Japanese vs US AA capabilities

Guns, torpedoes, mines, bombs, missiles, ammunition, fire control, radars, and electronic warfare.
alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Japanese vs US AA capabilities

Post by alecsandros »

Garyt wrote: The 25mm certainly had it's shortcomings, and I'm not going to say it was on par with the 40mm Bofors. But it was not a bad weapon, and with a few changes (loading method, power mounts for all with sufficient traverse elevation spedd, sighting) it could have been an excellent weapon. I'd put it a step ahead of the US 1.1". Possibly better or on even terms with the 20mm Oerlikon, but it's tough to compare as the Oerlikon falls in the camp of smaller short range light AA, the 25mm is more mid range light AA. It's max AA ceiling of 5500 meters puts in more in line with the 1.1" and 40mm than the 20mm with it's 3050 max AA ceiling.
... Japanese doctrine up to 1944 considered 25mm AA guns effective up to 1500m range. Japanese doctrine post-1944 considered them effective out to 900meters range, but this was at least in part due to the need to conserve ammo.

1500m and 900m is not enough to protect against torpedo bombers, and certainly not enough to put in place a defensive umbrella over the fleet.

That is why the 40mm Bofors and 2-pdr British guns were so effective: they could effectively engage enemy planes out to 4000 meters, giving time to shoot down potential enemys and also giving the possibility of several ships to offer each other a defensive umbrella.

The 25-mm gun was only a short range defensive weapon, marginally better in stoping power than the 20mm Oerlikon, but less effective then the Oerlikon overall, because of the much slower output/minute.
Francis Marliere
Senior Member
Posts: 276
Joined: Mon Oct 18, 2010 3:55 pm

Re: Japanese vs US AA capabilities

Post by Francis Marliere »

Gentlemen,

a few points from Norman Friedman's lateste book on AA guns and gunnery in WWII, for what it is worth.

Statistics such as the average rounds needed to shoot down a plane can be measleading. Tactical situation is often the most important factor : a ship which is taken by surprise and cannot engage will not shoot down any plane, whatever the number of guns available. The late war USN flak, which proved very effective against conventionnal air attacks, was far less efficient against Japanese new tactics : either saturation attacks (ships did not have enough directors to engage all the attackers) or surprise attacks (directors did not have enough time to elaborate a solution).

Fire control really matters, even for light AA. From memory, remote control (getting the pointer away from muzzle blast and flash) could double the hit rate, and using an effective director (such as the Mk 14) could also double the hit rate. In relation to what I said above, the speed of director was important also. From what I understand, Mk37 with FCR was efficient but a bit slow to work.

Targets were also an important parameters. Large and slow targets were, as you imagine, easier to hit than fast and small planes. All the planes could not absorb the same amount of damage. Armor, self sealing tanks, general robustness were important. Tactics in use were also primordial : Japanse torpedo planes usually pressed their attacks to get more hits, while German and Italian ones launched their torpedoes far away, to minimize the looses from flak.

Last, from 1943, Japanese ships suffered from an acute lack of ammunition. They were allowed to fire only a few shells (can't renember the excat value) at a target, and that did not help.

If you have an interest in AA guns and gunnery, I suggest you read Friedman's book. It's not perfect, but there are many interesting things to learn.

Hope it helps,

Francis Marliere
Garyt
Senior Member
Posts: 274
Joined: Tue Dec 09, 2014 9:31 pm

Re: Japanese vs US AA capabilities

Post by Garyt »

... Japanese doctrine up to 1944 considered 25mm AA guns effective up to 1500m range. Japanese doctrine post-1944 considered them effective out to 900meters range, but this was at least in part due to the need to conserve ammo.
Yeah, effective vs. maximum range are of course two different things. The shorter range was clearly a response to a lack of ammo though.

The 1946 US technical mission to Japan found the Japanese believed the ideal range was about 1000 meters high and 2000 meters out, which indicate a range of slightly over 2200 meters however. Beyond this they believed fire was ineffective though.

I think the doctrine of Japan vs the US though had something to do with the rounds per bird of the 25mm. I think the US was a lot more free firing with their ammunition, which makes the rounds per bird go up on US weapons. Being more conservative with their ammo, the Japanese weapon would have a lower round per bird than an identical US weapon, which does not indicate the Japanese weapon was superior but that the tactical doctrine was different.
If you have an interest in AA guns and gunnery, I suggest you read Friedman's book. It's not perfect, but there are many interesting things to learn.
Thanks Francis, I will try to take a look at it.
Garyt
Senior Member
Posts: 274
Joined: Tue Dec 09, 2014 9:31 pm

Re: Japanese vs US AA capabilities

Post by Garyt »

Statistics such as the average rounds needed to shoot down a plane can be measleading. Tactical situation is often the most important factor : a ship which is taken by surprise and cannot engage will not shoot down any plane, whatever the number of guns available.
My question here Francis - if you are looking at total rounds fired per gun for a full year or even 5 years, should the tactical situations for all weapons even out with the sample base being used? I.E. shold not as many 40mm guns been surprised for instance as 20mm guns?
The late war USN flak, which proved very effective against conventionnal air attacks, was far less efficient against Japanese new tactics
That's why I left 44 and 45 out of the equation, more unconventional attacks occurred as the war went on.

It's not a fair comparison to compare US 40mm performance against kamikazes vs. Japanese 25mm performance vs. conventional attacks.

Although to take this a step further - were not results already a bit biased against Japanese AA guns as the US planes were much more durable against AA fire due to their armor and self sealing fuel tanks?
Francis Marliere
Senior Member
Posts: 276
Joined: Mon Oct 18, 2010 3:55 pm

Re: Japanese vs US AA capabilities

Post by Francis Marliere »

Garyt wrote:My question here Francis - if you are looking at total rounds fired per gun for a full year or even 5 years, should the tactical situations for all weapons even out with the sample base being used? I.E. shold not as many 40mm guns been surprised for instance as 20mm guns?
Yes and no. If a ship is surprised and can fire only for 10 seconds, light flak will fire a few shots while heavy flak won't.
Garyt wrote:It's not a fair comparison to compare US 40mm performance against kamikazes vs. Japanese 25mm performance vs. conventional attacks.
Yes. My point is that comparisons are difficult and can be misleading. I would add that I don't trust stats too much. You can learn after the war that flak destroyed x planes an a attack, but I don't know how you can determine that this plane was shot down by a Bofors or a oerlikon. IMHO, you can't trust the gunners (always the claims vs real numbers of planes shot down).
Garyt wrote:Although to take this a step further - were not results already a bit biased against Japanese AA guns as the US planes were much more durable against AA fire due to their armor and self sealing fuel tanks?
Yes, of course.

Best,

Francis
alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Japanese vs US AA capabilities

Post by alecsandros »

Francis Marliere wrote:
Yes. My point is that comparisons are difficult and can be misleading. I would add that I don't trust stats too much. You can learn after the war that flak destroyed x planes an a attack, but I don't know how you can determine that this plane was shot down by a Bofors or a oerlikon. IMHO, you can't trust the gunners (always the claims vs real numbers of planes shot down).
... Still the general idea is that putting a wall of AA death at 4,5km from own ship, using 80 x 40mm Bofors outputing 9000 rounds/minute (8100kg of ammo per minute) is more effective against any type of conventional attack aircraft than using 80 x 25mm AA guns, outputing 9000 rounds/minute (1800kg of ammo per minute) at 1,5 - 2km distance. Even doubling the number of 25mm AA guns, up to 160 x 25mm and 18000 rounds/minute does not offer the same amount of ammo output in terms of weight/minute.

SO, in the spirit of the thread, USN vs IJN AA capabilities are pretty much in favor of the former...
Garyt
Senior Member
Posts: 274
Joined: Tue Dec 09, 2014 9:31 pm

Re: Japanese vs US AA capabilities

Post by Garyt »

SO, in the spirit of the thread, USN vs IJN AA capabilities are pretty much in favor of the former...
Definitely. I never said that was not the case. My point was that the Japanese 25mm was not as bad of a weapon as it seems to get credit for. It's no Bofers, but that was the most effective light weapon of the war.

minute does not offer the same amount of ammo output in terms of weight/minute.
Throw weight per minute is not a good way to judge AA fire. Or for that matter effectiveness of any type of fire. It does have some bearing, but it's certainly not valid as a comparison factor. For instance, A bofors will put up 66 pounds per minute. A 5"/38 will do that with one round almost, and with a rate of fire of about 20 per minute per you throw weight stats it would be 17 times as effective as a bofors.
Still the general idea is that putting a wall of AA death at 4,5km from own ship, using 80 x 40mm Bofors outputing 9000 rounds/minute (8100kg of ammo per minute) is more effective against any type of conventional attack aircraft than using 80 x 25mm AA guns, outputing 9000 rounds/minute (1800kg of ammo per minute) at 1,5 - 2km distance.

These numbers are not right either as a direct comparison. Youare giving the 25mm an effective range of 32% of it's AA ceiling - yet you have the bofors effective range at 63% of it's AA ceiling. The Bofors had a better effective range than the 25mm, but not nearly by the margin you stste. The US 40mm self destructed at this range - not a fuse to hit planes with, but to self destruct to not risk friendly fire casualties. THis 4.5 km is well outside of it's "effective" range.
Yes and no. If a ship is surprised and can fire only for 10 seconds, light flak will fire a few shots while heavy flak won't.
Indeed, which is why I left out 44 and 45 as this took into account more "suprise" type attacks by kamikazes getting inside the 5" range before detected. Although this would not seem to influence the stats of the various types of light flak on a comparison basis.
alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Japanese vs US AA capabilities

Post by alecsandros »

Garyt wrote: For instance, A bofors will put up 66 pounds per minute. A 5"/38 will do that with one round almost, and with a rate of fire of about 20 per minute per you throw weight stats it would be 17 times as effective as a bofors.
... The Bofors will put up 120 rounds/minute on average (but could go as high as 160), with 2 pounds/round = 240 pounds/minute.
... The 5/38 will put up 15 rounds/minute (but could go at 20), with 55 pounds/round = 825 pounds/minute

Of course the 5/38 is more effective, especialy as it was radar guided and was equipped with proximity fuze, while the Bofors 40mm wasn't. However, the volume and weight of the 5/38 was so much larger than the 40mm Bofors that the Bofors still wins in terms of practicality. [the weigth of a quad Bofors with no subsystems was around 11tons , vs some 15 tons for the single, non-turreted, most simple 5/38]

These numbers are not right either as a direct comparison. Youare giving the 25mm an effective range of 32% of it's AA ceiling - yet you have the bofors effective range at 63% of it's AA ceiling. The Bofors had a better effective range than the 25mm, but not nearly by the margin you stste. The US 40mm self destructed at this range - not a fuse to hit planes with, but to self destruct to not risk friendly fire casualties. THis 4.5 km is well outside of it's "effective" range.
NO,
I am not giving them anything. The Japanese considered the 25mm fit for 1200m range, and the USN considered the 40mm Bofors fit for 5000yards firing.

That was mostly because the larger round tends to keep a more stable trajectory at longer range.
[this is also the case for the German Flak 20mm. It's maximum ballistic range was about 4400meters, but the effective range was no more than 1000m. A small shell simply doesn't behave so well as a larger shell in longer flights...]
Garyt
Senior Member
Posts: 274
Joined: Tue Dec 09, 2014 9:31 pm

Re: Japanese vs US AA capabilities

Post by Garyt »

... The Bofors will put up 120 rounds/minute on average (but could go as high as 160), with 2 pounds/round = 240 pounds/minute.
... The 5/38 will put up 15 rounds/minute (but could go at 20), with 55 pounds/round = 825 pounds/minute
LOL, forgot to convert my 40mm from KG to pounds. Your numbers are correct here, though. But is far as the 5"38 goes, if we pick the midrange of the expected rate of fire we are looking at 18.5x55=1017.5 pounds a minute, 4x + as effective as the Bofors.

And a 40mm has about a 7% chance of killing a bird per minute of fire - a 5" (averaging both VT and non VT as not all were VT equipped) has about a 3.7% chance.

So even though the 5" puts 4x + times the poundage in the air, the 40mm is twice as effective. And this has no bearing on the weight required to have a gun mounted - this is a comparsion of the effectiveness of a barrel of 40mm fire vs a barrel of 5"/38 fire.
especialy as it was radar guided
I'm not sure what you mean here by "radar guided" 5" shells.
I am not giving them anything. The Japanese considered the 25mm fit for 1200m range, and the USN considered the 40mm Bofors fit for 5000yards firing.
A lot of this here is doctrine for the Japanese gun, a doctrine designed to conserve ammo. I'm not sure where the 1200m range comes from either. From the 1946 US technical mission to Japan:
In interviews conducted by the U.S. Naval Technical Mission to Japan after the end of the war, Japanese military personnel cited it as the most reliable Japanese anti-aircraft weapon, but second in effectiveness to the Type 98 100 mm anti-aircraft gun.[3] The Type 96 was most effective when used at ranges of 1,000 meters or less. Japanese military estimated that it required an average of 1,500 rounds to down an aircraft at a height of 1,000 meters and a range of 2,000 meters and that fire beyond that range was completely ineffective. Later in the war when ammunition supply was restricted, firing was held until the targets were within 800 meters range this dropped to a low as seven rounds per aircraft according to Japanese sources.
While it's "best" range was 1000 meters, it seems it's effective range was out to roughly 2200 meters, courtesy of Pythagoras.

What documentation do you have of the effective range of the Bofors being 5000 yards?

And that's one reason I hate the term "effective" range. It is too gray and results in many varying interpretations. I like a % of the maximum range unless some really hard facts are there abut "effective" range, as effective range is also determined by doctrine.
Steve Crandell
Senior Member
Posts: 954
Joined: Wed Feb 05, 2014 7:05 pm

Re: Japanese vs US AA capabilities

Post by Steve Crandell »

What is the rounds/kill of the 40mm Bofors at 12,000 yds, when the 5"/38 begins to engage the target? :)
Garyt
Senior Member
Posts: 274
Joined: Tue Dec 09, 2014 9:31 pm

Re: Japanese vs US AA capabilities

Post by Garyt »

The Bofors will put up 120 rounds/minute on average (but could go as high as 160)
Have to be level to get to 160 RPM, and that ain't going to happen in AA fire.
alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Japanese vs US AA capabilities

Post by alecsandros »

Garyt wrote: And a 40mm has about a 7% chance of killing a bird per minute of fire - a 5" (averaging both VT and non VT as not all were VT equipped) has about a 3.7% chance.
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.


I'm not sure what you mean here by "radar guided" 5" shells.
The guns were radar guided...
While it's "best" range was 1000 meters, it seems it's effective range was out to roughly 2200 meters, courtesy of Pythagoras.
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.
What documentation do you have of the effective range of the Bofors being 5000 yards?
http://www.ibiblio.org/hyperwar/USN/Adm ... Ord6R.html

It also mentions 160 rpm for the Bofors for up to 70* elevation.
Attachments
Effectiveness of IJN AA Gunfire.png
(124.33 KiB) Not downloaded yet
Francis Marliere
Senior Member
Posts: 276
Joined: Mon Oct 18, 2010 3:55 pm

Re: Japanese vs US AA capabilities

Post by Francis Marliere »

Gentlemen,

just a couple of things that I forgot to mention.

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.

As far as I understand things, it is not always correct to rate system (guns, directors, gunners, doctrine, sensors, ...) "good" or "bad". A system can be good in one situation and bad in another. I have already evocated the late war 5"/38, efficient but a bit slow to engage. The system was good against conventional attacks, but not against surprise ones. The British HCAS fire control was fine against level bombers but could not engage dive or torpedo bombers. The 0.50" machine-guns were almost useless against dive and torpedo bombers but proved effective against close range attacks (strafing, etc.).

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.

Best,

Francis
Garyt
Senior Member
Posts: 274
Joined: Tue Dec 09, 2014 9:31 pm

Re: Japanese vs US AA capabilities

Post by Garyt »

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.
http://www.ibiblio.org/hyperwar/USN/Adm ... Ord6R.html

It also mentions 160 rpm for the Bofors for up to 70* elevation.
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. :D

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.
Byron Angel
Senior Member
Posts: 1651
Joined: Sun Mar 06, 2011 1:06 am

Re: Japanese vs US AA capabilities

Post by Byron Angel »

..... I'd venture that the real issue with the 25mm was that the IJN was never able to provide better than iron sights for it.

B
Post Reply