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Old 07-14-2014, 02:08 PM   #21
Kromm
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

Quote:
Originally Posted by sir_pudding View Post

How did you handle the FDC?
It never came up, to be honest. For one PC peeking out and observing the fires of another PC's mortar, there was no need – there were two people involved (one with Forward Observer, one with Artillery) and they interacted directly. For PCs calling in off-map fires, it was irrelevant . . . the entire apparatus from "the other end of this radio call" to "shells falling over there" was a black box.
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Old 07-14-2014, 02:11 PM   #22
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

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Originally Posted by Kromm View Post
It never came up, to be honest. For one PC peeking out and observing the fires of another PC's mortar, there was no need – there were two people involved (one with Forward Observer, one with Artillery) and they interacted directly. For PCs calling in off-map fires, it was irrelevant . . . the entire apparatus from "the other end of this radio call" to "shells falling over there" was a black box.
Probably the one operating the gun was doing the math, there?
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Old 07-14-2014, 02:13 PM   #23
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

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Originally Posted by Kromm View Post
It never came up, to be honest. For one PC peeking out and observing the fires of another PC's mortar, there was no need – there were two people involved (one with Forward Observer, one with Artillery) and they interacted directly. For PCs calling in off-map fires, it was irrelevant . . . the entire apparatus from "the other end of this radio call" to "shells falling over there" was a black box.
How did the Mortar team adjust fire without fire direction? You can't just take "Left Five-Zero Up Two-Five" and translate that directly into Deflection, Charge and Elevation for the mortar sight. Remember that the FO is using a carestian system with himself at the origin and the gunline is a polar system with the adjusting gun as the origin. It isn't trivial to translate between the two systems.
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Old 07-14-2014, 02:25 PM   #24
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

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Originally Posted by sir_pudding View Post

How did the Mortar team adjust fire without fire direction? You can't just take "Left Five-Zero Up Two-Five" and translate that directly into Deflection, Charge and Elevation for the mortar sight. Remember that the FO is using a carestian system with himself at the origin and the gunline is a polar system with the adjusting gun as the origin. It isn't trivial to translate between the two systems.
I generally assume that if two PCs are working this way, they have some means of handling the situation. If that means unrealistically letting them "translate" in their heads, so it goes . . . the penalty for doing that is canceled by a bonus for advance prep. It doesn't bug me that much because at the TLs where this has come up, field glasses with computers built in, gunsights with computers built in, and networks that link the two are commonplace, and the PCs just about always have a surfeit of techies.
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Old 07-14-2014, 05:42 PM   #25
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

I found some years ago some WW II US military manuals on line which included some on artillery gunnery. I'm no expert but, IIRC, this is what I remember for mortars . . .

You have a marker, an "aiming stake," set up some distance from the mortar tube. This is a reference for azimuth change.

In c. 1941 the US Army had its sights measured in "infantry mils". One infantry mil is 1/6400 of a full circle; there are c. 17.8 such mils to a degree.

A displacement of one mil of azimuth will be about 1/1000th of the range. (Actually, for an infantry mil it's 1.01 thousandth -- but that error will be lost in the normal error of the shell's flight.)

So if you're firing at 800 yards, and you're dropping rounds at the right range and 50 yards left, you use the sight and come right about 50 yards divided by point-8 mils ({800 yards divided by 1000} mils, or c. 62.5 mils).

It's complex, and requires some mental gymnastics in combat, but long training usually produces adequate results.

For range, most mortarmen have a pretty good idea of how much a change in elevation of a few mils will alter the point of impact at what range. For more precise work, every set of mortar shells will have a range card, showing this information at various ranges & elevations. You have to correct, of course, for differences in elevation between yourself & the target, wind, humidity, and, if at enough range, the rotation of the earth.

Example -- the observer says "Left fifty yards, down sixty." Mr. Mortarman says to himself (in those days, always himself) "At eight hundred yards that's 62.5 mils. So he adjusts the dial sight on the mortar tube 62.5 mils to the right (which moves the barrel to the left). He then turns the traversing crank and re-aligns the sight on the aiming stake. Now he's fixed for azimuth.

"Range -- to drop about sixty yards with this weapon & this charge at this range I need to raise [for mortars, to shorten range you increase elevation] the tube about (figure out of my [deleted]) 75 mils." Add 75 mils to the bubble sight on the tube. Crank, crank on the elevating handle until the bubble comes level again. Then either tell the observer "Round on the way!" or simply drop-shoot the round and assume Joe Observer knows the sound of a round departing the tube.

I'd expect that a good mortarman would accomplish all this in a fraction of the time it takes me to tell it.

[If I'm in error I invite editorial correction.]

This is why for most of the last 150 odd years the artillery tries to get smart officers & NCOs to do all this under fire.
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Old 07-14-2014, 09:55 PM   #26
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

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Originally Posted by fredtheobviouspseudonym View Post
I found some years ago some WW II US military manuals on line which included some on artillery gunnery. I'm no expert but, IIRC, this is what I remember for mortars . . .
I can't answer to the Second World War directly, but I can tell you that the primary method I was trained to use, used equipment and techniques that were extremely low-tech and that were all introduced in their current form during the Vietnam war. I've seen the WWII era equipment in museums and they only differ in some details and materials of construction. The method you describe, for reasons of geometry can't have been used during WWII, however, as it simply can't have ever worked.
Quote:
You have a marker, an "aiming stake," set up some distance from the mortar tube. This is a reference for azimuth change.
This is essentially true, although you actually use three stakes (a direction stake and two aiming stakes (near and far)) this compensates for changes in the gun's lay as it is fired and some other error checking functions. You also have a "red" backstake that allows for missions "behind" the mortar position.

Quote:
In c. 1941 the US Army had its sights measured in "infantry mils". One infantry mil is 1/6400 of a full circle; there are c. 17.8 such mils to a degree.
This is correct.

Quote:
A displacement of one mil of azimuth will be about 1/1000th of the range. (Actually, for an infantry mil it's 1.01 thousandth -- but that error will be lost in the normal error of the shell's flight.)
This is also correct.

Quote:
So if you're firing at 800 yards, and you're dropping rounds at the right range and 50 yards left, you use the sight and come right about 50 yards divided by point-8 mils ({800 yards divided by 1000} mils, or c. 62.5 mils).
No. This would only work if the FO was located exactly on the adjusting gun, which would completely defeat the point of indirect fire support. The FO is located in a position where he can see the target, and he is unlikely to have the same azimuth to the target as the gun. Imagine that he's located in such a place that his azimuth to the target is a right angle compared to the adjusting gun; in such a situation the correction you describe would be reported as "Right" correction (from the FO's POV) but is actually a change in elevation for the gun!

Quote:
It's complex, and requires some mental gymnastics in combat, but long training usually produces adequate results.
It's effectively impossible for most people to do in their heads. Changes in deflection are read from a Plotting Board's vernier scale. Changes in Range are measured from a Plotting Board's range arm.

Quote:
For range, most mortarmen have a pretty good idea of how much a change in elevation of a few mils will alter the point of impact at what range.
This varies by the specific round and how many charges you are using. It's an awful lot of information and not easily memorized. Nobody I have ever met had ever attempted to memorize the firing tables.
Quote:
For more precise work, every set of mortar shells will have a range card, showing this information at various ranges & elevations.
Mortar shells come with Abbreviated Firing Tables (called "Whiz-Wheels") but their use is not preferred except for firing in direct lay. Instead a much more accurate big book of tables called the Tabular Firing Tables is used for most fires.
Quote:
You have to correct, of course, for differences in elevation between yourself & the target,
Yes, this is a mathematical correction (called the "Vertical Adjustment") that gets applied to the first plot. Afterwards it remains in effect, because you are adjusting from that first plot.
Quote:
wind, humidity,
This is called "MET data" and is largely not used in mortars, but rather just assumed to be one of the factors that adjustment takes care of.
Quote:
and, if at enough range, the rotation of the earth.
For weapons with mortar ranges this is ignorable.

Quote:
Example -- the observer says "Left fifty yards, down sixty." Mr. Mortarman says to himself (in those days, always himself) "At eight hundred yards that's 62.5 mils.
Again this wouldn't take into account the difference between the FO's position relative to the target.
Quote:
So he adjusts the dial sight on the mortar tube 62.5 mils to the right (which moves the barrel to the left). He then turns the traversing crank and re-aligns the sight on the aiming stake. Now he's fixed for azimuth.
If it's a small deflection correction, this is correct. Large corrections require moving the bipods.
Quote:
Crank, crank on the elevating handle until the bubble comes level again. Then either tell the observer "Round on the way!" or simply drop-shoot the round and assume Joe Observer knows the sound of a round departing the tube.
"Shot, over" to which the Observer responds "Shot, out", followed by "Splash, over" to which the observer responds "Splash, out" or "Round Unobserved, Repeat, out" (which incidentally is why you use "Say Again" in the radio; "Repeat" means shoot again with the same data).
Quote:
I'd expect that a good mortarman would accomplish all this in a fraction of the time it takes me to tell it.
I was, I am told (by several Battalion Gunners; I also graduated with Honors from FDC school (with I was told a score only a few points short of the record)), very good at what I did, and I couldn't do it the way you describe it.

It's also very difficult (and physically demanding) to be the Gunner or A-Gunner on a mortar. It would be nearly impossible to do either job and the FDC's job at the same time and provide fires in a timely manner. There's a reason these are not just different jobs, they are considered two of the three separate elements of indirect fire (the third is the observer).

Last edited by sir_pudding; 07-17-2014 at 09:26 PM.
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Old 07-15-2014, 09:38 AM   #27
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

There has to be some middle ground. Extremely light mortars such as this one are meant to be deployed and fired almost on the run. Rheinmetall, the current manufacturer, had videos online a while back that illustrated it in use. A man appeared to run up, plonk the thing on the ground, pop a bunch of rounds at targets 300 to 600 meters away, and correct fire entirely on feedback from another guy. That might be manufacturer hype . . . I really don't know. But that's the only kind of mortar fire I've ever used in my campaigns, since any mortar heavy enough not to be a personal weapon in a really light squad of irregulars isn't on the menu for the sorts of adventures I run.
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Old 07-15-2014, 10:00 AM   #28
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

If the observer, gun, and target are approximately colinear, then the Cartesian to polar problem is pretty much as simple as fredtheobviouspseudonym suggested. Normally that can't be assumed, of course, but if the mortar is a squad (or adventuring party)-level asset it might be used that way.
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Old 07-15-2014, 10:22 AM   #29
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

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Originally Posted by Ulzgoroth View Post

If the observer, gun, and target are approximately colinear, then the Cartesian to polar problem is pretty much as simple as fredtheobviouspseudonym suggested. Normally that can't be assumed, of course, but if the mortar is a squad (or adventuring party)-level asset it might be used that way.
I've never run an adventure where that wasn't the case for a 51mm to 60mm infantry mortar. As I said, the observer is just ahead of the mortarman; he might be prone at the summit with the mortar set up literally at his heels on the reverse slope, like this:
X

















--O--
M

Where X is the target, O is the observer, the dashes indicate a ridgeline, and M is the mortarman. The observer is still needed because the mortarman wants to remain in defilade to avoid having his head blown off, and can't easily operate a mortar while prone and unmoving. The prone, stationary, camouflaged observer effectively serves as an aiming periscope, but since the mortarman is relying on relayed targeting information, the skill is still Artillery, not Gunner.

I have no idea how common that arrangement is, but it doesn't seem unrealistic, and it's also consistent with how a tiny team of irregulars might operate.
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Old 07-15-2014, 11:19 AM   #30
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Default Re: [Basic] Skill of the week: Artillery (and Forward Observer)

If it helps, the old British 2" mortar was pretty much aimed by dead reckoning - you lined it up at the target, judged the distance and set the angle of the barrel by a combination of judgement and guesswork. You then fired a bomb and adjusted for fall of shot - but then you only had a range of about 500 yards and weren't likely to be using much in the way of forward observation.

Added historical trivia:
First account of observed indirect fire that I can find occurs during the defence of Hougoumont in the Battle of Waterloo where a battery of the Royal Horse Artillery fired an indirect Shrapnel barrage against advancing French troops using corrections given by the commander of an adjacent battery with a direct line of sight.

Also, IIRC, Naval gunnery observation was quite a big deal in WW2 (as per occurences upthread) - the USN and RN were pioneers in developing fire control shore parties and thus accquired capabilites above and beyond those of other nations.
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