Japanese vs US AA capabilities

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Garyt
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Japanese vs US AA capabilities

Postby Garyt » Wed Dec 17, 2014 9:41 pm

This is one of the areas of the Pacific War where the Japanese ran a far second from the US AA capability. And when I say AA capability, I not only mean what amount and the accuracy of shells that could be put into the air, but also the effects of these shells upon enemy planes, causing the durability of planes or lack of to be part of the equation. I'll stay away from CAP capabilities, but to address it rather quickly Japan did not have the organization of US CAP, largely due to US radar superiority, being able to get altitudes of incoming formations earlier, radio control or lack of,all these combining to make it difficult to vector the right amount of CAP to the right place at the right time. Put simply, better control of CAP would have allowed Japanese fighters to attack the Dive Bombers at Midway, which likely would have had a major bearing on that battle.

Anyway, Back to the AA differential:

1) Heavy AA - The US used the 5"/38 for the most part is it's heavy AA weapon. Best dual purpose weapon of the war. Good training/elevation speeds, a robust projectile, a power rammer that allowed it to be loaded at high levels of elevation and cut down on crew fatigue, and a very high rate of fire, 15-22 Rounds per minute if it had an internal hoist (many, but not all mountings had internal hoists). Add to this later radar directed fire, and it was easily the best AA medium caliber naval gun of the war. Of course, than you have to throw on the proximity fuse. Even with a moderately high "dud" rate compared to standard fusing, it still at least doubled the effectiveness of these weapons.

Japanese Heavy AA - A range of guns performed this role. The Destroyer mounted 5"/50 has perhaps the worst. Horrid training/elevation rates, a capped elevation rate as low as 40 degrees in some models, no power ramming, a rate of fire of about 10 rpm. While as a surface weapon it was roughly equivalent to the US 5"/38, even superior as a surface weapon in some ways, as a AA weapon it was terrible. Perhaps the term "dual purpose" barely applies to this weapon.

The other common Japanese Heavy AA weapons, the 5"/45 and the 4.7"/40 were OK, but rather unremarkable. They had a slower train/elevation than the US weapon and a lower rate of fire. Add to this a lack of a proximity fuse and inferior radar fire control, and it was easily outclassed by the US weapon.

The one Japanese weapon that indeed was effective as an AA weapon was the 3.9"/60. High train/elevation speeds, rate of fire equal to the US 5"/38. A slightly small shell of course, but a very good weapon. Only thing that prevented it from being as good as the US 5"/38 was inferior radar fire control and lack of a proximity fuse. Unfortunately for the Japanese, these guns were somewhat uncommon in comparison to other AA weapons.

2) Light AA - I'm going to leave out the various machine guns and only focus on 20mm or greater weapons.

Really the only Japanese light AA weapon of the war was the much maligned 25mm/60. Strictly as a gun only, it seemed to be fine. It had a good muzzle velocity and a maximum rate of fire in the 240 range. Unforunately there were other problems. It's loading system lowered it's effective rate of fire to 110rpm - a belt fed or feeding system similar to the 40mm bofors would have helped. It's 3 barreled mounts shook excessively, I'd think this was a problem with the mount, not the gun, the mount not being substantial enough. Might have had something to do with the Japanese tying to put as many 25mm's on a ship as possible. Overall though, because of the problems listed above, and adding this to a low train/elevation speed on the triple mounts and a sub par sighting system and it was not overly effective.

US light AA - We have the 20mm Oerlikon, the 1.1"/75, and the 40mm Bofors. The Bofors was the best light AA weapon of the war, delivering a large 40mm projectile with a 120-160 ROF. THe Oerlikon was a nice weapon too, a 250-320 practical ROF. By the end of the war these were not great against kamikazes, and were replaced when possible with the 40mm Bofors. The US 1.1" was discarded early in favor of the Oerlikon. Seemed like a decent weapon that was discarded ealry, it's effective rate of fire was not great at 100 rounds per minute, and apparently it's fire director was not on par with later fire directors, but that I htink would have been a problem with any AA weapon at that early time of the war.

3) Radar - Japan usually seemed to be roughly about 2 years behind the US when it came to radar during the war, which is a lifetime for wartime technology, as the P47 entered production only about 2 years after the P40. The Japanese even had radar controlled fire directors for main naval weapons before the end of the war, though true "blindfire" fire direction was in the experimental stage. But this meant that the US always had a nice edge in radar technology for fire direction, and Japan never developed anything similar to the proximity fuse.

4) Plane Durability - A huge advantage to the US. Rather simple to state, the Japanese generally did not have self sealing fuel tanks until late in the war, I don't think any of their carrier based strike aircraft ever had self sealing fuel tanks or armor, deeming range much more important. In comparison, I think almost all US carrier based aircraft had armor and self sealing fuel tanks even at the outset of the war.

What is interesting about this is that looking at the first part of the war, the carrier battles of Croal Sea, Midway and Santa Cruz, the Japanese would suffer more casualties than the US. This is even though their pilots were arguably better during this time period, and the Zero was considered superior to the Wildcat in air-to-air combat.

Combine this with the Japanese very slow rate of pilot replentishment, and it's pretty clear why during the Marianas battle the Japanese were no match at all for the US in Carrier clashes. I think it would have made far more sense for the Japanese to focus less on range and more on pilot survival.

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Re: Japanese vs US AA capabilities

Postby Steve Crandell » Wed Dec 17, 2014 10:05 pm

Good post, and I think you summarized it pretty well. One thing I'd add is that with the advent of the Kamikaze even the 40mm Bofors was marginal because it's effective range wasn't long enough to engage one with a really good probability of shooting it down before it hit the firing ship. The USN planned to replace it with the 3"/50 using VT fuzes at about 1 for 3 guns, but that didn't really get going in large numbers until post war with the new twin mount.

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Re: Japanese vs US AA capabilities

Postby Garyt » Thu Dec 18, 2014 12:50 am

That 3" was a pretty mean weapon. I think it had a rate of fire of 50 rpm's or so,combine with a proximity fuse. I don't think it was operational until 1948, but had the invasion of Japan came about it may well have been pressed into service sooner.

with the advent of the Kamikaze even the 40mm Bofors was marginal because it's effective range wasn't long enough to engage one with a really good probability of shooting it down before it hit the firing ship.


The Oerlikon had this problem as well to a greater extent of course :D

Good post, and I think you summarized it pretty well.


Thanks. I've always been shocked as to how badly the Japanese were set up on Naval AA compared to the US.

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Re: Japanese vs US AA capabilities

Postby aurora » Thu Dec 18, 2014 9:26 am

Apologies for going off topic

The British 5.25" Dual Purpose gun

The RN Gunnery Pocket Book published in 1945 states:

These guns are combined High Angle and Low Angle Guns. The Mark II Mounting is found in all Dido class cruisers. The Mark I Mounting is found in King George V class battleships, where they fulfil the combined functions of H.A. Long Range Armament and Secondary Armament against surface craft. The main differences between the two mountings lie in the arrangements of the shellrooms and magazines, and the supply of ammunition to the guns. In this chapter, only the Mark II Mounting, as found in Dido class cruisers, is discussed. The 5.25 in. calibre with separate ammunition is used for dual High Angle and Low Angle Armament, since it gives the reasonable maximum weight of shell which can be loaded by the average gun's crew for sustained periods at all angles of elevation. The maximum rate of fire should be 10-12 rounds per minute
Last edited by aurora on Thu Dec 18, 2014 9:45 am, edited 1 time in total.
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Re: Japanese vs US AA capabilities

Postby aurora » Thu Dec 18, 2014 9:43 am

The Royal Navy;s Chicago Piano-the multi barrelled pom pom

The Royal Navy judged the pom-pom's effectiveness to range from about half that of the Bofors, per gun, against torpedo planes to about equal against Kamikaze attackers. It was a ubiquitous weapon that outnumbered the Bofors gun in Commonwealth naval service up to the end of World War II and it shot down many Axis aircraft. Later innovations such as Remote Power Control (RPC) coupled to a radar-equipped tachymetric (speed predicting) director increased the accuracy enormously and problems with the fuses and reliability were also remedied. The single mountings received a reprieve toward the end of the war as the 20 mm Oerlikon guns had insufficient stopping power to counter Japanese kamikaze aircraft and there were insufficient numbers of Bofors guns to meet demand.

Calibre: 40 mm L/39
Shell Weight: 2 lb. (980 g) or 1.8 lb. (820 g) for High-Velocity (HV) round
Rate of Fire: 115 rpm fully automatic
Effective Range: 3,800 yards (3,475 m) or 5,000 yards (4,572 m) HV
Effective Ceiling (HV): 13,300 feet (3,960 m)
Muzzle Velocity: 2,040 ft/s (622 m/s) or 2400 ft/s (732 m/s) for HV [19]
For more extensive technical data, see 2-pdr Mark VIII at Navweaps.com
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Re: Japanese vs US AA capabilities

Postby Garyt » Fri Dec 19, 2014 10:52 pm

The British 5.25" Dual Purpose gun


Not a bad weapon, but hardly the mainstay of the British dual purpose AA park. They had a lot of dual purpose weapons, kind of a mixed bag like the Japanese had, including a 4" weapon or two, a few 4.5" weapons, and the 5.25" weapon you mention. That (the 5.25") is a decent weapon, but it's rate of fire puts it in line with the Japanese 5" weapons.

The other dual purpose weapon have varying rates of fire, one of the 4" having a 15-20 rate of fire, the others slower.

Overall, I'd put their DP weapons in a class similar to the Japanese, though probably with better fire control.

The 40mm Pom-Pom is another story, a rather low ROF compared to the Bofors, and a low muzzle velocity, one of the variants has an extremely low muzzle velocity.

For light AA fire, I'd have to put british vessels no more effective than the Japanese in AA, except again perhaps better fire control for the British. And the one thing hat the Japanese did to compensate for inadequate AA fire - completely load their vessels with as much light AA as possible - the British did not do this.

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Re: Japanese vs US AA capabilities

Postby aurora » Sat Dec 20, 2014 10:34 am

Unfortunately, aircraft were not available to the HMS Prince of Wales and HMS Repulse when the two capital ships were attacked by a massive force of bombers and torpedo aircraft. The ships pom-poms were also hampered by ammunition which had degraded in the heat and humidity of the tropics. HMS Repulse’s pom-poms shot down two Japanese aircraft, but the newer 40mm Bofors autocannon made a better account of itself with its greater reliability, tracer ammunition and gyroscopic sights.

Autocannon like the Swedish Bofors and the smaller 20mm Swiss-designed Oerlikon were under production in Britain but were not available at the beginning of the war. The Bofors had begun to become available from 1942, and quickly showed itself to be an improvement on the pom-pom. British naval versions of WW2 fired rounds from clips of four, and could theoretically maintain a firing rate of 120 rounds per minute – although this required a great deal of dexterity in the gun crew to replace the clip every two seconds.

The Oerlikon was an effective short-range weapon, and suitable for mounting on light and coastal vessels such as air-sea rescue launches corvettes,sloops and submarines – in fact the weight of the basic gun compared favourably with that of the .50in Browning machine gun. It could fire up to 500 rounds per minute, from magazines that could carry up to 60 rounds and was available to the RN in single and twin mountings (German derived weapons commonly used quadruple mountings). The 20mm shell was able to penetrate aircraft armour, unlike rifle-calibre machine gun bullets.The Oerlikon was a successful weapon, and in greatly developed versions is still in service, though on larger vessels it tended to be supplanted by the Bofors due to the latter’s greater stopping power. This feature was of great use against Kamikaze attacks in the Pacific.

From before the Second World War, another way of strengthening the anti-aircraft armament of warships was to make the secondary armament or even primary armament dual purpose, with high-angle mountings and different types of ammunition available for different roles. These were heavier weapons which were intended more to destroy aircraft through detonating a shell at a specified altitude, throwing shrapnel across a wide area.

The introduction of dual-use weapons helped to minimise the amount of specialist anti-aircraft weaponry that ships were required to carry, and was more efficient in terms of the crew as well. British 4in, 4.5in and 5.25in guns were mounted to warships with air defence in mind as well as anti-ship and naval gunnery support functions. The BL 4.5in gun was developed as a dual-use weapon for aircraft carriers, to defend against destroyer or torpedo-boat attack and air strikes, and was later developed with a different mounting for destroyers that could elevate up to 55°.
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Re: Japanese vs US AA capabilities

Postby Garyt » Sat Dec 20, 2014 4:32 pm

The Oerlikon was an effective short-range weapon, and suitable for mounting on light and coastal vessels such as air-sea rescue launches corvettes,sloops and submarines – in fact the weight of the basic gun compared favourably with that of the .50in Browning machine gun. It could fire up to 500 rounds per minute, from magazines that could carry up to 60 rounds and was available to the RN in single and twin mountings (German derived weapons commonly used quadruple mountings). The 20mm shell was able to penetrate aircraft armour, unlike rifle-calibre machine gun bullets.The Oerlikon was a successful weapon, and in greatly developed versions is still in service, though on larger vessels it tended to be supplanted by the Bofors due to the latter’s greater stopping power. This feature was of great use against Kamikaze attacks in the Pacific.


The Oerlikon 20mm was a pretty nice weapon that I think gets a bad rap, as the article you pulled points to Aurora.

The Allies were extremely concerned with Kamikazes at the end of the war, as it was about the only Japanese attack that had any success at this late stage.

The 20mm had it's drawbacks, mostly range, but it had some stopping power, as a 20mm mounted in a fighter craft was considered heavy armament. The one thing it was not great at was completely destroying a plane with a round or two, which is what you needed to do to a kamikaze.

But it put cannon sized projectiles in the air, though the 500 rounds per minute is overly optimistic. 450 was max cyclical rate, and in practice it was 270-320 rounds per minute, still a great rate of fire. The .50 cal browning water cooled had a cyclical rate of 450-600, which is better of course, but we are talking about 49 gram projectile from the Browning vs a 123 gram projectile from the Oerlikon, and the 20mm ammo was high explosive contact fused. Still required to make contavt with it's target, but a lot more stopping power than a .50 caliber. The .50 cal did have decent range, both weapons had an effective range of about 1200 yards.

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Re: Japanese vs US AA capabilities

Postby aurora » Sat Dec 20, 2014 4:47 pm

Quote Garyt
"The Oerlikon 20mm was a pretty nice weapon that I think gets a bad rap, as the article you pulled points to Aurora".

Not at all sure what you inferring to Gary in the above statement-I get the impression that it points to me-or am I imagining what I read- Right/Wrong????? I hasten to add no offence intended. :? :? :?
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Re: Japanese vs US AA capabilities

Postby Garyt » Sat Dec 20, 2014 5:27 pm

Was that your own words or a copy paste Aurora?

I thought it was a copy paste, my error if it was not.

My only point is the Oerlikon is much maligned due to it's performance against kamikazes, but that was a very unusual situation and it's effectiveness against conventional attack is often overlooked.

Here is a very interesting site regarding types of US anti aircraft from WW2, rounds fired, kills, etc. etc.

http://www.ibiblio.org/hyperwar/USN/rep ... ex.html#II

You can make some calculations using the rate of fire of various weapons, and then get in idea for their "kills per minute". Can even take it a step further and look and weight of guns and mounts, plus the weight of ammo for x amount of minutes, and determine which was the best gun and which was best for it's weight. The Oerlikon will do decent here.

One important thing though - all AA is not created equal, and different types of AA have different function. Light AA is mostly for local defense - it is very limited in providing fire support for near by vessels. Heavy AA on dual purpose weapons does a handful of things, as a main armament on destroyers, or as a lighter more rapid firing weapon for use against light cruisers and destroyers. And of course AA fire support for other vessels. It's real tough to compare light AA vs Heavy AA.

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Re: Japanese vs US AA capabilities

Postby aurora » Sat Dec 20, 2014 5:35 pm

Quote Gary
"One important thing though - all AA is not created equal, and different types of AA have different function. Light AA is mostly for local defense - it is very limited in providing fire support for near by vessels. Heavy AA on dual purpose weapons does a handful of things, as a main armament on destroyers, or as a lighter more rapid firing weapon for use against light cruisers and destroyers. And of course AA fire support for other vessels. It's real tough to compare light AA vs Heavy AA".

You make some very profound points here Gary, because AA capability is a complex entity and covers a multitude of circumstances; and as you say it is tough comparing Light and Heavy AA :think: :think:
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Re: Japanese vs US AA capabilities

Postby Steve Crandell » Sat Dec 20, 2014 6:03 pm

From Capt Ben W. Blee, USN(ret) "Battleship North Carolina" on kamikaze attacks (He was at that time the ship's intelligence officer):

"I cannot deny the fear that gripped me and others in the CIC during a kamikaze attack. We could see nothing, so all we knew was what we could hear. First warning of a kamikaze attack was usually the sudden, ear splitting crack of a single 5-inch gun. Opening range could be anywhere from 12,000 yards down to perhaps half that distance, depending on how much warning preceded the attack. Two or three more hesitant rounds might follow, as the gunners limbered up. Then, in a thunderous crescendo, all ten 5-inch guns on the ship's engaged side would open fire, leaving no doubt that the shooting was deadly serious.

The sound of the rapid-firing 5-inchers was deafening, even for those of us inside the CIC. Nothing else could be heard. Unable to banter or commiserate with each other, as men in combat are prone to do, each man could only withdraw into himself, relying on his own resource of courage. With the threat of a fiery death suddenly staring us in the face, staying cool required the utmost willpower. With the task force steaming at high speed, the entire ship vibrated and rattled in time with the churing propellers. This, along with the usual violent evasive maneuvers, added suspense and urgency to the unseen danger screaming toward us from above. As the range closed, the 40-mm guns opened up with a steady ka-boom! ka-boom! ka-boom! more felt than heard above the sounds of the 5-inch. This meant that the pilot was within a couple of miles of us and well into his dive. Finally, with only seconds left before the crash, as many as 50 short-range 20-mm guns began their fierce popping stacatto. At that moment, even the most stoic of the listeners would grit his teeth, shut his eyes and pray. In these circumstances it seemed to me that courage was nothing more - and nothing less - than the willpower to shut off all thought of what might happen, to force your mind to concentrate solely on what had to be done and to do it."

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Re: Japanese vs US AA capabilities

Postby Steve Crandell » Sat Dec 20, 2014 6:06 pm

I might add that North Carolina had an actual CIC. It was added at some point late in the war, and it was a large room added behind the bridge which contained about 15 to 20 men and numerous radar repeaters.

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Re: Japanese vs US AA capabilities

Postby aurora » Sat Dec 20, 2014 6:48 pm

Is that a Command and Control Centre Steve?? My thanks for the excellent story by Capt.Ben W Blee USN one time Intel. Officer in USS North Carolina BB

"This meant that the pilot was within a couple of miles of us and well into his dive. Finally, with only seconds left before the crash, as many as 50 short-range 20-mm guns began their fierce popping stacatto. At that moment, even the most stoic of the listeners would grit his teeth, shut his eyes and pray. In these circumstances it seemed to me that courage was nothing more - and nothing less - than the willpower to shut off all thought of what might happen, to force your mind to concentrate solely on what had to be done and to do it."

TERRIFYING and HEART STOPPING!!!
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Re: Japanese vs US AA capabilities

Postby Steve Crandell » Sat Dec 20, 2014 7:34 pm

aurora wrote:Is that a Command and Control Centre Steve?? My thanks for the excellent story by Capt.Ben W Blee USN one time Intel. Officer in USS North Carolina BB


Combat Information Center; one of the first attempts at what we have on modern naval vessels.


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