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fire control - beginner's questions

 
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Bart150



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PostPosted: Fri Apr 18, 2008 8:36 am    Post subject: fire control - beginner's questions Reply with quote

I've been reading up on fire control at the time of Jutland, and I have a couple of beginner's questions about things I haven't seen covered explicitly - perhaps because other people think they too obvious to be mentioned:

Am I correct in assuming that normally both guns in a turret would use exactly the same firing solution?

Am I correct in assuming that normally each turrets would use a slightly different firing solution, and thus that the physical location of the turret on the ship was one more piece of data used in the calculation done by the Dreyer table in the TS?

If yes, would the TS have a separate Dreyer table for each turret - or would there be just one Dreyer table that was used once for each turret in turn?
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Euphraneous



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PostPosted: Fri Apr 18, 2008 11:12 am    Post subject: Reply with quote

You are correct in assuming that each turret would be positioned slightly differently in order for their gunfire to converge on one spot. Tony Lovell's excellent videos describe an offset to the firing solution that would be different for each turret, and that would vary depending on the range to the target. So the results from the one Dreyer table would be modified slightly for each turret. At least that's the way I remember the British system from the videos.

The Germans must have had some similar system, but I have yet to see any kind of detail on how their fire control worked.

The guns within one turret must have have been using the same firing solution. You wouldn't be able to direct the guns separately except for elevation, and that would only be useful for shooting at two targets that were in a direct line, but the nearer target would probably be obscuring the farther target, and it would be easier just to get another ship to shoot at one of the targets, or lacking another ship perhaps another turret acting independently, or if all your other turrets were out of action you still would be better off just aiming both guns at the nearer target.
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tone
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PostPosted: Fri Apr 18, 2008 3:53 pm    Post subject: Reply with quote

Eupraneous has it pretty right, and he impresses me with his comprehension of the tidal wave of information in those videos. I'm relieved that they come through in a sensible way.

The different turrets would converge in bearing on a target (up to a maximum angle of adjustment of 1.5 degrees, if I recall correctly). This made the most difference in broadside fire. This was needed in director fire, and was accomplished through a clever design of the training receivers in the turrets. In local firing, the separate trainer's own action in each turret of placing his scope on the target accomplished the same convergence more naturally and without a maximum angle, of course.

There was NOT a general means of converging in range (as might matter when firing well ahead of astern) in either mode of fire, but the tilt correction devices in each gun's elevation receiver could achieve some degree of this quite naturally through a brilliant (I was agog to look at it) tweaking. The approximation used was to select a "harmonizing range" (my term) at which range convergence would be completely and perfectly achieved. They'd select a range they expected to fight at (perhaps 12000 yards?). As the elevation of the guns wandered from that which would send the shells to this range, the convergence became diffuse. I think, however, that at no range was the pattern made less focused than it would have been with no such adjustments made at all.

There was no natural mechanism employed for range convergence in local mode that I know of, but it COULD be effected in the transmitting station, where the range master transmitter multiplexed out to the separate slave transmitters to relay its single figure to each turret and director. Each of the slave transmitters had a small range biasing knob with a differential that permitted the given slave transmitter to have a delta applied. A clever TS crew who wanted to achieve range convergence could paste a chart on the wall for which offsets in range were ideal for given relative firing bearings. I am not sure, however, that they ever did this. Indeed, I am not sure I know what these biasing knobs were intended to do.

A TS would have a single Dreyer table. If you look at the TS as a black box and leave out voicepipes and extraneous indicators having ancillary or control roles, its primary inputs are

1. speed of own ship (by a Forbes Log)
2. heading of own ship (by gyrocompass repeater)
3. wind direction and speed (probably by voice pipe, but perhaps by remote indicator from vane and anemometer)
4. target bearing (in an appalling 1/4 degree quantization) via electrical indication from a dumaresq aloft, often in the armored gunnery control tower
5. ranges in 25 yard quanta from each of the several rangefinders aloft, along with trigger wires indicating when each indication is deemed correct.
6. gun ready indicators for each main battery gun
7. trigger down indicator from the director
8. director training angle (decomposed as two step-by-step increments, "slewing and training")
9. director elevation angle (as step-by-step increments)

Within the TS, the Dreyer table generates a single continuous range and deflection to be broadcast to director and turrets/guns

The TS's outputs were simple, but where exactly they were sent was governed by large rotary change-over switches so that (for instance), it might be used to control just half the guns on the ship while other means (such as the second TS some ships carried) were used to direct the others against a separate target.

1. Range (in 25 yard quanta) to the director(s) and turrets indicated by the changeover switch -- as I indicated, each recipient could receive a manually tuned value, but I do not know that they ever received but the same range
2. Deflection or lateral aim-off angle (in "knots", or pips left or right from the line of sight to the target)
3. Firing signal (in director fire, this is simply being multiplexed out to the turrets from the arriving trigger down signal from the director. By sending it through the TS they obtained the advantage of flexible assignments of directors to turret groups and could also wire up a firing buzzer so they'd know when the guns went off and possibly also they had a break switch so they could enforce a gun safety when they wanted this. The last is my own inference... they may have judged having such switches as introducing excessive points of failure that could undermine the value of the entire scheme!
4. Director training angle (received actually as two incremental values), quantized to ... I forget. 4 arc minutes --- relayed as #3 to the selected turrets and also back to the director as a repeat indication
5. Director elevation angle -- an increment quantized to 1.5 arc minutes, if I recall correctly --- relayed as #3 to the selected turrets and also back to the director as a repeat indication

That's more detail than most want, and it has been awhile since I was knee-deep in this, but I think the above is right.

tone
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Euphraneous



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PostPosted: Sun Apr 20, 2008 2:33 pm    Post subject: Reply with quote

That's a lot of detail! Same with the videos. But I like detail. I would love to see a corresponding analysis of the German fire control system.
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PostPosted: Sun Apr 20, 2008 3:43 pm    Post subject: Reply with quote

I wish I knew enough to provide such.

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Bart150



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PostPosted: Mon Apr 21, 2008 9:17 am    Post subject: Reply with quote

Thanks, very much Tone. I don't want to seem liking I'm brushing aside all that interesting detail, but I'm still unclear about this basic question:

Did the TS send the same firing solution to all turrets (that were engaging the same target) or a different firing solution to each turret?

Then I have this other point. Is the following true or false?
The crew of the TS received data, followed predefined procedures that used a Dreyer table, produced an answer, and sent it out. They were not supposed to apply any judgement themselves. They would not, for example, say: 'That speed data we received sounds a bit high to us. We'll make it 2 knots less and feed that speed into the Dreyer table.'
Thus they functioned just like a modern computer program in the sense of garbage-in, garbage-out.
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PostPosted: Mon Apr 21, 2008 10:38 am    Post subject: Reply with quote

Bart150 wrote:
Thanks, very much Tone. I don't want to seem liking I'm brushing aside all that interesting detail, but I'm still unclear about this basic question:

Did the TS send the same firing solution to all turrets (that were engaging the same target) or a different firing solution to each turret?


Basically, yes.

In director fire, the DIRECTOR used data from the TS for deflection and range, and as it kept its scopes on the target, it then sent each turret all the same angle of training and each then corrected this a bit to converge on a point of ocean that was at the current gun range from the director. It also sent each turret a single gun elevation angle for an idealized gun, and each GUN's (not turret) elevation receiver then corrected this angle to account for a variety of factors (its degree of barrel wear, its difference in height from the director, the imperfect tilting of its turret from the pure vertical deck plane, etc)

In non-director fire, the TRANSMITTING STATION sent each turret a range and deflection. When the sightsetters in the turret adjusted their sights and the trainers and gun layers put their crosshairs on the target, the turrets would all converge in training but not in range -- their shells should all fall at the current gun range from each gun, plus or minus errors due to imperfect aim (by trainers or layers), quantization of range and deflection as sent from the TS, vagaries of the weapon itself, etc)

Quote:

Then I have this other point. Is the following true or false?
The crew of the TS received data, followed predefined procedures that used a Dreyer table, produced an answer, and sent it out. They were not supposed to apply any judgement themselves. They would not, for example, say: 'That speed data we received sounds a bit high to us. We'll make it 2 knots less and feed that speed into the Dreyer table.'
Thus they functioned just like a modern computer program in the sense of garbage-in, garbage-out.


I had said this is true, but at best it is partly true in that a Dreyer with bad data is simply going to be the scene of confused shrugging. But the function of a Dreyer-equipped TS is to use the Dreyer to make choices to minimize disagreement with the observations taken with the current state of the fire control solution as presently configured.

One great strength of the Dreyer table is that it allowed noisy (and sometimes quite garbage-like) data to be plotted and reviewed, and a human eye would be used to discern trends they felt the ranges and other data suggested. Humans are fairly good at seeing outlier samples in a data set and making a determination that that particular rangefinder might perhaps have seen things a little fuzzy or his instrument might be falling out of calibration somehow. Without putting these data into graphical form in a regular fashion, these discoveries and insights are very difficult to discern.

It is best to think of a Dreyer not as a computer, but as a fire control workbench. Imperfect observations of range and bearing are graphically analysed and used to select a speed and heading of the enemy ship that might plausibly account for the data being seen. At any given moment, the data might appear to disagree with this solution, and whether or not this disagreement is attributable to an imperfect guess at enemy range, speed and heading or simply to errors in the observations themselves. Thus, the Dreyer is a tool for comparing observations to the current indications of a firing control solution, and it helpfully simulates that solution over time ("integration" this is often called). But it does not crunch inputs and simply hand you an answer like a thermometer, and I think that is a key strength.

A TS team might notice and offer suggestions if they saw discrepancies between the range, range rate, bearing rate and such being used and the range and bearing reports they were plotting, but the decision as to whether to alter the enemy's speed or heading to rectify this discrepancy was reserved to the range officer who was aloft and unable to see the plot.

For instance, if the Dreyer table had a range rate on it of "closing 400", and the table officer in the TS saw a weak correlation of recently plotted ranges that suggested that the range was actually opening at 200 yards per minute, he might speak through a voice tube or phone to the range officer and say, "A fair rate is 200 opening", to which the range officer might examine his little dumaresq to see what speed and inclination (heading, basically) of the enemy this would imply and compare it to what his eyes told him and how much he trusted his own perception. He might then choose to accept the suggestion or ignore it or command another value in compromise.

In this way, the data plots maintained below and the relationship between firing and target ship visible from aloft would be part of a scientific debate of what was actually happening. Dumaresqs were valuable tools in helping people relate these two dissimilar descriptions of the solution (e.g., describing enemy motion in terms of range rate and bearing rate versus describing his motion in terms of speed and inclination).

I hope that's not too confusing.

Your answer is best described as "true" in terms of the fact that garbage-in means garbage-out, and this is why I am fully satisfied that the Dreyer tables did not themselves account for poor RN gunnery at Jutland or elsewhere. The poorest shooters at Jutland had little data for ranges and it was poor indeed. The least correct observations were long held as the ones to shoot with, and misses resulted.

Alternative computing machinery would not have improved their shooting, and indeed, a completely Pollenesque TS (all Argo gear) would likely have done worse owing to its lack of support for fielding and choosing between the most precious data available to the team: range cuts from a plurality of rangefinders.

You will find many people who disagree with this, but I feel that rational review of their claims show they dwell on inconsequential niceties the Royal Navy passed on when it did not adopt Argo fire control technology on a whole-hog basis and ignore the basic issues which actually caused the Royal Navy to disappoint the British people in their gunnery in a few short and crucial tests of history.

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Bart150



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PostPosted: Mon Apr 21, 2008 11:18 am    Post subject: Reply with quote

Wow, thanks a lot.
I'll have to think about it some more before I know whether it is confusing or not.

I do have another point, albeit somewhat off-topic.
I understand that the crew of the TS in a Dreadnought were normally a Royal Marine band (musician was their day job, so to speak).
I'm interested in the fate of HMS Monmouth, the non-Dreadnought armoured cruiser sunk at Coronel in 1914 (a relative of mine on board). The casualty list includes a Royal Marine band. D'you think they worked in a TS with a Dreyer table too?
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PostPosted: Mon Apr 21, 2008 1:07 pm    Post subject: Reply with quote

Likely, they'd have been in the TS, but they would not have had a Dreyer table in that ship at that date.

I can supply more info later

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Bart150



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PostPosted: Fri Sep 05, 2008 10:06 am    Post subject: Reply with quote

Tone,
I don't want to be pushy, just wondering if you had any more information on this
Bart
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PostPosted: Fri Sep 05, 2008 11:10 am    Post subject: Reply with quote

Hi, I haven't looked further into this, really. The Dreyer tables were still being deployed early in the war, with priority given to the dreadnoughts and battlecruisers. Indeed, neither the Invincible nor Inflexible seem likely to have had Dreyers fitted for the Falklands battle (a fact that doesn't keep this battle as being cited as an example of the tables' poor functioning!)

Moreover, the RN ACs at Coronel did not have directors. The decision to extend director provisioning to ACs was not made until November 1914, and the 8 ACs to be so equipped were likely newer ones destined to support the Grand Fleet. This order was lent greater specificity on Jan 2 1915, when it was decreed that Minotaur, Duke of Edinborough and Achilles classes of ACs were to receive directors, but no older ACs. (source for this paragraph is "Fire Control in HM Ships", 1919)

No matter what technologies were available at a given date, it was generally the case that the bigger ships had the more deluxe gear -- a trend that reflected the greater strength of these vessels as well as the greater space and displacement available for such power-multiplying equipment.

An armored cruiser would likely have had a TS with plotting equipment, even if little more than manual plotting boards. A Vicker's clockwork range-clock would have been used to try to manage a range with a linear range rate which would have been calculated from plotted data and/or a dumaresq set to observed/estimated enemy speed and inclination.

The people in the TS may have been bandsmen. That was common, but I'm not sure if it was universal.
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Bart150



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PostPosted: Fri Sep 05, 2008 11:30 am    Post subject: Reply with quote

Thanks, Tone.
Monmouth was a Devonport ship with a crew hastily assembled from men mainly of port division Devonport, who hardly knew each other when the ship sailed. But she had a Marine band whose men exceptionally were all from port division Portsmouth.
It looks as if the ship was short of TS personnel and these men were a complete team rushed over from Portsmouth. I suppose the less automated the control system, the more important practice and teamwork would be. I can't see why otherwise they'd have gone to that trouble to get a band on board.
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