British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

[Steve Crandell]

I'm somewhat confused. You said "PoW did quite well against level bombers at ~9000ft (IIRC) using radar, even with a substantial list and half her 5.25in armament OOCS". I'm not sure you addressed my question, which was whether a US ship could do as well PoW could do. If not, why not? You did say PoW was getting radar ranges, which was something US ships didn't have for quite some time. Of course even with radar ranges you can only fire accurately against level bombers, so maybe not worth it generally speaking. Against late war Kamikazes Mark 51 didn't use radar.

I believe I've read that most of the IJN aircraft shot down in the Pearl Harbor attack were victims of .50 MGs. Not too surprising since the FC organization of a lot of the ships wasn't functioning. What is surprising is how many were shot down, actually.

[dunmunro]

I think the salient points are that there was over 100 observed runs and only a few drones (6 IIRC) were shot down. There probably was a tendency to overestimate the potential kill rate of service ammo vs actual targets, especially given the low speed (~100 knots) of the Queen Bee drone and the relatively low altitude (~8000ft). OTOH, if we add radar ranging, improved HACS, and VT ammo we should see a pretty good kill rate, against a TD2C drone at 130-150 knots. PoW did quite well against level bombers at ~9000ft (IIRC) using radar, even with a substantial list and half her 5.25in armament OOS.

As I understand this post, you believe that it is actually possible for shipborne HAA to shoot down aircraft, as long as they approach in a formation on a predictable course and speed. That makes sense. Do you think a US ship might also be able to do this with Mark 37?

Unfortunately the IJN usually didn't use level bombing against naval targets, with the attack on anchored ships in Pearl Harbor a notable exception.

Naval HAA can always hit targets but whether they can achieve a high enough kill rate to be effective is the issue. The kill rate against manoeuvring targets will always be very low with MT ammo. VT changes the equation considerably and potentially so does zero deadtime MT fire as with the RN ABU.

I've studied 3 examples of USN TFs against IJN level bomber formations at Bougainville, Coral Sea (Crace's RAN/USN cruisers and USN destroyers) and at Coral Sea (a formation of B5N's level bombed, and hit Hornet) and the results were all pretty dismal, AFAICT, and on the face of it no better than similar RN AA encounters in 1940/41 in the Mediterranean.

[wmh829386]

You are quoting AFCC manual, but the data flow diagram from Tribals shows the FKC directly generate gun elevation order, bypassing AFCC. There is no wind input at the FKC so elevation is not corrected. You might want to check it again.
https://www.kbismarck.org/forum/downloa ... hp?id=3921

There's three inputs:

Gun deflection = wind input
Gun elevation
Gun range = Wind input. Gun range is a modifier to gun elevation.

No, you are misinterpreting the diagram. The Gun range is supplied to the LA local gun sight only, it works with the gun Deflection allowimg gun to be fired when FTP/RPC is not used.
Normally the local gun sight is not used!

In normal HA operation, the FKC supply gun elevation to gun elevation unit directly, and gun train comes from AFCC.

[wmh829386]

To be fair, drones comming back riddled would indicate shell design issue more so than FC design.

Just an anecdote: In WW1, heavy black power common shell was found to produce much larger fragments than Lyddite filled shell, hence much more effective...

.50 cal fragments is going to have less penetration than .50 cal bullets. It's natural to not fair well to modern full metal bombers...
There is a potential for deep deep irony if the reduces load black power practice shell creates larger fragments.

[dunmunro]

I'm somewhat confused. You said "PoW did quite well against level bombers at ~9000ft (IIRC) using radar, even with a substantial list and half her 5.25in armament OOCS". I'm not sure you addressed my question, which was whether a US ship could do as well PoW could do. If not, why not? You did say PoW was getting radar ranges, which was something US ships didn't have for quite some time. Of course even with radar ranges you can only fire accurately against level bombers, so maybe not worth it generally speaking. Against late war Kamikazes Mark 51 didn't use radar.

I believe I've read that most of the IJN aircraft shot down in the Pearl Harbor attack were victims of .50 MGs. Not too surprising since the FC organization of a lot of the ships wasn't functioning. What is surprising is how many were shot down, actually.

PoW's HAA stands out. It was accurate according to the IJN, and effective. Part of the reason is that the 5.25in gun had excellent ballistics and fired a very heavy shell, but her AA FC had to be good as well, and she repeated the performance in two separate formation attacks. The HADT4GB would be able to provide some measure of close range accuracy when using VT ammo via GRU/GRUB, however even using an eyeshooting sight as the HADT GO's sight or the slew sight on Mk37 should give reasonable kill probabilities when using VT ammo against directly approaching close range targets. Late war KGV was able to accurately engage low level IJN TE bombers, according to her gunnery report, using MT ammo and type 285P radar due to advances in HACS low angle FC.

Mk51 and 5in/38 could only engage close range targets and then only when using VT ammo, as it had no provision for controlling MT fuze setting. The Mk52 and Mk57 (IIRC) directors were similar but added radar ranging.

The USN actually expended about 10 thousand rounds of 3in and 5in ammo at Pearl Harbour but also ~14 thousand of rounds of 1.1in, ~300k rounds of .5in and 47K round of .3in, according the BuOrd's AA Summary.

[wmh829386]

however even using an eyeshooting sight as the HADT GO's sight or the slew sight on Mk37 should give reasonable kill probabilities when using VT ammo against directly approaching close range targets.

Consider that the Mk51 lost half its effectiveness using fixed range setting, even against directly approaching target, I think you are too optimistic.

[dunmunro]

however even using an eyeshooting sight as the HADT GO's sight or the slew sight on Mk37 should give reasonable kill probabilities when using VT ammo against directly approaching close range targets.

Consider that the Mk51 lost half its effectiveness using fixed range setting, even against directly approaching target, I think you are too optimistic.

MK51 used a disturbed line of sight so this is to be expected, but even 1/2 the accuracy still gives a good probability of a TTB. You can look this up in the anti-suicide summaries posted earlier.

[dunmunro]

To be fair, drones comming back riddled would indicate shell design issue more so than FC design.

Just an anecdote: In WW1, heavy black power common shell was found to produce much larger fragments than Lyddite filled shell, hence much more effective...

.50 cal fragments is going to have less penetration than .50 cal bullets. It's natural to not fair well to modern full metal bombers...
There is a potential for deep deep irony if the reduces load black power practice shell creates larger fragments.

The RN called it 'innocuous' shell for a reason. It was designed to minimize kill potential and maximize visibility and the charge was only large enough for that purpose.

Drones were not coming back riddled and the 5% figure included drones where the potential pilot was judged to have been incapacitated.

[dunmunro]

You are quoting AFCC manual, but the data flow diagram from Tribals shows the FKC directly generate gun elevation order, bypassing AFCC. There is no wind input at the FKC so elevation is not corrected. You might want to check it again.
https://www.kbismarck.org/forum/downloa ... hp?id=3921

There's three inputs:

Gun deflection = wind input
Gun elevation
Gun range = Wind input. Gun range is a modifier to gun elevation.

No, you are misinterpreting the diagram. The Gun range is supplied to the LA local gun sight only, it works with the gun Deflection allowimg gun to be fired when FTP/RPC is not used.
Normally the local gun sight is not used!

In normal HA operation, the FKC supply gun elevation to gun elevation unit directly, and gun train comes from AFCC.

From the Gunnery Pocket Book:

iii) As the shell takes some time to travel (called "Time of Flight") the enemy will have moved closer or farther away from our own ship by the time the shell has arrived. This distance has to be allowed for on top of our Clock Range. Our own speed, especially if firing right ahead, will affect the speed of the shell as also will the wind, the effect being greatest, so far as the range is concerned, if firing straight into the wind or with the wind blowing directly behind the shell. This will affect the distance the shell will travel, and so will the shape of the shell, and the temperature and the density of the air, especially if they differ much from the normal that is used in the design of the calculating instrument.

All the above are known collectively as the RANGE CORRECTION, and it has to be added to or subtracted from the Clock Range, to get the most accurate range to go to the gun, called the GUN RANGE. This Gun Range must now be converted into an angle of elevation and goes to the electrical pointers in the Elevation Receivers at the guns, which it will be remembered from the previous discussion on Director Firing (see para. 276) are already being moved by the Director Layer to counteract the roll of the ship.
Thus the final GUN ELEVATION is the correct elevation above the horizontal plane for that gun range.

[wmh829386]

There's three inputs:

Gun deflection = wind input
Gun elevation
Gun range = Wind input. Gun range is a modifier to gun elevation.

No, you are misinterpreting the diagram. The Gun range is supplied to the LA local gun sight only, it works with the gun Deflection allowimg gun to be fired when FTP/RPC is not used.
Normally the local gun sight is not used!

In normal HA operation, the FKC supply gun elevation to gun elevation unit directly, and gun train comes from AFCC.

From the Gunnery Pocket Book:

iii) As the shell takes some time to travel (called "Time of Flight") the enemy will have moved closer or farther away from our own ship by the time the shell has arrived. This distance has to be allowed for on top of our Clock Range. Our own speed, especially if firing right ahead, will affect the speed of the shell as also will the wind, the effect being greatest, so far as the range is concerned, if firing straight into the wind or with the wind blowing directly behind the shell. This will affect the distance the shell will travel, and so will the shape of the shell, and the temperature and the density of the air, especially if they differ much from the normal that is used in the design of the calculating instrument.

All the above are known collectively as the RANGE CORRECTION, and it has to be added to or subtracted from the Clock Range, to get the most accurate range to go to the gun, called the GUN RANGE. This Gun Range must now be converted into an angle of elevation and goes to the electrical pointers in the Elevation Receivers at the guns, which it will be remembered from the previous discussion on Director Firing (see para. 276) are already being moved by the Director Layer to counteract the roll of the ship.
Thus the final GUN ELEVATION is the correct elevation above the horizontal plane for that gun range.

I know very clearly what those terms mean. I will explain this one more time. It is up to you to accept it or not.

According to the Tribal's FC diagram you supplied (thank you, it's great), FKC generates HA GUN ELEVATION directly, but it does not take wind correction itself.

When the FC is switched to HA, the HA GUN ELEVATION goes through the switch and straight into gun elevation unit then to the layers' FtP receiver. Please check the diagram to confirm this.

FKC does not have a spotting correction input anywhere!
Please check the diagram to confirm this.

Height is implied (never showed up on diagram) by corrected sight elevation and slant range, no manual adjustment of height for spotting at all, not to mention for rate of height change.

The AFCC, as expected has all the corrections we can think of.

OTOH, for train, FKC output TOTAL HA TRAINING CORRECTION , which will go though AFCC, which should make wind correction for train, than produce Gun training straight to the guns.

I am not sure about HACS, but for FKC the only way to understand this is that all spotting corrections are done by manipulating speed and angle of presentation.

[wmh829386]

The RN called it 'innocuous' shell for a reason. It was designed to minimize kill potential and maximize visibility and the charge was only large enough for that purpose.

Drones were not coming back riddled and the 5% figure included drones where the potential pilot was judged to have been incapacitated.

Might be a miscommunication there, I am referring to this.

The rub was that individual shells were not lethal enough. Again and again, drones came back to
base with numerous holes in them. That should not have been too surprising. Tests of 5in shell
fragmentation against an obsolete aircraft (an F7B) showed that the fragments were generally about
the size of a 0.50-calibre bullet. Earlier analysis of the 0.50 vs the 1.1in gun (see above) showed that
a 0.50 would be lethal only if it hit a vital spot. The larger impact-fused shell of the 1.1in was
considerably more lethal. The fleet was unhappy; it wanted larger fragments. BuOrd replied that the
larger the fragments, the smaller the volume they would cover, because there would be fewer of them,
and also because they would be given lower velocities...

It is quite possible that some WW2 shells have too much burster in it for splashing modern aircraft. Well, just speculation, and with VT fuze 5" seems to do fine anyway.

[Steve Crandell]

I'm somewhat confused. You said "PoW did quite well against level bombers at ~9000ft (IIRC) using radar, even with a substantial list and half her 5.25in armament OOCS". I'm not sure you addressed my question, which was whether a US ship could do as well PoW could do. If not, why not? You did say PoW was getting radar ranges, which was something US ships didn't have for quite some time. Of course even with radar ranges you can only fire accurately against level bombers, so maybe not worth it generally speaking. Against late war Kamikazes Mark 51 didn't use radar.

I believe I've read that most of the IJN aircraft shot down in the Pearl Harbor attack were victims of .50 MGs. Not too surprising since the FC organization of a lot of the ships wasn't functioning. What is surprising is how many were shot down, actually.

PoW's HAA stands out. It was accurate according to the IJN, and effective. Part of the reason is that the 5.25in gun had excellent ballistics and fired a very heavy shell, but her AA FC had to be good as well, and she repeated the performance in two separate formation attacks. The HADT4GB would be able to provide some measure of close range accuracy when using VT ammo via GRU/GRUB, however even using an eyeshooting sight as the HADT GO's sight or the slew sight on Mk37 should give reasonable kill probabilities when using VT ammo against directly approaching close range targets. Late war KGV was able to accurately engage low level IJN TE bombers, according to her gunnery report, using MT ammo and type 285P radar due to advances in HACS low angle FC.

Mk51 and 5in/38 could only engage close range targets and then only when using VT ammo, as it had no provision for controlling MT fuze setting. The Mk52 and Mk57 (IIRC) directors were similar but added radar ranging.

The USN actually expended about 10 thousand rounds of 3in and 5in ammo at Pearl Harbour but also ~14 thousand of rounds of 1.1in, ~300k rounds of .5in and 47K round of .3in, according the BuOrd's AA Summary.

I don't know if you realize this or if it's conscious effort, but you come across as believing that absolutely everything British is better than anything that was built in the USA and put on their ships. Even when British used American equipment, it was only because they couldn't produce their own superior equipment fast enough. Is this true? Over time, it sure seems like it. Americans are bumbling idiots and the only reason we did well in the Pacific or anywhere else was we built lots of stuff.

[dunmunro]

I'm somewhat confused. You said "PoW did quite well against level bombers at ~9000ft (IIRC) using radar, even with a substantial list and half her 5.25in armament OOCS". I'm not sure you addressed my question, which was whether a US ship could do as well PoW could do. If not, why not? You did say PoW was getting radar ranges, which was something US ships didn't have for quite some time. Of course even with radar ranges you can only fire accurately against level bombers, so maybe not worth it generally speaking. Against late war Kamikazes Mark 51 didn't use radar.

I believe I've read that most of the IJN aircraft shot down in the Pearl Harbor attack were victims of .50 MGs. Not too surprising since the FC organization of a lot of the ships wasn't functioning. What is surprising is how many were shot down, actually.

PoW's HAA stands out. It was accurate according to the IJN, and effective. Part of the reason is that the 5.25in gun had excellent ballistics and fired a very heavy shell, but her AA FC had to be good as well, and she repeated the performance in two separate formation attacks.

The HADT4GB would be able to provide some measure of close range accuracy when using VT ammo via GRU/GRUB, however even using an eyeshooting sight as the HADT GO's sight or the slew sight on Mk37 should give reasonable kill probabilities when using VT ammo against directly approaching close range targets. Late war KGV was able to accurately engage low level IJN TE bombers, according to her gunnery report, using MT ammo and type 285P radar due to advances in HACS low angle FC.

Mk51 and 5in/38 could only engage close range targets and then only when using VT ammo, as it had no provision for controlling MT fuze setting. The Mk52 and Mk57 (IIRC) directors were similar but added radar ranging.

The USN actually expended about 10 thousand rounds of 3in and 5in ammo at Pearl Harbour but also ~14 thousand of rounds of 1.1in, ~300k rounds of .5in and 47K round of .3in, according the BuOrd's AA Summary.

I don't know if you realize this or if it's conscious effort, but you come across as believing that absolutely everything British is better than anything that was built in the USA and put on their ships. Even when British used American equipment, it was only because they couldn't produce their own superior equipment fast enough. Is this true? Over time, it sure seems like it. Americans are bumbling idiots and the only reason we did well in the Pacific or anywhere else was we built lots of stuff.

I was responding to a number of different topics.

Four IJN level bomber attacks in 1941/42. PoW's fire does seem to have been more accurate than the 3 other level bomber attack examples in 1942.

Then late war FC using VT ammo which, of course, has relevance to how RN FC would fair against TD2C target drones. I am not sure how the late war FC examples are anything but neutral in tone.

I don't follow your last couple of sentences.

[wmh829386]

I'm somewhat confused. You said "PoW did quite well against level bombers at ~9000ft (IIRC) using radar, even with a substantial list and half her 5.25in armament OOCS". I'm not sure you addressed my question, which was whether a US ship could do as well PoW could do. If not, why not? You did say PoW was getting radar ranges, which was something US ships didn't have for quite some time. Of course even with radar ranges you can only fire accurately against level bombers, so maybe not worth it generally speaking.

Radar ranging is absolutely essential for any work besides close range, directly approaching targets. As the post war trial shows, Mk51 using fixed range setting of 2000 yards lost half its effectiveness. That is beside the issue that the Mk51 operator definitely learn the average range rate over the test, and perform even better than radar equipped systems.

A US ship with Mk37 and radar ranging should do better with one caveat: the gun crews must be well drilled to load with correct dead time. More importantly a Mk37 system could perform better against the TB attack, against which the PoW didn't do well at all with full battery and fighting trim.

[Steve Crandell]

I'm pretty sure Mark 37 dead time was set by the director. It was then up to the shell men to be consistent in how long it took them to remove the shell from the hoist fuse setter and place it in the loading tray. Most ships with 5"/38s had a loading trainer, so it's just a matter of training with that a lot so everyone is on the same page. I suspect that if you just load as fast as you can and you have lots of practice, the interval is going to be very consistent over a series of loads. I haven't seen loading trainers on British ships and I don't know if they even had them.

My understanding of what the British did was they simply set the delay for the anticipated range with zero dead time, loaded all the guns, and waited for the target to arrive at the correct range. That would be pretty precise, but result in an extremely low rate of fire. It would also save on ammo, which they seem to have been conscious of needing to do. And they would have relatively low RPK numbers for those aircraft they actually shot down.