Destroyers.....

[parsifal]

It certainly is possible to create scenarios where high traverse rates are useful, but typical AA engagements involve picking the aircraft up when it was still considerable ways from the target, and usually before the point where it has to steady on it's bomb run, and 10degs/sec is quite adequate for that. This was especially true after radar became widespread in 1941.

True, I agree, but this doesnt change the same basic disadvantage of the 4.7". I ran a different scenario.....which I have sketched and tried to optimise the DDs firing position. I can post the worksheet if you are interested (I wish I had kept some PP plot sheet which are excellent for working this sort of stuff out...of course nowadays its all worked out electronically). This is still an anvil attack, one group from dead ahead and another from the port beam, about 60 deg off the bow. I assumed an initial engagement range of 7000m for both the head on attack and a beam attack, with (as i said) the beam attack 60 deg off the bow coming in on the port side of the target. the target is assumed to be steaming 20kts, whilst the DD is steaming 30 kts. The a/c are attacking at 200mph, launch range is still 2000m. the DD is placed on the port side of the target about 1500m from the target (a typical TD) , so that the attackers will pass just forward of the DD and be in launch position about 600m from the DD. This is about as optimal for a DD in a realitic situation as I can achieve, whilst still also being realistic about the aircraft tactics and capability.

To get into ideal firing position, the DD has to turn 30 deg to starboard and the guns have to traverse 90 deg. Again assuming a 5 second command delay and as SR points out some estimate of accelaration delay (I am guessing about 3 secs for the slower traversing turret, and about 1 sec for the faster 5/38 turret for a 90 deg traverse), we have a 17 second delay for the 4.7 turret. I calculate that it will take 43 secs for the beam attack to get into firing posn, but firing time for the DD will be reduced to 26 secs after allowing for all of the above. At 10 rpm that means they will get off 4-5 rounds before launch.

For the equivalent 5/38, everything is the same, except time delay and rof. Because of the accelaration issue and higher traverse rate, the gun will be in firing position 9 secs after initial orders are given. That gives them 34secs of firing time, or 17 rounds at max rof.

of course this is all theoretical, but even as atheoretical excercise, it amply demonstrates one of the basic disadvantages of the 4.7 mounting as a "DP" mount. It makes no real difference in relaistic situations the 4.7 will always perform significantly less efficiently than the 5/38.

 

[Glider]

B)The Porter/Somers class, as built, had a LA only Mk 35 director with no AA capability - see Friedman's The U. S. Destroyers: An Illustrated Design History, p87.

You are correct my info was wrong

C

D: Here's the engagement envelope of the 4.7in twin:
View attachment 224306

The level bombers that attacked HMS Prince of Wales and USS Hornet flew at 9000ft and you can see that a 4.7in Tribal-JKM destroyer could have engaged them continuously, if placed on a screen around the ships being attacked. Dive bombers could be engaged prior to dropping their bombs and during their bomb run via barrage placed over the ship being attacked. A barrage, in naval terms, is created by firing the guns with a fuze setting designed to burst at a fixed point in front of the attacking aircraft's path.

I couldn't open the attachment but get the general picture. Would it be faor to say that your belief is that the would be able to help defend other ships, but with the lack of high angle would be defenceless against dive bombers to defend themselves.

e) The Australian tribals retained 8 main guns, their quad pom-pom and their TTs. They didn't reduce their gun armament. In 1940/41 the RN didn't have the option to fit single Bofors guns.

Absolutely agree with you. In 1940/41 no one had the chance to rearm with 40mm. The point was that the Tribal as a design could and did accept increased AA guns without losing any of their main weapons because of weight consideration. The Aussie Tribals as you uyourself point aut, confirm that view.

f) Naval weapons of WW2, p50 shows the fuze receiver on the 4.7in twin mount along with the fuze setting pedestal - just as the schematic states in my earlier post; so it has on mount fuze receiver/setter, and it is controlled by an AA FC computer, which in turn was fed data by a HA director - I have pointed this out and supplied hard data via solid references to back it up and it's time you simply admit that it was a DP mounting.

The difference is that the AA director is high angle but the gun isn't. The gun is a low angle that will work against torpedo bombers and as you point out help other ships, but no more.

I don't give a hoot for Navweaps editorial comments. It was a DP gun controlled via an AA FC computer. Navweaps is simply wrong. I've already given examples of 4.7in guns being used against aircraft while being controlled by the AA computer but here's a drawing and photo of the mount showing the AA fuze setter:
View attachment 224307

Here we disagree, all I say is that those fittings would help against a low altitude attack. The problem I have with your argument is that you don't awnser the difficult questions just restate your view.
Question 1 Why did the RN install a twin 4in HA gun when there was no issue with weight.
Question 2 Why did the RCN build that last two destroyers with 8 x 4in HA guns if the 4.7 was a true DP gun
Question 3 Why did the RN develop proper DP guns if the original ones were true DP guns

I earlier pointed out that Lundstrom's two volume study the USN in the Pacific, First Team, hi-lights the poor showing of USN AA was during 1942, so it seems that the USN simply wasted a lot of weight and money on AA systems that seem advanced, on paper, but as per Maury's experience, just weren't very effective:

Your forgetting one mportant thing. In 1942 the USN were new to combat. It would be foolish to pretend that ships crews were fully effective. Also no one would disagree that HAA of any type only became really effective with the proximity fuse.
Its also worth pointing out that in 1941/2 the US 5in and mk 37 director was fitted to HMS Delhi and the RN were so impressed that they tried to purchase more units for fitting in RN warships but production was already committed to USN needs. Cleary the RN who had considerable experience of combat at this stage disagreed with him.

I'll bet the above Admiral's comments will never appear on Navweaps or this recommendation from Yorktown after Midway:

I admit to not understanding your poosition on this. The quote you posted was very clear 5inL38 guns are very effective at long ranges and should be retained in AA ships

 

[RCAFson]

You are correct my info was wrong

C

a)I couldn't open the attachment but get the general picture. Would it be faor to say that your belief is that the would be able to help defend other ships, but with the lack of high angle would be defenceless against dive bombers to defend themselves.

b) Absolutely agree with you. In 1940/41 no one had the chance to rearm with 40mm. The point was that the Tribal as a design could and did accept increased AA guns without losing any of their main weapons because of weight consideration. The Aussie Tribals as you uyourself point aut, confirm that view.

The difference is that the AA director is high angle but the gun isn't. The gun is a low angle that will work against torpedo bombers and as you point out help other ships, but no more.

c) Here we disagree, all I say is that those fittings would help against a low altitude attack. The problem I have with your argument is that you don't awnser the difficult questions just restate your view.
Question 1 Why did the RN install a twin 4in HA gun when there was no issue with weight.
Question 2 Why did the RCN build that last two destroyers with 8 x 4in HA guns if the 4.7 was a true DP gun
Question 3 Why did the RN develop proper DP guns if the original ones were true DP guns

d) Your forgetting one mportant thing. In 1942 the USN were new to combat. It would be foolish to pretend that ships crews were fully effective. Also no one would disagree that HAA of any type only became really effective with the proximity fuse.
Its also worth pointing out that in 1941/2 the US 5in and mk 37 director was fitted to HMS Delhi and the RN were so impressed that they tried to purchase more units for fitting in RN warships but production was already committed to USN needs. Cleary the RN who had considerable experience of combat at this stage disagreed with him.
e)I admit to not understanding your poosition on this. The quote you posted was very clear 5inL38 guns are very effective at long ranges and should be retained in AA ships

a) I'll try again:

They wouldn't be defenceless because they still have a quad 40mm pom-pom, and they can still engage the target to within a minimum range depending on it's altitude

b) But in 1941 adding a quad pom-pom meant removing a gun mount or all the TTs.
c) The RN 50lb 4.7 shell was obsolete (designed pre WW1), with poor streamlining and thus range and no new designs were forthcoming. The RN 4" twin actually out-ranges the 4.7 twin but it has the draw back that it fires a much lighter shell so the RCN must have decided to simply accept the 4in disadvanatges and move to an entire 4in armament. With the advent of VT ammo, high angle, close range fire became a feasible proposition, when it wasn't using mechanical time fuzes.

D) C'mon Coral Sea and Midway were 6 and 7 months into the war - about the same as the RN in Norway. The point is that the USN didn't find AA fire abovc 40degs to be very effective and the CO of Yorktown called for the vaunted 5in/38 to be removed entirely.

e) and at long ranges, 40deg elevation was just fine.
.

 

[RCAFson]

My whole point is that 40 deg guns were not useless - they could and were used to engage aircraft. Adding a heavy, expensive, complex HA mount with complex FC computer didn't turn USN destroyers into invincible AA platforms, and it seems that they didn't really do any better than RN destroyers with FKC FC and 40deg gun elevation.

 

[parsifal]

My whole point is that 40 deg guns were not useless - they could and were used to engage aircraft.

Yes, you have shown that. I would be happy to agree or concede that point.

Adding a heavy, expensive, complex HA mount with complex FC computer didn't turn USN destroyers into invincible AA platforms,

They werent heavy, compared to their nearest equivalents. Id agree they (US DDs) were not invincible AA platforms, but neither can we discount that they were better than the RN. Most contemporary opinions are that they were better.

and it seems that they didn't really do any better than RN destroyers with FKC FC and 40deg gun elevation.

By no stretch of the imgination, no assuaging of the facts, no papering over of the enormous doubts raised in the discussions can you make this claim. From the technical assessment a 40 degree elevation was a big problem, the slow rate of traverse another problem, the slow rof another. all this suggests a less capable weapon system in the AA role. Where you might have a valid point, but have not really brouight the point out, is the inherent weakness of the 5/38 in the anti-surface role. The USN gave a lot of ground in this regard to gain some advantage in the AA role. Despite your valiant attenmpts at rebuttal, my opinion is that you have NOT shown the Brit DDs as comparable AA platforms. i think on the basis of probabilities they (the brit DDs) were significantly weaker in this regard.

 

[RCAFson]

Despite your valiant attenmpts at rebuttal, my opinion is that you have NOT shown the Brit DDs as comparable AA platforms. i think on the basis of probabilities they (the brit DDs) were significantly weaker in this regard.

The thing that we haven't looked at, is that the Tribal and later classes had a much heavier CIWS than contemporary USN destroyers, and they were able to do this because they saved weight by having a LA main armament.

If you think that USN destroyers did better, then where's your proof? We know from Lundstrom that USN destroyer AA just wasn't that effective before VT ammo was introduced. Given all their bells and whistles, USN AA FC must have seemed impressive, but the reality is that it shot down very few aircraft.

 

[Glider]

a) I'll try again:

View attachment 224333
They wouldn't be defenceless because they still have a quad 40mm pom-pom, and they can still engage the target to within a minimum range depending on it's altitude.

So you basically agree that the Tribal would be defencless against a dive bomber until the bomber came within range of the 2pd. Which would give the 2pd seconds to shoot it down, at a rough estimate about five seconds.

b) But in 1941 adding a quad pom-pom meant removing a gun mount or all the TTs..

But according to your theory the Tribals didn't need to switch to anything. You see the 4.7 as a good DP gun and we know that the Tribal didn't have any weight issues so it wasn't because of that. So why would they want to add a quad 2pd or a twin 4in. When the 4in was installed that only changes to the LAA fire was swopping the 0.5in for 20mm's..

c) The RN 50lb 4.7 shell was obsolete (designed pre WW1), with poor streamlining and thus range and no new designs were forthcoming. The RN 4" twin actually out-ranges the 4.7 twin but it has the draw back that it fires a much lighter shell so the RCN must have decided to simply accept the 4in disadvanatges and move to an entire 4in armament. With the advent of VT ammo, high angle, close range fire became a feasible proposition, when it wasn't using mechanical time fuzes..

So now your saying that the 4.7 shell was obsolete which presumably means that the 4.7 as a DP gun was obsolete. The comment you make about the 4in being lighter doesn't hold up, it was of course but it had a much higher rate of fire than would have made up the difference.

.

D) C'mon Coral Sea and Midway were 6 and 7 months into the war - about the same as the RN in Norway. The point is that the USN didn't find AA fire abovc 40degs to be very effective and the CO of Yorktown called for the vaunted 5in/38 to be removed entirely..

The issue isn't how long the UA had been at war. The issue is how much combat had the vessels seen. By the nature of georaphy the majority of the ships only fought when the navies sailed into combat at the large set piece combats. In Europe the RN was involved from day one, there was no phoney war for the RN.
Re your quote where does it say he wants the 5in removed, all I can see is a comment as to how good it is.

.

e) and at long ranges, 40deg elevation was just fine.
.

If fine means being close to defenceless against dive bombers and giving me about 40 seconds to engage and shoot down a level bomber with a gun that has a slow traverse and elevation rate plus an obsolte shell then we have a different definition of the word 'Fine'

 

[parsifal]

guys

its been a very good debate, and we have all had our chance to say our pieces. but the room has gone deathly quiet, and if we go any further with this, we will be crossing a line.

Time to move on.

 

[RCAFson]

Re your quote where does it say he wants the 5in removed, all I can see is a comment as to how good it is.

'

I just want to clarify this:

(e) Replacement of 5"38 caliber guns, 1.1" guns and 50 caliber machine guns, by a large number of 40mm automatic guns. While smaller caliber automatic guns have proven effective at short ranges, their range is too short to offer effective opposition to attacking planes prior to delivery of their attack. 5"38 caliber guns are very effective at long ranges and should be retained in ships which are used as anti-aircraft screening vessels.
Battle of Midway: USS Yorktown Action Report

The first sentence calls for the replacement of 5"/38, 1.1in and .5in guns with 40mm guns. So Yorktown's CO thought that the 5"/38 was less effective than 40mm fire.

In the same vein: "In theory, the 5in gun could counter either horizontal or torpedo bombers; it could not fire nearly fast enough to present any threat to dive bombers,which, ironically, were probably the most lethal threat to fast maneuverable craft such as destroyers." US Destroyers-An Illustrated Design History, Friedman, p203.

Finally, I've read somewhere where the RN did a study that showed that any engagement of an aircraft prior to bomb release would cause a drastic reduction in bombing accuracy - if this is the case then having some guns that can fire at very high angles might have a deterrent effect, if nothing else, but it seems to me that the same effect would be achieved with a 40mm bofors or pom-pom, and these guns would have a much higher probability of actually scoring a kill.

I guess that to prove anything, we would need to see some hard stats on WW2 naval AA.

 

[fastmongrel]

I think it would be fair to say that the best defence a Destroyer had was speed and manouverability. Destroyers with sea room were very hard to hit and a large number of those sunk were destroyers protecting slow moving vessels they could not leave to manouver independently or were close into shore.

 

[Glider]

I just want to clarify this:


The first sentence calls for the replacement of 5"/38, 1.1in and .5in guns with 40mm guns. So Yorktown's CO thought that the 5"/38 was less effective than 40mm fire.

In the same vein: "In theory, the 5in gun could counter either horizontal or torpedo bombers; it could not fire nearly fast enough to present any threat to dive bombers,which, ironically, were probably the most lethal threat to fast maneuverable craft such as destroyers." US Destroyers-An Illustrated Design History, Friedman, p203.

Finally, I've read somewhere where the RN did a study that showed that any engagement of an aircraft prior to bomb release would cause a drastic reduction in bombing accuracy - if this is the case then having some guns that can fire at very high angles might have a deterrent effect, if nothing else, but it seems to me that the same effect would be achieved with a 40mm bofors or pom-pom, and these guns would have a much higher probability of actually scoring a kill.

I guess that to prove anything, we would need to see some hard stats on WW2 naval AA.

I see where you are coming from on this. Unfortunately you didn't show all the requested chages.
The following listed alterations should be installed.

(a) A workable hand-powered ammunition supply for 5"38 caliber guns.
(b) A hand-operated cooling system, as an auxiliary, for the water-cooled automatic guns.
(c) Automatic fuse setters for 5"38 caliber guns not already so equipped.
(d) Automatic parallax control for 5"38 caliber fire control installations not already so equipped.
(e) Replacement of 5"38 caliber guns, 1.1" guns and 50 caliber machine guns, by a large number of 40mm automatic guns. While smaller caliber automatic guns have proven effective at short ranges, their range is too short to offer effective opposition to attacking planes prior to delivery of their attack. 5"38 caliber guns are very effective at long ranges and should be retained in ships which are used as anti-aircraft screening vessels.
(f) Replace a considerable percentage of the present 20mm explosive projectiles with A.P. projectiles. Observations in this and preceding actions indicate that the present 20mm projectiles seldom reach vital spots, and carry too small a charge to cause serious damage to surfaces against which they explode

The first four suggestions are to do with how to improve the 5in, the fifth a request for them to be removed whilst emphasising how good they were in anti aircraft screening vessels. Its almost as if they are saying please make these changes and until then replace them with 40mm. History shows that they made the changes and kept the 5in.

However this moves us away from the main topic, why did the RN take out 2 x 4.7 and replace them with 2 x 4in. According to your theory the Tribals didn't need to switch to anything as you see the 4.7 as a good DP gun. We know that the Tribal didn't have any weight issues as later in the war it accepted 6 x 40mm with no reduction in firepower.
So why would they want to add a twin 4in if it wasn't because the ships were lacking in AA fire

 

[RCAFson]

I see where you are coming from on this. Unfortunately you didn't show all the requested chages.
The following listed alterations should be installed.

(a) A workable hand-powered ammunition supply for 5"38 caliber guns.
(b) A hand-operated cooling system, as an auxiliary, for the water-cooled automatic guns.
(c) Automatic fuse setters for 5"38 caliber guns not already so equipped.
(d) Automatic parallax control for 5"38 caliber fire control installations not already so equipped.
(e) Replacement of 5"38 caliber guns, 1.1" guns and 50 caliber machine guns, by a large number of 40mm automatic guns. While smaller caliber automatic guns have proven effective at short ranges, their range is too short to offer effective opposition to attacking planes prior to delivery of their attack. 5"38 caliber guns are very effective at long ranges and should be retained in ships which are used as anti-aircraft screening vessels.
(f) Replace a considerable percentage of the present 20mm explosive projectiles with A.P. projectiles. Observations in this and preceding actions indicate that the present 20mm projectiles seldom reach vital spots, and carry too small a charge to cause serious damage to surfaces against which they explode

The first four suggestions are to do with how to improve the 5in, the fifth a request for them to be removed whilst emphasising how good they were in anti aircraft screening vessels. Its almost as if they are saying please make these changes and until then replace them with 40mm. History shows that they made the changes and kept the 5in.

However this moves us away from the main topic, why did the RN take out 2 x 4.7 and replace them with 2 x 4in. According to your theory the Tribals didn't need to switch to anything as you see the 4.7 as a good DP gun. We know that the Tribal didn't have any weight issues as later in the war it accepted 6 x 40mm with no reduction in firepower.
So why would they want to add a twin 4in if it wasn't because the ships were lacking in AA fire

The deficiencies of the 5in gun mounts were pointed out, but the key factor is that the report still recommends removing the 5in guns without qualification, rather than saying "if these changes are made the guns will be OK against dive bombers".

We've gone over the Tribal 4in gun situation several times. The only way to augument their HA firepower without unduly reducing surface firepower was to add a 4in twin mount. If the RN felt that the 4.7in was totally inadequate they had the option to replace all the guns with 4in and they didn't do that, except on the 4 of LM class because the 4.7in/50 was not available.

However, the fact remains that at least some captains in the USN felt that 5in guns were useless for short range AA fire, for example against divebombers - something that Friedman also states.

 

[RCAFson]

. I calculate that it will take 43 secs for the beam attack to get into firing posn, but firing time for the DD will be reduced to 26 secs after allowing for all of the above. At 10 rpm that means they will get off 4-5 rounds before launch.

For the equivalent 5/38, everything is the same, except time delay and rof. Because of the accelaration issue and higher traverse rate, the gun will be in firing position 9 secs after initial orders are given. That gives them 34secs of firing time, or 17 rounds at max rof.

So for a Tribal class with 8 x 4.7in we have 26sec x 8 guns = 34.7 shots
and for a JKM class, 26 sec x 6 guns = 26 shots
(assuming 10 RPM/gun)


A Benson or other 4 gun USN destroyer (typical prewar) we have 34 sec x 4 guns = 27 shots
(assuming 12RPM/Gun, the RoF according to Crenshaw of USS Maury )

later class with 4 guns = 34 rounds
(Later USN destroyers had a higher rate of fire, due to a superior fuze setter arrangement and had a RoF of 15RPM/gun)

The RN destroyers will also be able to engage the aircraft with their quad pom-pom. Overall I don't see a huge advantage for the USN destroyers, and if we include the pom-pom, I'd say they were at a disadvantage, because their CIWS = 4 x .5in HMGs.

The other factor is the time for the AA FC computer to generate a solution. Crenshaw says it took about 30 seconds for the Mk 33 computer. My understanding is that the FKC could come to solution very quickly and RN picked FKC and HACS to avoid the slow solution speeds of tachymetric computers as used on USN destroyers.

 

[parsifal]

So for a Tribal class with 8 x 4.7in we have 26sec x 8 guns = 34.7 shots
and for a JKM class, 26 sec x 6 guns = 26 shots
(assuming 10 RPM/gun)


A Benson or other 4 gun USN destroyer (typical prewar) we have 34 sec x 4 guns = 27 shots
(assuming 12RPM/Gun, the RoF according to Crenshaw of USS Maury )

later class with 4 guns = 34 rounds
(Later USN destroyers had a higher rate of fire, due to a superior fuze setter arrangement and had a RoF of 15RPM/gun)

Its not a fair comparison. you are comparing the theoretical rof of the british DDs with the practical rof for the bensons. The two terms are not interchaneable. The practical rof for the 4.7in was around 4-8 rpm. On that basis the Tribals will get off around 13-14 rounds (from an 8 gun broadside) , whilst the JKN will be propportionally smaller. If you want to compare theoretical maximums, you need to do so for all classes, In that case the rofs are 10rpm for the 4.7 and 24 rpm for the 5/38, which we could arbitarily taken as 20rpm, simply because some sources say its 20rpm. On that basis, the Bensons will get off 54 rounds in the same time as the 13 rounds are fired by by the tribals and about 10 for the JKNs. There is simply no comparison in the ROFs.

Ive served on ships that have the 4.5in as main armament, and observed fire onboard Gearing class DDs. I can assure you there is no comparison when it comes to Practical rofs. I will concede that in reality the theoretical rofs are not a true reflection of actual practical rofs. the po st war 5/54 with auto loader has a theoretical rof of nearly 60 rpm, but in reality could only sustain about 20 rpm. Hand loaded mounts will never do well when it comes to actual sustained rof, and rammed breeches are even worse when the mount is operating in the AA role.

This is moreso the case for the 4.7 guns, which still required ramming of each round. at elevation the workable rate of fire would have dropped right away, as crews struggled to get each round rammed home and in the chamber. Trying to argue that the British DDs had a comparable ROF to the bensons in an AA role is a complete dud Im afraid.

The RN destroyers will also be able to engage the aircraft with their quad pom-pom. Overall I don't see a huge

advantage for the USN destroyers, and if we include the pom-pom, I'd say they were at a disadvantage, because their CIWS = 4 x .5in HMGs.

Only the 2pdrs can provide any real fire against torpedo bombers, and that is a theoretical capability, not a real one. 20mm weapons and MGs were almost totally impotent against torps fired at normal ranges because they lacked sufficient effective range. They were effective at making torps keep their distance, that i will grant you.

The 2 pdr was judged an advanced weapon when introduced, but by the outbreak of World War II advances in aircraft would have made it obsolete but for the introduction of a high-velocity round and new director designs (which were not available at the beginning of the war for DDs) . It was intended that the curtain of fire it threw up would be sufficient to deter attacking aircraft, which it could sometimes achieve, but its performance was hampered by the ineffective Mk III director.The MK IV Director with a Gyro Rate Unit and Type 282 radar was an improvement and was introduced on the King George V-class battleships, but not in DDs until much later.

In January 1941, HMS Illustrious′s Mk VIII mountings performed flawlessly firing 30,000 rounds with very few stoppages (accounting for 2 known kills). When HMS Prince of Wales was attacked and sunk by Japanese aircraft near Singapore, the subsequent RN report judged that a single 40 mm Bofors gun firing tracer was a more effective anti-aircraft weapon than a full eight barrelled pom pom. The Bofors had better range (about double in terms of effective range) and could deliver far more accurate fire, compared to a multiple pom-pom in director control, as the pom-poms did not have tracer ammunition, and the weapon lacked effective range. In the PoWs case, moreover, the pom-pom ammunition had deteriorated badly in their ready use lockers, while the Type 282 radar units also failed in the equatorial heat. In the same action, the Commissioned Gunner of HMS Repulse spent the whole action running from one pom-pom mount to another trying to keep them operational due to the faulty ammunition. The pom-poms on Repulse shot down two of the four confirmed kills made by Force Z, while Prince of Wales′ pom-poms did record hits on enemy aircraft but no kills (the other 2 of the total 4 losses were not lost to british action) . 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. This was because Kamikazes had to penetrate to within the kill zone of the weapon more than anything

So no, against a torpedo bomber operating at normal range, I would say the CIWs aboard the British ships would make hardlky any difference. They made some difference to Divebombers and Suicide aircraft, but if a D/B or Kamikaze is that close, as to allow the pom poms to be effective, the Pom Pom has failed in its primary deterrent role anyway. 30000 rounds to shoot down 2 aircraft is not a great result, and not evidence of an effective weapon. Compare that to the 14-26 confirmed kills (depending on who you read) from the South Dakota a year or so later at Santa Cruz, and you start to get some idea of the different efficieny levels of the two weapon systems.

The other factor is the time for the AA FC computer to generate a solution. Crenshaw says it took about 30 seconds for the Mk 33 computer. My understanding is that the FKC could come to solution very quickly and RN picked FKC and HACS to avoid the slow solution speeds of tachymetric computers as used on USN destroyers.

Thats completely at odds with both campbell and Nav Weapons. this will get down to who you want to believe.....I choose to believe Campbell and Nav weapons. And operational results that we do have, whilst pretty sparse, dont support the claims you make in this regard.

 

[RCAFson]

Its not a fair comparison. you are comparing the theoretical rof of the british DDs with the practical rof for the bensons. The two terms are not interchaneable. The practical rof for the 4.7in was around 4-8 rpm. On that basis the Tribals will get off around 13-14 rounds (from an 8 gun broadside) , whilst the JKN will be propportionally smaller. If you want to compare theoretical maximums, you need to do so for all classes, In that case the rofs are 10rpm for the 4.7 and 24 rpm for the 5/38, which we could arbitarily taken as 20rpm, simply because some sources say its 20rpm. On that basis, the Bensons will get off 54 rounds in the same time as the 13 rounds are fired by by the tribals and about 10 for the JKNs. There is simply no comparison in the ROFs.

Ive served on ships that have the 4.5in as main armament, and observed fire onboard Gearing class DDs. I can assure you there is no comparison when it comes to Practical rofs. I will concede that in reality the theoretical rofs are not a true reflection of actual practical rofs. the po st war 5/54 with auto loader has a theoretical rof of nearly 60 rpm, but in reality could only sustain about 20 rpm. Hand loaded mounts will never do well when it comes to actual sustained rof, and rammed breeches are even worse when the mount is operating in the AA role.

This is moreso the case for the 4.7 guns, which still required ramming of each round. at elevation the workable rate of fire would have dropped right away, as crews struggled to get each round rammed home and in the chamber. Trying to argue that the British DDs had a comparable ROF to the bensons in an AA role is a complete dud Im afraid.




Only the 2pdrs can provide any real fire against torpedo bombers, and that is a theoretical capability, not a real one. 20mm weapons and MGs were almost totally impotent against torps fired at normal ranges because they lacked sufficient effective range. They were effective at making torps keep their distance, that i will grant you.

The 2 pdr was judged an advanced weapon when introduced, but by the outbreak of World War II advances in aircraft would have made it obsolete but for the introduction of a high-velocity round and new director designs (which were not available at the beginning of the war for DDs) . It was intended that the curtain of fire it threw up would be sufficient to deter attacking aircraft, which it could sometimes achieve, but its performance was hampered by the ineffective Mk III director.The MK IV Director with a Gyro Rate Unit and Type 282 radar was an improvement and was introduced on the King George V-class battleships, but not in DDs until much later.

In January 1941, HMS Illustrious′s Mk VIII mountings performed flawlessly firing 30,000 rounds with very few stoppages (accounting for 2 known kills). When HMS Prince of Wales was attacked and sunk by Japanese aircraft near Singapore, the subsequent RN report judged that a single 40 mm Bofors gun firing tracer was a more effective anti-aircraft weapon than a full eight barrelled pom pom. The Bofors had better range (about double in terms of effective range) and could deliver far more accurate fire, compared to a multiple pom-pom in director control, as the pom-poms did not have tracer ammunition, and the weapon lacked effective range. In the PoWs case, moreover, the pom-pom ammunition had deteriorated badly in their ready use lockers, while the Type 282 radar units also failed in the equatorial heat. In the same action, the Commissioned Gunner of HMS Repulse spent the whole action running from one pom-pom mount to another trying to keep them operational due to the faulty ammunition. The pom-poms on Repulse shot down two of the four confirmed kills made by Force Z, while Prince of Wales′ pom-poms did record hits on enemy aircraft but no kills (the other 2 of the total 4 losses were not lost to british action) . 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. This was because Kamikazes had to penetrate to within the kill zone of the weapon more than anything

So no, against a torpedo bomber operating at normal range, I would say the CIWs aboard the British ships would make hardlky any difference. They made some difference to Divebombers and Suicide aircraft, but if a D/B or Kamikaze is that close, as to allow the pom poms to be effective, the Pom Pom has failed in its primary deterrent role anyway. 30000 rounds to shoot down 2 aircraft is not a great result, and not evidence of an effective weapon. Compare that to the 14-26 confirmed kills (depending on who you read) from the South Dakota a year or so later at Santa Cruz, and you start to get some idea of the different efficieny levels of the two weapon systems.



Thats completely at odds with both campbell and Nav Weapons. this will get down to who you want to believe.....I choose to believe Campbell and Nav weapons. And operational results that we do have, whilst pretty sparse, dont support the claims you make in this regard.

Where do you get 4-8 rpm for a 4.7in twin? The twin had power ramming, BTW, and in trials even the single could achieve close to 18 RPM:
During gunnery trials in 1930, HMS Basilisk'' was able to fire "...five rounds in 17 seconds."
, Kimberly at Narvik: "Salvos fired about 180 in all...drill to guns very good, great part of the action a loading interval of about 5 seconds was achieved..."
4.7 inch QF Mark IX XII - Wikipedia, the free encyclopedia but both above extracts are quotes from British Destroyers, by F. March.

Campbell states a 5 sec firing cycle for the 4.7in twin and Navweaps states: CPXIX (twin) Mounting: 10 - 12 rounds per minute , and I can't see where they state otherwise.
Navweaps states, for the 5"/38:
Pedestal and other mounts lacking integral hoists: 12 - 15 rounds per minute (mark 33 destroyers)
Base ring mounts with integral hoists: 15 - 22 rounds per minute (later mark 37 destroyers)

I think you need to provide some sources for your assertions, regarding 4.7in RoF. There are many sources that state 10-12 rpm including RN action reports. The first RN 4.5 destroyer twin was not comparable to the 4.7in twin which was a completely different mount. Campbell also states that Illustrious fired 3000 rounds of 4.5in ammo at an average of 12 rounds per gun per minutes during Operation Excess, and her 4.5in twins had a very similar loading system to the 4.7in twin. The pom-pom and 4.5in ammo fired by Illustrious was fired during the entire action including her stay at Malta.

According to Lundstrom the USN made 25 AA kills shared amongst all the USN ships at Santa Cruz (The USN claimed 127 kills at Santa Cruz!).

In any event, I was comparing the RN and USN destroyers in their original format, not after years of war mods. So the original outfit of the RN destroyers was quad pom-poms and quad .5in mounts versus 4 x .5in MGs for the USN destroyers. Your scenario implied that the aircraft would have to pass close to the destroyer, and if so they would come within pom-pom fire.

Finally, you have to remember that post war AA firing were typically using VT ammo, so they could skip the MT fuzesetter, which sped things up.

 

[tomo pauk]

One can read many interesting things here. Thanks, people.

 

[Juha]

The deficiencies of the 5in gun mounts were pointed out, but the key factor is that the report still recommends removing the 5in guns without qualification, rather than saying "if these changes are made the guns will be OK against dive bombers".

We've gone over the Tribal 4in gun situation several times. The only way to augument their HA firepower without unduly reducing surface firepower was to add a 4in twin mount. If the RN felt that the 4.7in was totally inadequate they had the option to replace all the guns with 4in and they didn't do that, except on the 4 of LM class because the 4.7in/50 was not available.

However, the fact remains that at least some captains in the USN felt that 5in guns were useless for short range AA fire, for example against divebombers - something that Friedman also states.

For RN 4" gun wasn't a realistic option, because it lacked enough punch for being an adequate surface gun. But it was adequate HA gun. And it was fairly common in the early war emergency DDs. So of 16 O- P-classes DDs only 4 had 4.7" guns and 12 had 4" guns. But as the duel of Petard and Paladin vs IJN I-27 showed, against surface targets 4" was totally inadequate, its SAP round was unable to penetrate pressure hull of I-27.

Juha

 

[vinnye]

The problem with armament is complex and has a lot to do with the role that it is anticipated to do most often.
So a fleet destroyer that was expected to engage enemy destroyers is most likely to have a larger calibre gun eg 4.7 or 5 inch.
But as often happens - the destroyers were called upon to undertake many roles - sometimes acting independent of other units and being exposed to aerial attack. This showed up a deficiency in AA capability - which was not anticipated during the design stage. Hence modifications were carried out to improve AA capability - this often meant HA guns of smaller calibres eg 4 inch. So a compromise is often arrived at that involves a mixture of calibres that enable the ship to have some hope of succes in different roles.

 

[parsifal]

Where do you get 4-8 rpm for a 4.7in twin? The twin had power ramming, BTW, and in trials even the single could achieve close to 18 RPM:
During gunnery trials in 1930, HMS Basilisk'' was able to fire "...five rounds in 17 seconds."
, Kimberly at Narvik: "Salvos fired about 180 in all...drill to guns very good, great part of the action a loading interval of about 5 seconds was achieved..."
4.7 inch QF Mark IX XII - Wikipedia, the free encyclopedia but both above extracts are quotes from British Destroyers, by F. March.

These are max rates of fire. Practical rates of fire are a lot less than maximums. Usually about half the rate by rule of thumb. Ive got a source somewhere. i wil look it up and post it soon.

Campbell states a 5 sec firing cycle for the 4.7in twin and Navweaps states: CPXIX (twin) Mounting: 10 - 12 rounds per minute , and I can't see where they state otherwise.

These are max rates, not practical rates. they are different.

Navweaps states, for the 5"/38:
Pedestal and other mounts lacking integral hoists: 12 - 15 rounds per minute (mark 33 destroyers)
Base ring mounts with integral hoists: 15 - 22 rounds per minute (later mark 37 destroyers)

Glad that you mentioned Nvweapons, because i the bit you are drawing from it states in full regarding all marks of the 4.7 in weapon

"The lack of a DP function for these weapons was keenly felt throughout the war as more British destroyers were sunk by air attack than from any other cause. What little AA capability that these weapons did have was hindered by a lack of a tachymetric (predictive) fire control system and the setting of HE time fuzes by hand. The last single mounting designed, the CPXXII, had a spring operated rammer, but all other single mountings were completely hand worked. The twin mounting had power ramming and used power training and elevation but no RPC gear was installed".

With regard to the Bensons, they were not equipped with 4 x 5/38s at thge beginning of the war, they were armed with 5x 5/38s. by the time they landed the 5th 5/38, they were authorised (and generally did carry) 4x 40mm and 8 x 20mm AA weapons.

Moreover, the Bensons used the mk30 mount,, which was not a pedestal mount. You are misquoting or selectively quoting Navweappons here. Relevantly it states.

The Mark 30 mountings made up by far the majority of single mountings built during the war. The Mark 30 enclosed base ring mounts were first introduced on USS Wichita (CA-45). The Mark 30 ran up to Mod 86, with Mod 0 being the original enclosed mounting and Mod 1 being the original open mounting. There were also semi-enclosed mounts which had the upper half of the shield removed as a weight savings but having a canvas cover to protect the interior of the mount. Many of the Mark 30 modifications were trivial in nature. For example, USS Fletcher (DD-445) used Mod 16 in positions 1 and 5, Mod 19 in position 2, Mod 30 in position 3 and Mod 31 in position 4. The differences were mainly related to the elevation and training limitations inherent in the different mounting positions. Escort Carriers (CVE) completed during the war used Mark 30 Mod 80 which was a simplified base ring mounting which lacked shields, axial hoists and RPC. The maximum elevation of this Mod was restricted to +27 degrees as it was installed under the flight deck overhang. The single open Mark 30 Mod 48 and Mark 30 Mod 51 mountings were simplified base-ring types for auxiliaries and merchant ships and lacked integral shell hoists. Trunnion height was 58.0 inches (147 cm) above the loading platform. 55 inches (140 cm) is considered the maximum desirable trunnion height when firing at low elevations for a 50 - 55 lbs. (22.7 - 24.9 kg) projectile.

Almost all Mark 25 and Mark 30 base ring single mounts had an integral shell hoist on the axis of the mounting which allowed shells to be passed directly to the gun at any angle of train. Fuzes were automatically set as the shells traveled up the hoist. Cartridges were passed up to the gun through a scuttle also on the rotating mass. These base ring mounts with integral shell hoists and cartridge scuttles had the advantage that projectiles and cartridges were presented to the loaders at exactly the same position and orientation regardless of the mount's elevation or training and thus simplified and sped up the loading procedure. Both the shell hoist and the cartridge scuttle were on the left side of the mount. Mark 25 and enclosed Mark 30 base ring mountings used a single 10 hp motor to work both elevation and train, a 7.5 hp motor for the hoists and a 7.5 hp or 5 hp motor for ramming.

8) All twin SP and DP mounts were base ring types and were generally similar to single enclosed base ring mounts. Twin mounts differed from single mounts in that there were twin powder hoists for the cartridges on the rotating structure as well as twin shell hoists. The hoists for the right gun came up through the deck on the left side of the gun while those for the left gun came up on the right side of the gun. Twin mounts took about 27 crewmen in the mount itself and in the upper handling room. Additional personnel were required in the lower handling room during sustained firing periods.

All twin DP mountings were equipped with RPC gear and powered by electric motors through hydraulic gear. Training was by a 4 hp motor while the guns were elevated by a 7.5 or 10 hp motor. Each gun had a 7.5 or 10 hp motor for the hoists and a 5 or 7 hp motor for the rammer.

So, in comparison to the 4.7 in gun which does not have rpc in the Mk XII mount and had a fussy loading system, and poor turret layouts and design, we have An American system that is designed for the purpose, and stated as the best of its kind in the world at that time.

I think you need to provide some sources for your assertions, regarding 4.7in RoF.

Agreed, but it would be a great start if I could get you to understand the difference between Max rof and practical rof.

In any event, I was comparing the RN and USN destroyers in their original format, not after years of war mods. So the original outfit of the RN destroyers was quad pom-poms and quad .5in mounts versus 4 x .5in MGs for the USN destroyers.

You were actually kind of allover the place really. You were comparing the Bensons....a Destroyer class that did not start to commission until late 1940-41, but were quoting the main armament after modification and reduction. You were comparing the prewar light AA compopnent which the Americans began to rectify in the first months of their entry .

And you selectively or outright misquote Navweapons which makes very clear that the 4.7 gun was an inadequate AA weapon, and also very clearly states the 5/38 was the best DP weapon during the war.

Finally, you have to remember that post war AA firing were typically using VT ammo, so they could skip the MT fuzesetter, which sped things up

.

True, but in the age of time fuzed shells, the US arrangements according to Navweapons were far more efficient compared to the 4.7 mounts.

 

[RCAFson]

These are max rates of fire. Practical rates of fire are a lot less than maximums. Usually about half the rate by rule of thumb. Ive got a source somewhere. i wil look it up and post it soon.



These are max rates, not practical rates. they are different.



Glad that you mentioned Nvweapons, because i the bit you are drawing from it states in full regarding all marks of the 4.7 in weapon

"The lack of a DP function for these weapons was keenly felt throughout the war as more British destroyers were sunk by air attack than from any other cause. What little AA capability that these weapons did have was hindered by a lack of a tachymetric (predictive) fire control system and the setting of HE time fuzes by hand. The last single mounting designed, the CPXXII, had a spring operated rammer, but all other single mountings were completely hand worked. The twin mounting had power ramming and used power training and elevation but no RPC gear was installed".

With regard to the Bensons, they were not equipped with 4 x 5/38s at thge beginning of the war, they were armed with 5x 5/38s. by the time they landed the 5th 5/38, they were authorised (and generally did carry) 4x 40mm and 8 x 20mm AA weapons.

Moreover, the Bensons used the mk30 mount,, which was not a pedestal mount. You are misquoting or selectively quoting Navweappons here. Relevantly it states.

The Mark 30 mountings made up by far the majority of single mountings built during the war. The Mark 30 enclosed base ring mounts were first introduced on USS Wichita (CA-45). The Mark 30 ran up to Mod 86, with Mod 0 being the original enclosed mounting and Mod 1 being the original open mounting. There were also semi-enclosed mounts which had the upper half of the shield removed as a weight savings but having a canvas cover to protect the interior of the mount. Many of the Mark 30 modifications were trivial in nature. For example, USS Fletcher (DD-445) used Mod 16 in positions 1 and 5, Mod 19 in position 2, Mod 30 in position 3 and Mod 31 in position 4. The differences were mainly related to the elevation and training limitations inherent in the different mounting positions. Escort Carriers (CVE) completed during the war used Mark 30 Mod 80 which was a simplified base ring mounting which lacked shields, axial hoists and RPC. The maximum elevation of this Mod was restricted to +27 degrees as it was installed under the flight deck overhang. The single open Mark 30 Mod 48 and Mark 30 Mod 51 mountings were simplified base-ring types for auxiliaries and merchant ships and lacked integral shell hoists. Trunnion height was 58.0 inches (147 cm) above the loading platform. 55 inches (140 cm) is considered the maximum desirable trunnion height when firing at low elevations for a 50 - 55 lbs. (22.7 - 24.9 kg) projectile.

Almost all Mark 25 and Mark 30 base ring single mounts had an integral shell hoist on the axis of the mounting which allowed shells to be passed directly to the gun at any angle of train. Fuzes were automatically set as the shells traveled up the hoist. Cartridges were passed up to the gun through a scuttle also on the rotating mass. These base ring mounts with integral shell hoists and cartridge scuttles had the advantage that projectiles and cartridges were presented to the loaders at exactly the same position and orientation regardless of the mount's elevation or training and thus simplified and sped up the loading procedure. Both the shell hoist and the cartridge scuttle were on the left side of the mount. Mark 25 and enclosed Mark 30 base ring mountings used a single 10 hp motor to work both elevation and train, a 7.5 hp motor for the hoists and a 7.5 hp or 5 hp motor for ramming.

8) All twin SP and DP mounts were base ring types and were generally similar to single enclosed base ring mounts. Twin mounts differed from single mounts in that there were twin powder hoists for the cartridges on the rotating structure as well as twin shell hoists. The hoists for the right gun came up through the deck on the left side of the gun while those for the left gun came up on the right side of the gun. Twin mounts took about 27 crewmen in the mount itself and in the upper handling room. Additional personnel were required in the lower handling room during sustained firing periods.

All twin DP mountings were equipped with RPC gear and powered by electric motors through hydraulic gear. Training was by a 4 hp motor while the guns were elevated by a 7.5 or 10 hp motor. Each gun had a 7.5 or 10 hp motor for the hoists and a 5 or 7 hp motor for the rammer.

So, in comparison to the 4.7 in gun which does not have rpc in the Mk XII mount and had a fussy loading system, and poor turret layouts and design, we have An American system that is designed for the purpose, and stated as the best of its kind in the world at that time.



Agreed, but it would be a great start if I could get you to understand the difference between Max rof and practical rof.




You were actually kind of allover the place really. You were comparing the Bensons....a Destroyer class that did not start to commission until late 1940-41, but were quoting the main armament after modification and reduction. You were comparing the prewar light AA compopnent which the Americans began to rectify in the first months of their entry .

And you selectively or outright misquote Navweapons which makes very clear that the 4.7 gun was an inadequate AA weapon, and also very clearly states the 5/38 was the best DP weapon during the war.

.

True, but in the age of time fuzed shells, the US arrangements according to Navweapons were far more efficient compared to the 4.7 mounts.

Why would navweaps and Campbell state max rates for RN guns and practical rates for USN guns - that makes no sense at all! Yet you want to hold Navweaps up as gospel. I am willing to agree with their data but not their editorial comments which are not based upon any scientific basis, except simple hearsay.
The data from Navweaps and Wikipedia from Illustrious and HMS Kimberly's action reports showing a 5 sec loading cycle or from Basilysk showing 5 rounds in 17 seconds shows us that average RoF in combat was ~12 rpm.

We are talking about the twin mountings as used in the Tribal or JKMN classes, the earlier classes didn't have AA FC and wartime pressures prevented it from being universally retrofitted, and the first wartime fleet destroyers (O-P-Q-R classes) had to continue with the weapons that were in storage or easily produced as wartime Britain didn't have the capacity to introduce more modern designs quickly during the war.

The Benson class had Mk 37 and integral hoists, but the 1939 and earlier classes did not, but these were the last USN destroyers built to treaty limits, whereas the UK, because of wartime pressures, had to continue building destroyers with treaty based hulls until the Battle class of 1945.

All these repeat ships were ordered with only four 5-inch/38s due to severe topweight problems with the initial ships. Thus differentiated, they were launched as the Bristol (DD 453) class and, less the lead ship (already attached to DesRon 13) and Barton, were organized into Destroyer Squadrons 10, 12, and 14–19. This distinction also disappeared, however, when the first 24 Bensons and Gleaves were modified to match as follows (see also ARMAMENT):
Ships in DesRon 11 (DesDiv 21, which remained in the Atlantic, and DesDiv 22, the first ships of the class deployed to the Pacific)—and DesRon 13 retained ten torpedo tubes but landed their No. 3 5-inch mount, while increasing their .50 cal armament to twelve guns.
Ships assigned to DesRon 7 landed their after torpedo tube mounts and added four .50 cal machine guns.
« « «
Twenty-seven Bensons and Gleaves were in commission at the start of World War II [Dec 7 1941]—then the US Navy's most modern destroyers. Except for temporary assignment by Fletchers (e.g., at the North Africa landings in 1942) and Allen M. Sumners (e.g., at Normandy), they remained the US Navy's workhorse destroyers in the Atlantic and Mediterranean theaters.
Benson-Gleaves Class Home Page

(I added the info in square brackets)

No Benson class ships were in commission in April or May 1940 and only one by June 1940.
The First Sumner class (twin 5"/38 ) didn't enter service until 1944 - only 3 twin mount 5"/38 gunned DDs in commission by Jan 1944)

The RN entered the war with it's pre-war main armament and CIWS; what would have happened if the USN did the same? How would USN destroyers have fared in Norway or at Dunkirk!

The problem is that instead of thinking for yourself, you seem to want to simply repeat Navweaps editorial comments - this makes for a pretty poor discussion, when as, I've stated, repeatedly, that I don't agree with their editorial comments. And you also dispute Navweaps data by asking us to pretend that RN RoFs were only half of what they state.