What was the most effective naval anti-aircraft gun of WW2?

[dunmunro]

OK, I found another film clip of the 5.25" twin turrets, and they fire 3 twin gun salvos in 18 seconds:
http://www.wpafilmlibrary.com then enter 506410-1 in the search field.
starting at 01:10:54, again at 01:11:00 and again at 01:11:06

from 01:10:05 there is footage of about 4 or 5 salvos fired at 8 sec intervals. There's also some nice footage of Illustrious and Saratoga in the Indian or Pacific Oceans along with some footage of Richelieu. I am fairly certain that this was filmed aboard HMS Howe, in Aug/Sept 1944.

[Bgile]

OK, I found another film clip of the 5.25" twin turrets, and they fire 3 twin gun salvos in 18 seconds:
http://www.wpafilmlibrary.com then enter 506410-1 in the search field.
starting at 01:10:54, again at 01:11:00 and again at 01:11:06

from 01:10:05 there is footage of about 4 or 5 salvos fired at 8 sec intervals. There's also some nice footage of Illustrious and Saratoga in the Indian or Pacific Oceans along with some footage of Richelieu. I am fairly certain that this was filmed aboard HMS Howe, in Aug/Sept 1944.

Yes, that would be about 10 rounds per minute in the first instance and 7.5 rounds per minute in the second. That seems in accordance with published information.

[dunmunro]

Yes, that would be about 10 rounds per minute in the first instance and 7.5 rounds per minute in the second. That seems in accordance with published information.

The Gunnery Pocket Book does state 10-12 rpm, but this figure is disputed in some circles. We know that the gun can fire slower than this, but 10 RPM at the most difficult loading angle is a good indicator that the Gunnery Pocket Book is correct.

[dunmunro]

OK, I found another film clip of the 5.25" twin turrets, and they fire 3 twin gun salvos in 18 seconds:
http://www.wpafilmlibrary.com then enter 506410-1 in the search field.
starting at 01:10:54, again at 01:11:00 and again at 01:11:06

from 01:10:05 there is footage of about 4 or 5 salvos fired at 8 sec intervals. There's also some nice footage of Illustrious and Saratoga in the Indian or Pacific Oceans along with some footage of Richelieu. I am fairly certain that this was filmed aboard HMS Howe, in Aug/Sept 1944.

If you live outside the USA then select "USA" as country of search.

[dunmunro]

The document below lists the RoF of various USN weapons, for planning purposes, for a 5 minute period. This 'sustained' RoF is somewhat lower than the maximum figures commonly quoted for these weapons:

Battery______________5"/25__5"/38___6"/47__8"/55
RoF/Minute-5 minutes____10____10_____5______2

http://funsite.unc.edu/hyperwar/USMC/re ... index.html

[Bgile]

The document below lists the RoF of various USN weapons, for planning purposes, for a 5 minute period. This 'sustained' RoF is somewhat lower than the maximum figures commonly quoted for these weapons:

Battery______________5"/25__5"/38___6"/47__8"/55
RoF/Minute-5 minutes____10____10_____5______2

http://funsite.unc.edu/hyperwar/USMC/re ... index.html

The linked article is about shore bombardment. We already know the 5"/38 was capable of 25 rounds per minute. All gun crews slow down as they get tired, but that isn't really very relevant to air attack.

[dunmunro]

I doubt that 25RPM was possible during combat, but that's not the point. For bombardment purposes, the planners had to decide what was a reasonable RoF for extended periods, and I suspect that 10 RPM was chosen because higher RoFs might lead to overheating, with potentially fatal consequences for the gun crew. I know of at least one occasion a gun suffered a premature in the breech due to gun overheating during a bombardment off Guadalcanal, with fatal consequences for the turret crew.

[Bgile]

I doubt that 25RPM was possible during combat, but that's not the point. For bombardment purposes, the planners had to decide what was a reasonable RoF for extended periods, and I suspect that 10 RPM was chosen because higher RoFs might lead to overheating, with potentially fatal consequences for the gun crew. I know of at least one occasion a gun suffered a premature in the breech due to gun overheating during a bombardment off Guadalcanal, with fatal consequences for the turret crew.

What does shore bombardment have to do with this thread?

[Bgile]

When a guy says:

"Designed rate of fire was 15 rounds per gun per minute, but North Carolina's gun crews as well as those of some other ships, consistently achieved rates of up to 25 rounds per minute."

I don't think he is talking about just practice or he would have said so. He would have said "a few times in practice the fleet's best team managed to achieve 25 rounds per minute" or something similar. The whole discussion was in the context of antiaircraft fire.

[lwd]

If you look at page 4 of this thread you will note that the gunnery officer of HMS Dehli stated that the 5"/38 could maintian a rate of 25 rounds/minute. A reference link is given there.

[dunmunro]

If you look at page 4 of this thread you will note that the gunnery officer of HMS Dehli stated that the 5"/38 could maintian a rate of 25 rounds/minute. A reference link is given there.

I know that the gun cannot fire at 25 rpm for long periods because it would overheat, and even 15 RPM for 5 minutes became dangerous:

The rate of fire for the MK 38 mount was typically 15 rounds per barrel per minute. However, a really good gun crew could achieve 22 round per barrel per minute, however at that rate problems developed.
According to a Gunner's Mate (GM1) on the USS George K. Mac Kenzie (DD-836) they set a record when they fired 151 rounds in five minutes from their 5 inch/38 caliber MK 38 twin mount but then had to cool the barrels off with the ship's fire hose. This was in preparation for a Marine landing on a small peninsula not far from Da Nang. The Marine spotter in his small Piper aircraft called the landing off. He said there was not a tree left standing and nothing left to hide the enemy!
Further, the barrel of the 5 inch/38 caliber gun did wear out with this type of use. While specifications called for a barrel service life of 4600 rounds, using basic rounds the tube life expectancy on-ship was about 1,500 rounds but as muzzle velocity increased, a drop of about 800 rounds was to be expected in tube life. Replacing these gun barrels on the FRAM destroyer was not an easy thing: The method involved a special wrench which attached at the base of the barrel, and a 20 LB sledge hammer. The barrel - unscrewed- seen left and took approximately 8 hrs per gun vs. the 1 hr for the 5 inch/54 cal MK 42 gun. Disassembled from the turret, the barrel weighed some 3,991 lbs. This was the process for the forward mounts. For the Aft 5" mount at the fantail (Mount 53), the complete gun mount was completely taken off the ship and taken to the overhaul shop. A month later it was brought back and it was like brand new.
http://www.gyrodynehelicopters.com/5_in ... l__gun.htm

I was trying to show how the RoF has to fall when guns are fired for extended periods. I have read a lot of combat reports and none have ever stated 25 RPM.

On the morning of August 7th the trans-
ports landed Marines on Guadalcanal and
Tulagi under cover of shore bombardment
by covering destroyers and cruisers. Pre-
ceded only by destroyer screen the SAN
JUAN led the transports in to Tulagi Island
with her eight twin mounts firing olmost
three thousand rounds of five-inch ammu-
nition. At the height of action the forward
mount was put out of action when the left
barrel overheated; causing a premature
shell explosion. When the smoke hod
cleared away five men had answered their
last muster and twelve more were carried
below to sick boy. The Japanese retaliated
with an air attack on August 8th in which
the SAN JUAN proved her designers' faith
well founded. Capta i n Mahe r opposed the
display of ''flags'' until official confirma-
tion had been received so the ''Panther's''
flanks remained unbranded. p.19
The Panther Strikes. (The story of USS San Juan CL 54)

[Bgile]

I don't doubt that if the guns were fired that way for extended periods there would be serious problems.

[lwd]

... I know that the gun cannot fire at 25 rpm for long periods because it would overheat, and even 15 RPM for 5 minutes became dangerous:

Kind of depends on what you mean by "long periods" certainly maintaining maximum rate of fire is not easy on either the crew or the gun however let's take a look at your quote:

... According to a Gunner's Mate (GM1) on the USS George K. Mac Kenzie (DD-836) they set a record when they fired 151 rounds in five minutes from their 5 inch/38 caliber MK 38 twin mount but then had to cool the barrels off with the ship's fire hose. ...

Looking at: http://www.navweaps.com/Weapons/WNUS_5-38_mk12.htm most DD's carried less than 400 rounds so in this case they shot up ~20% of thier ammo in 5 minutes. Typically one wouldn't expect continuous fire at a arial target either. The range of the gun is about 10 miles so if an attacking plane is moving 180 mph that's about 3 miles per minute or just over 3 minutes from max range to directly overhead. I don't see any pressing need for more than about 5 minutes of fire.

I was trying to show how the RoF has to fall when guns are fired for extended periods. I have read a lot of combat reports and none have ever stated 25 RPM.

Has anyone disputed this? Indeed since the guns aren't automatic fatigue will start to play a roll after a minute or two. The question becomes how relevant it is. The example above was a fire support mission which means that the target is fixed and nothings going to slow one down. VS planes I would expect engagements to mostly be less than that. There's also the fact that if you were firing at 25 rpm even the larger magazined destroyers would run out of ammo in not much over 15 minutes. If you are expecting or even want to be able to respond to multiple attacks over the coures of the day that's not good. On the other hand being able to get rates up in the 25rpm range for a brief critical period of time can be quite useful.

[Bgile]

I wouldn't expect that rate of fire to be maintained more than a minute or so. It's got to be very tiring.

[dunmunro]

The Bofors was reckoned to be twice as effective as the pom-pom against
torpedo planes, though not much better against very close targets such as kamikazes.
Naval Weapons of WW2, p.80

This is commonly stated, yet if we examine the actual ballistics and shell weight/burster size, it seems to be based upon a worst case scenario for the pom-pom. Assuming equal fire control the relative accuracy should be equivalent to the Average Projectile Velocity (APV) over the distance to the target, against a crossing target:

data from 40mm bofors USN range table*

Bofors
3k yds = 2800mv + 1170sv = 3970/2 = 1985apv
4k yds = 2800mv + 972sv = 3850/2 = 1885apv
2 pdr (estimated from the USN bofors range table)
3k yds = 2300mv + 1000sv = 3300 = 1650apv
4 k yds = 2300mv + 890sv = 3190 = 1595apv

accuracy ratio at 3k yds = 1985/1650 = 1.2
accuracy ratio at 4k yds = 1885/1595 = 1.18

basically, the Bofors should be about 20% more accurate than a pom-pom at 4k yds, against a crossing target. The Bofors has about a 5 to 50% better RoF** (depending on gun elevation) and maybe 10% better lethality per hit (although a single hit from either might be sufficient for many targets) so the total advantage for the Bofors at low elevation (at low elevation Bofors RoF = ~145 RPM, falling to 120 RPM at high elevation) is about 1.95x compared to an pom-pom in controlled fire (~97 RPM) and about 1.7x compared to pom-pom in automatic fire (115 RPM) against a fully crossing target, but this advantage would decline as the target approaches an intercept course to about 1.65x versus a controlled fire pom-pom and 1.4x over a pom-pom in automatic fire, and about 1.35 to 1.15x against a high elevation target versus a pom-pom in controlled and automatic fire, respectively.
Against a directly threatening target (which probably accounted for the majority of engaged targets by any ship) the Bofors probably averaged to about 1.5 to 1.25x as effective as a pom-pom but then again it was about 20% heavier, gun for gun than the pom-pom. The actual advantage of the Bofors is therefore, rather slender, most of the time.

* http://www.eugeneleeslover.com/ENGINEER ... idged.html
-IMPORTANT NOTE- the above range table contains a serious mistake for the 40mm Bofors!!! Note that the SV at 500 yds = 2800fps! This is completely wrong and it should be about 2450 fps so I had to estimate the SV for the above ranges by taking the values from the 3500 and 4500 yd entries. This mistake appears to be repeated by Navweaps.com and by Campbell in Naval Weapons of WW2.


**Campbell states that a skillful Bofors loader might be able to fire 24 rounds (10 seconds at low elevation and ~145 RPM) without pause so over a ~12 second period the Effective RoF might be less than a pom-pom.