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

Guns, torpedoes, mines, bombs, missiles, ammunition, fire control, radars, and electronic warfare.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

wmh829386 wrote: Sun Jan 16, 2022 11:49 pm
dunmunro wrote: Sun Jan 16, 2022 9:54 pm
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.
OK, I was referring to this summary:
A study of the results of antiaircraft firings by the ships of the Fleet,
from July 1, 1938 to June 30, 1940, gave little cause for cheer or hope for
solution in this area. This study showed that in 307 firing runs by 1.1",
3", and 5" antiaircraft guns against high-altitude, horizontal-bombing
drone aircraft, dive-bombing drone aircraft, and low-altitude, horizontal-
bombing drone aircraft, only 5% of the drone target aircraft had been
hit seriously enough to stop the bombing attack and only 17% hit at all.""
Regarding fragment size: The Deadly Fuze has data on that and larger bursters increased lethality even with smaller but more numerous fragments. (these were using mockup IJNAF 'Kate' targets) The large VT fuze also reduced the efficacy of RN 4.5in and 5.25in ammo due to a reduction in burster size. In a separate book, it was stated that the reduction in efficacy was smaller than feared because the resulting fragments were larger and more lethal per fragment.

The Deadly Fuze also discusses the use of small black powder charges in VT ammo by the US Army, who were anxious to preserve target drones, after they witnessed the USN destroying a number of drones in the initial ship 5in VT vs drone trials. On the first trial a small Army drone was destroyed at 10k yds! Fortunately this was not repeated against additional drones, even though TTBs were generated and the initial drone hit was described as a fluke direct hit!
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

wmh829386 wrote: Mon Jan 17, 2022 2:08 am
Steve Crandell wrote: Sun Jan 16, 2022 8:28 pm 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.
In the wartime anti-suicide attack summaries the USN stated that Mk51/5in VT was considerably more effective against actual kamikazes than Mk37/Mk1 computer using 5in VT:
Virtually all combatant vessels and many auxiliaries are equipped to control their heavy AA. guns from some form of a lead-computing director (Marks 51, 52, 57, and 63) either as primary control in the case of the lesser ships, or as auxiliary directors in large combatant ships, with cross-connection to an adjacent 40mm. director. This type of director provides marked improvement in speed and flexibility of control of the heavy AA. batteries and suffers much less from evasive tactics of a close-in target than do the slower primary director systems. The accuracy and effectiveness of their control depends on skill of the director pointers, the accuracy of the range setting and the ballistics of the director.

The diagrams at the end of this chapter indicate errors to be expected as a result of improper ballistics and indicate range values within which the fire is effective for the 40mm. using 5-inch ballistics. The errors for the reverse process are almost identical, with the exception that the 5-inch fire then leads the target - a not undesirable situation. Analysis of previous experience with 40mm. mounts and the Mark 51 director, with estimated range setting, indicates errors on the order of 15-20 mils at ranges between 1,000 - 4,000 yards. With VT fuzes and such control the probability that a suicide plane brought under fire inside of 4,000 yards will survive is considerably less than one-third its survival probability if the primary director control system is used. http://www.ibiblio.org/hyperwar/USN/rep ... ary-4.html
I suspect that the low speed of the TD2C drone gave Mk37/Mk1 an unfair advantage in the postwar drone trials
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

Steve Crandell wrote: Mon Jan 17, 2022 3:02 am 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.
The RN set DT at the HACT/FKC and then ensured that each salvo had identical fuze timing via a fuze and load lamp system (controlled automatically in the HACT/FKC) at the fuze setter and gun mount. A lamp told the fuze setter when to set the fuze and another lamp told the loader when to place the shell in the loading tray or breech. MK37 also set DT at the Mk1 computer, based upon the average gun crew loading cycle, but had no control of the loading cycle after the gun was fired.

The RN ABU used zero deadtime via preloaded fuzed shells, and the ABU used radar ranging to fire the guns at the correct moment so that the ToF to the target matched the fuze time. ABU was most useful for, typically, 6in guns that didn't have HACS/FKC FC control.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

dunmunro wrote: Mon Jan 17, 2022 5:05 am

In the wartime anti-suicide attack summaries the USN stated that Mk51/5in VT was considerably more effective against actual kamikazes than Mk37/Mk1 computer using 5in VT:

That is in very good agreement with the test. Mk51 performs even better than Mk57 and Mk63 in some particular ranges. There 2 reasons for that.

1. Range /range rate estimate in actual operation is readily available from Air warning sets / operator experience.

2. The lighter mount without radar antenna is more handy for manuvering targets.

3. The wrong ballistic of the 40 mm that overlead the target is actually more conducive to TTB than the "correct lead"
(E.g. The performance of Mk51 HMG at 4000 yards)
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

Steve Crandell wrote: Mon Jan 17, 2022 3:02 am 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.
The main difference is that when using MT fuse, HACS always fire in salvo. So loading cycle is strictly controlled. For Mk37, it's always continuous aim and it is up to the gun crews to keep the dead time
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

wmh829386 wrote: Fri Jan 14, 2022 3:56 pm
The amount of lag in a contemporary 4.5" FC, (GRU + HACSIV) is excessive to put it mildly.

Firstly, rates are produced by GRU, which the GRUB operator matches with speed and inclination. (height and range are supplied).
Secondly, the deflection screen operator produce deflection with information from GRUB.
Thirdly, FTP by 4.5" gunners. While all the limitations and assumptions of HACS still applies.

GRUDOU eliminated much of the lag and throw out the constant height assumption, hence the improvement in performance. Keep in mind the performance of Mk37 is comparable to other relative rate systems from 2000 yards to 4000 yards, i just don't see how HACS would keep up using GRUB and HACT.
The idea that GRU/GRUB provides "short range" accuracy is ludicrous. Yes, GRU is only considered accurate enough below 4000 yards. However the system it paired with is the antithesis of a good short range system.

1. Data goes through 3 followers in succession, lag is a big issue.
2. Constant height assumption that is not valid except for level bombing
3. Salvo firing is needed, so rate of fire suffers.

Hence for attack types other than level bombing, GRU/GRUB only have a very small window of effective range before fire is switched to barrage. Even with VT fuse removing the third factor, radical manuvers will prompt the GO to start eyeshooting immediately.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

wmh829386 wrote: Sun Jan 16, 2022 11:18 pm
dunmunro wrote: Sun Jan 16, 2022 9:58 pm
wmh829386 wrote: Sun Jan 16, 2022 9:00 pm

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.

These are all the FKC operator inputs from an incomplete manual:

Mk2* FKC

Fuze Prediction section

Target travel correction handwheel

Ballistic Height Correction handwheel

Range Tuning handwheel

Rate Spotting handwheel

Target Speed handwheel

Target travel correction handwheel

Deflection Calculation Section

Log APV Handwheel
Last edited by dunmunro on Mon Jan 17, 2022 7:34 pm, edited 1 time in total.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

wmh829386 wrote: Mon Jan 17, 2022 6:21 pm
wmh829386 wrote: Fri Jan 14, 2022 3:56 pm
The amount of lag in a contemporary 4.5" FC, (GRU + HACSIV) is excessive to put it mildly.

Firstly, rates are produced by GRU, which the GRUB operator matches with speed and inclination. (height and range are supplied).
Secondly, the deflection screen operator produce deflection with information from GRUB.
Thirdly, FTP by 4.5" gunners. While all the limitations and assumptions of HACS still applies.

GRUDOU eliminated much of the lag and throw out the constant height assumption, hence the improvement in performance. Keep in mind the performance of Mk37 is comparable to other relative rate systems from 2000 yards to 4000 yards, i just don't see how HACS would keep up using GRUB and HACT.
The idea that GRU/GRUB provides "short range" accuracy is ludicrous. Yes, GRU is only considered accurate enough below 4000 yards. However the system it paired with is the antithesis of a good short range system.

1. Data goes through 3 followers in succession, lag is a big issue.
2. Constant height assumption that is not valid except for level bombing
3. Salvo firing is needed, so rate of fire suffers.

Hence for attack types other than level bombing, GRU/GRUB only have a very small window of effective range before fire is switched to barrage. Even with VT fuse removing the third factor, radical manuvers will prompt the GO to start eyeshooting immediately.


This is from The Deadly Fuze:
The navy's Mark 37 gun director was a heavy unit,
designed to control a bank of guns for surface and long
range firing. It was slow to reach a solution and used long
smoothing times, not adaptable to modern antiaircraft work
where targets were close in and maneuvering rapidly from
several different directions at once. Since there was only
one such director per ship normally, only one target could
be engaged at a time. With time fuzes, one director had to -
control all available guns, but with VT fuzes each gun or
twin mount needed its own director. Efforts on fire control
were initiated after a forceful report by Dennison,
Tuve realized that the creation of a new fire control
system was a logical outgrowth of the development of the
Proximity Fuze...
It's my understanding that Mk51 sent data to 5in gun mounts via the FtP indicators.

1) So Mk37/Mk1 had lag issues too, and as I've stated, IMHO, the slow speed of the TD2C helped mask these issues.
2) The GO can compensate for altitude change and FC team also. With Mk37 it is suggested to enter a false speed and rate control downward, similarly there's no way that Mk37 could receive accurate altitude change rate data, especially with a diving and accelerating target.
3) Barrage fire (via eyeshooting) is used when target range is likely to fall below the minimum range/engagement envelope for accurate fuze setting (ditto for Mk37 who also used it with MT fuzes) but this is not applicable to VT fuzed ammo using GRUB. The loaders can ignore the load lamp and load as fast as possible since the FKC/HACS/GRUB will continue to generate a FC solution.

This is from Pout (who worked as a FC scientist during WW2):
Rf/Rp/ToF/no GRU Kp/GRU Kp
6/ 7.6/ 10/ 1 in 250 shots / 1 in 185 shots
4/5.2/ 6/ 1 in 70 shots / 1 in 50 shots
3/ 4.0/ 4/ 1 in 40 shots / 1 in 30 shots

Pout states that in practise GO's reported little to no improvement with GRU/GRUB but it's unlikely that a single ship or HADT GO would have fired enough VT to come to an accurate conclusion.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

dunmunro wrote: Mon Jan 17, 2022 6:25 pm
wmh829386 wrote: Sun Jan 16, 2022 11:18 pm

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.

These are all the FKC operator inputs from an incomplete manual:

Mk2* FKC

Fuze Prediction section

Target travel correction handwheel

Ballistic Height Correction handwheel

Range Tuning handwheel

Rate Spotting handwheel

Target Speed handwheel

Target travel correct handwheel

Deflection Caculation Section

Log APV Handwheel
Thanks, that probably take some digging. Good to know that at least there is a ballistic height correction, that's better than nothing. I doubt any GO enjoys guessing rate of height change and calculating the correction on the fly, which is changing as the ToF of shell changes, even in steady decent/glide.

However, there is no wind correction.
Range tunning -> match radar/RF range
Rate spotting -> match radar range rate (hence update speed)
Speed -> initial speed estimate from GO
Target travel correction -> update target heading after provided from angle of presentation
Log APV -> Function of height and plane range + gun wear.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

dunmunro wrote: Mon Jan 17, 2022 6:53 pm
It's my understanding that Mk51 sent data to 5in gun mounts via the FtP indicators.

1) So Mk37/Mk1 had lag issues too, and as I've stated, IMHO, the slow speed of the TD2C helped mask these issues.

2) The GO can compensate for altitude change and FC team also. With Mk37 it is suggested to enter a false speed and rate control downward, similarly there's no way that Mk37 could receive accurate altitude change rate data, especially with a diving and accelerating target.

3) Barrage fire (via eyeshooting) is used when target range is likely to fall below the minimum range/engagement envelope for accurate fuze setting (ditto for Mk37 who also used it with MT fuzes) but this is not applicable to VT fuzed ammo using GRUB. The loaders can ignore the load lamp and load as fast as possible since the FKC/HACS/GRUB will continue to generate a FC solution.

This is from Pout (who worked as a FC scientist during WW2):
Rf/Rp/ToF/no GRU Kp/GRU Kp
6/ 7.6/ 10/ 1 in 250 shots / 1 in 185 shots
4/5.2/ 6/ 1 in 70 shots / 1 in 50 shots
3/ 4.0/ 4/ 1 in 40 shots / 1 in 30 shots

Pout states that in practise GO's reported little to no improvement with GRU/GRUB but it's unlikely that a single ship or HADT GO would have fired enough VT to come to an accurate conclusion.
1) The report matches war experience well. Strange to think the test masked the issue of Mk37.
2) No false input is used for Mk37 for change in height. There's nothing false in adding negative vertical rates for diving target. Furthermore if the director is tracking for some time, the Mk1 should be in Automatic where operator just keep the director on target. And if target stays in a constant rate dive long enough (~order of 10s) the FC solution will converge with the correct rates.
The point is, even at longer ranges (~4000 yards), the lag due to human follow-up makes the GRU+GRUB pointless because the GRUB operator cannot follow the output of GRU fast enough AND height change will cause further confusion in "GRU speed" and heading because of its assumption.
3) Does Pout's calculation distinguished GRUB with GRUDOU?
A scientist will immediately dig into the issue of calculation doesn't match empirical data.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

wmh829386 wrote: Mon Jan 17, 2022 8:47 pm
2) No false input is used for Mk37 for change in height. There's nothing false in adding negative vertical rates for diving target. Furthermore if the director is tracking for some time, the Mk1 should be in Automatic where operator just keep the director on target. And if target stays in a constant rate dive long enough (~order of 10s) the FC solution will converge with the correct rates.
The point is, even at longer ranges (~4000 yards), the lag due to human follow-up makes the GRU+GRUB pointless because the GRUB operator cannot follow the output of GRU fast enough AND height change will cause further confusion in "GRU speed" and heading because of its assumption.
3) Does Pout's calculation distinguished GRUB with GRUDOU?
A scientist will immediately dig into the issue of calculation doesn't match empirical data.
2) Rate of altitude change is dependent on target speed and angle of climb and if target speed is wrong then so is rate of altitude change and the whole setup becomes 'false' but what matters is not a 'false' setup but the resulting FC solution and whether it increases the accuracy of fire. 10 secs seems like a 'lag' to me. We don't know anything about the inherent lags in GRU/GRUB or HACS/FKC but I suspect they were less than the inherent time to solution in a mechanical linear rate tachymetric computer.

3) Yes, Pout describes the various errors that resulted in HACS kill probabilities for each example case. Hence the small change when GRUB was added using MT fuzes. He states that the increase in kill probability with VT was entirely due to the elimination of dead time and of fuze timing errors whilst using the other parameters of HACS+RADAR / HACS+RADAR+GRU. Pout states that the HACS teams were already successfully overcoming HACS limitations via 'work arounds' and these negated the advantages of the GRU.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

dunmunro wrote: Tue Jan 18, 2022 1:42 am
wmh829386 wrote: Mon Jan 17, 2022 8:47 pm
2) No false input is used for Mk37 for change in height. There's nothing false in adding negative vertical rates for diving target. Furthermore if the director is tracking for some time, the Mk1 should be in Automatic where operator just keep the director on target. And if target stays in a constant rate dive long enough (~order of 10s) the FC solution will converge with the correct rates.
The point is, even at longer ranges (~4000 yards), the lag due to human follow-up makes the GRU+GRUB pointless because the GRUB operator cannot follow the output of GRU fast enough AND height change will cause further confusion in "GRU speed" and heading because of its assumption.
3) Does Pout's calculation distinguished GRUB with GRUDOU?
A scientist will immediately dig into the issue of calculation doesn't match empirical data.
2) Rate of altitude change is dependent on target speed and angle of climb and if target speed is wrong then so is rate of altitude change and the whole setup becomes 'false' but what matters is not a 'false' setup but the resulting FC solution and whether it increases the accuracy of fire. 10 secs seems like a 'lag' to me. We don't know anything about the inherent lags in GRU/GRUB or HACS/FKC but I suspect they were less than the inherent time to solution in a mechanical linear rate tachymetric computer.

3) Yes, Pout describes the various errors that resulted in HACS kill probabilities for each example case. Hence the small change when GRUB was added using MT fuzes. He states that the increase in kill probability with VT was entirely due to the elimination of dead time and of fuze timing errors whilst using the other parameters of HACS+RADAR / HACS+RADAR+GRU. Pout states that the HACS teams were already successfully overcoming HACS limitations via 'work arounds' and these negated the advantages of the GRU.
2) Apparently you can just ignore the lag due to 3 operators in flow of data. Worse still, the GRUB operator has the unenviable job of matching speed and inclination to elevation rate and train rate. It is not a simple FtP nor aligning pair of cross-wires. Worse still, if the target is changing height, matching the GRU rates will produce the wrong speed and inclination . Meaning the FC solution cannot be reached. And the GO have to intervene with spotting corrections. All of that takes time.
Rate estimates input to Mk37 will be tune either manually or automatically, converging to the correct setup. Even with in maual rate control, the operator is visually looking at the target rather than below deck try to match rates that perhaps should not be matched at all :stubborn: .

3)My question is whether GRUDOU is included in the analysis. We all know it and the GRU ends up becoming the literal work around the HACT, rather then this bizarre claim of HACS working around the GRU.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

dunmunro wrote: Sun Jan 16, 2022 10:04 am
wmh829386 wrote: Sun Jan 16, 2022 3:05 am

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.
From the FKC Handbook:
In ships carrying the A.F.C.C. Mark 1 the total elevation correction found by the fuze
keeping clock is added to director elevation in the fuze keeping clock and then transmitted
through the gun elevation synchronous unit direct to the guns. In later ships carrying the
A.F.C.C. Mark 1** the total deviation correction is added by follow-through magslip to director
elevation in the gun elevation synchronous unit.
In ships carrying the transit the total elevation correction found by the fuze keeping clock
is transmitted electrically to the transit which produces gun elevation and transmits it to the guns.
In ships carrying the fire control box the total elevation correction found by the fuze
keeping clock is transmitted mechanically to the fire control box where it is added to director
elevation and transmitted as gun elevation to the guns.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

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

Post by dunmunro »

wmh829386 wrote: Tue Jan 18, 2022 6:43 am
dunmunro wrote: Tue Jan 18, 2022 1:42 am
wmh829386 wrote: Mon Jan 17, 2022 8:47 pm
2) No false input is used for Mk37 for change in height. There's nothing false in adding negative vertical rates for diving target. Furthermore if the director is tracking for some time, the Mk1 should be in Automatic where operator just keep the director on target. And if target stays in a constant rate dive long enough (~order of 10s) the FC solution will converge with the correct rates.
The point is, even at longer ranges (~4000 yards), the lag due to human follow-up makes the GRU+GRUB pointless because the GRUB operator cannot follow the output of GRU fast enough AND height change will cause further confusion in "GRU speed" and heading because of its assumption.
3) Does Pout's calculation distinguished GRUB with GRUDOU?
A scientist will immediately dig into the issue of calculation doesn't match empirical data.
2) Rate of altitude change is dependent on target speed and angle of climb and if target speed is wrong then so is rate of altitude change and the whole setup becomes 'false' but what matters is not a 'false' setup but the resulting FC solution and whether it increases the accuracy of fire. 10 secs seems like a 'lag' to me. We don't know anything about the inherent lags in GRU/GRUB or HACS/FKC but I suspect they were less than the inherent time to solution in a mechanical linear rate tachymetric computer.

3) Yes, Pout describes the various errors that resulted in HACS kill probabilities for each example case. Hence the small change when GRUB was added using MT fuzes. He states that the increase in kill probability with VT was entirely due to the elimination of dead time and of fuze timing errors whilst using the other parameters of HACS+RADAR / HACS+RADAR+GRU. Pout states that the HACS teams were already successfully overcoming HACS limitations via 'work arounds' and these negated the advantages of the GRU.
2) Apparently you can just ignore the lag due to 3 operators in flow of data. Worse still, the GRUB operator has the unenviable job of matching speed and inclination to elevation rate and train rate. It is not a simple FtP nor aligning pair of cross-wires. Worse still, if the target is changing height, matching the GRU rates will produce the wrong speed and inclination . Meaning the FC solution cannot be reached. And the GO have to intervene with spotting corrections. All of that takes time.
Rate estimates input to Mk37 will be tune either manually or automatically, converging to the correct setup. Even with in maual rate control, the operator is visually looking at the target rather than below deck try to match rates that perhaps should not be matched at all :stubborn: .


3)My question is whether GRUDOU is included in the analysis. We all know it and the GRU ends up becoming the literal work around the HACT, rather then this bizarre claim of HACS working around the GRU.
2) I'm not ignoring it, but I know from watching videos of pointer matching, that the lag in each case is on the order of a fraction of a second. The conversion of speed and inclination is done by the GRUB - that's what the GRUB is for! The GRUB also adds conversion factors that correct for inherent errors in the HACS:
When G.R.U.B. is fitted corrections are applied to angle of presentation and
target speed to suit the inherent errors of the H.A.C.S. (HACS III Manual)
Manual rate control on Mk37/Mk1 computer:
In Manual Control of rates, corrections to Target Speed and
Target Angle and Rate of Climb are estimated by the Computer
Crew with the aid of continuous Director observations of Tar-
get Position...

The Observed Changes of Target Position in relation to Own
Ship in Range, Elevation, and Bearing are continuously sent
from the Director to the Computer by synchro transmission.
Observed Changes of Target Position show up on the Com-
puter as rotation of three sets of dials: the outer Elevation
Dials, the outer Bearing Dials, and the inner Range Dials. These
are the Observed Dials...

Since Observed Elevation is continuously received in Manual
Rate Control, Manual Rate Control may also be used against
air targets. However, the short duration of air problems and
the complexities of target movement in three dimensions make
Manual Rate Control against air targets difficult. Manual Rate
Control against air targets may be regarded as an auxiliary type
of operation, while Manual Rate Control against surface tar-
gets is a normal type of operation.
3) GRUDOU is NOT included in the analysis:

Rf/Rp/ToF/no GRU Kp/GRU Kp
6/ 7.6/ 10/ 1 in 250 shots / 1 in 185 shots
4/5.2/ 6/ 1 in 70 shots / 1 in 50 shots
3/ 4.0/ 4/ 1 in 40 shots / 1 in 30 shots

The first column is for HACS+Radar. The 2nd is for HACS+RADAR+GRU/GRUB
Pout:
...Nevertheless this was a tachometric
system, and rate was determined directly by a method that avoided the
catastrophic results of differentiation of erratic sight-line motions already
discussed. A unit - the Gyro Rate-Unit Box (GRUB) - at the HAC
position, when fed with data from the Gyro-Rate Unit (GRU), could
convert these rates directly into inputs to the HAC Table for the usual
processes of conversion into gun orders, using radar range as described
in Case 2. Again there was the option for operators at the Table not to use
the GRU rates when the circumstances made them unreliable, since
director elevation and training data were also available at the Table for
present position, as before...
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

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

Post by wmh829386 »

2) According to Friedman, it's not a simple FtP. Rather a feedback process more similar to rate control with the unfortunate caveat that it is subjected to the limitations of HACS assumptions (and god help you if a fictitious input have been used for wind correction)
Ships completed in 1940 had a new Gyro Rate Unit (GRU) mounted on the director, to measure horizontal and vertical angular rates directly. Although this measurement might be described as tachymetric, it could not transform the HACS into something capable of dealing with climbing or diving targets. Nor did it solve the problem of measuring target inclination. That was still fed in by the control officer.
The Gyro Rate Unit Box (GRUB) in the calculating position below decks received the two rates and the angle of presentation from the GRU, ultimately to feed data into the HACT nearby. This was still a feedback process. The assumed target ground (plan) speed was set on the GRUB. Given an angle of presentation and a target height and range, this speed implied particular vertical and horizontal rates. It was adjusted until these rates matched the observed rates, the GRU acting in effect as a feedback mechanism.
Your quote of Mk37 manual just shows the time for FC solution to converge in Automatic mode for Mk37 is typically faster tham matching rates even when looking directly at the target.

3) This is hilarious. :lol:

The mode of operation without GRU:
HACS output director sight angles and (clock=radar) range to electric height finder. So the GO adjust the speed and angle of presentation until the electric height finder stays on target. In other words, rate control without provision of climb rate.

According to Mk37 manual, automatic mode is more suitable for manuvering targets anyway.

With that in mind, I doubt he is calculating for targets that violates assumptions of HACS, a case which is amost impossible to quantify.
Post Reply