Steve Jackson Games Forums - View Single Post - [Basic] Skill of the week: Artillery (and Forward Observer)

fredtheobviouspseudonym · 07-14-2014, 04:42 PM

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.

07-14-2014, 04:42 PM	#25
fredtheobviouspseudonym Join Date: May 2007	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.