention is the lesser numbers have much to do with the Japanese doctrine of conserving ammunition, something the US never had to worry about. In that same excerpt, it stats that with the reduced ranges the Japanese numbers were is high as 7 rounds per bird. I think those numbers are way off, but it does indicate they here holding back fire until the most optimum range.
And really, less than 2000? less than 1000? Would you not describe a weapon with a 5000 meter AA ceiling as effective at ranges of less than 5000meters? Or I guess less than 5001 meters? Seems like we are playing a bit of semantics here. Either way, the effective range is at least 2000 meters, even if due to concerns about ammunition supply they held back their fire longer.
I'd like to point to this information of the 25mm from Navweaps, a very reliable source:
AA Ceiling @ 85 degrees Effective: 9,843 feet (3,000 m)
Maximum: 18,040 feet (5,500 m)
My point is that it's "effective range" was much greater than 1000 or 800 meters - again, is was Japanese doctrine or more importantly desire to conserve ammo that caused them to hold fire to 1000 or 800 meters. And this probably also plays into their fairly decent rounds per bird number, which came out better than I thought.
As a comparison, US .50 caliber gunners were instructed to open fire a few hundred meters outside of what was deemed their effective range. The idea being that it would be easier to walk the tracers to the target.
I read that, however the only thing I see about a 160 RPM rate of fire is this - "The 40mm gun can be operated either fully automatic or single fire. In automatic, it is capable of a maximum cyclic rate of fire of approximately 160 rounds per minute."
That is indeed true, but I see nothing where it retains the 160 ROF at elevation. Check Navweaps - it goes more in depth into the rate of fire issues.
The same article you pointed me to also says this, which is where I think you got your range factors from - "Of twelve different types of 40mm ammunition which were produced, five types were in use at the end of the war: high explosive incendiary bright tracer, high explosive incendiary dark tracer, night explosive incendiary dark ignition bright tracer, armor piercing, and high explosive incendiary bright tracer non-self-destroying ammunition. The muzzle velocity of the projectile averages 2390 feet per second and the tracer burning time varies from 8.5 to 10.5 seconds depending; upon the ammunition type. This burning time gives an approximate range of 4200 to 4500 yards."
Note this is a discussion on the types of ammo available for the 40mm. It is stating how long the tracer burns for and how many yards out it burns - which is certainly not the equivalent of the effective range of the weapon. I had mentioned that some rounds self destruct at this range to avoid friendly fire issues. Again, this is not the same as effective range of the weapon.
I'll say this again, "effective range" is a very gray area, what one source deems "effective range" may be different than what another source thinks of "effective range". Which is why I like to look at things like AA ceilings, not that the guns are effective to their maximum ceilings, but it provides a good comparison as to the ranges of the weapons.
Francis Marliere wrote:
Estimating the effectiveness of flak was difficult. Naval officers could and did have sometimes very different opinions on guns and gunnery. I am away of my sources and can't find the name of this USN guy fighting in the Solomos late 42 (my be captain Gatch but not sure) who thought that 5" guns were useless and should be replaced by light flak. Admiral Halsey did not approve and replied that
- 5'' guns were effective and did shoot down planes
- 5" guns were fine because they could protect a fleet while light flak could protect only a ship
- the main duty of flak is not to shoot down planes (it's fine but secondary), but to make planes miss their target. 5'' guns deter air attacks as well or better than light flak
I fully agree here, which is why it's very tough to compare "heavy flak" to light flak. Light flak can really only defend the ship it's on or a very nearby ship depending upon formation and other issues. With a 5" gun on the other hand you can protect the entire task force, or at least a good portion of it depending upon task force size. And the problem with much lite flak as that it can often be a revenge weapon, shooting down the plane after it has launched it's ordinance.
For a pound of weight on top vs air plane shot down, light flak wins, but it does not protect the fleet. Nor does it do as well what secondary armaments were initially designed to do, protect against smaller surface vessels from torpedo range.
Anyway Alecsandros, I just said that one should not trust too much the rounds per bird statistics. There is no doubt that US flak was far more effective than Japanese one.
Never doubted that one little bit, as a matter of fact it is what I stated when started this thread. How anyone would think that I'm saying Japanese AA was as good or better than US AA in WW2 is beyond me, perhaps some nationalistic tendencies? I really don't know. It appears some look at it as heretical if I say anything remotely positive about Japanese AA when doing a detailed cerebral comparison.
My only point was that the Japanese 25mm which is often much maligned was not a bad weapon. It's roughly equivalent, perhaps even a tad better than the US 1.1" AA weapon. Now, the US replaced their 1.1" with the Bofors as fast as they could, but the 1.1" was not a bad AA weapon, it's just that the Bofors was a fair amount better. I'd guess that the Bofors was maybe 2-3 as effective as a 1.1" or 25mm, and about twice as effective as the 40mm "pom-pom" against conventional air attacks per barrel (this last part per british evaluation of their own weapons). Of course, there was a price to pay, the 40mm weighed in more per mount, barrel and ammo than the other weapons did. The Japanese 25mm was superior to the 20mm Oerlikon to some degree, and was similar in topside weight. The Oerlikon did have about 2.5x the effective rate of fire, but the 25mm had about double the range, and a heavier projectile.