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Posted: 3/9/2010 4:11:58 PM EDT

I never went to IMPOC so forgive me- what kind of adjustments are built into the calculations when firing from point A at elevation x when the target Point B is at a vastly different elevation, say x+750 ft or more??

I have seen vids and pics of various mortars in action in Afghanistan and the elevation differences must be a factor in the fire mission calculations.

Or am I overthinking it that the computer knows the elevation of the coordinates that you input and makes the calculations accordingly...

Just curious and thanks in advance- I was just a light grunt PL many moons ago...

4073


Link Posted: 3/9/2010 4:14:58 PM EDT
30 years ago we did the calculations manually
Link Posted: 3/9/2010 4:16:31 PM EDT
I honestly don't remember how we allowed for height differences. Of course it was manually done then. I'm sure the computers now take all that into consideration.
Link Posted: 3/9/2010 4:18:24 PM EDT
Link Posted: 3/9/2010 4:19:12 PM EDT
back in the day of plotting boards, If I remember right there was a chart you had to
use, and one for the range to get the charge and then you had fig. angleT.
I never was an FDC guy though
Link Posted: 3/9/2010 4:20:10 PM EDT
[Last Edit: 3/9/2010 4:20:43 PM EDT by ABNAK]
Originally Posted By DK-Prof:
When I used the tiny 60mm, it was all hand-calculated and guesstimates.




I can't recall if there was a factor and/or calculation involved. Spent most of my time as a "gun bunny", not shamming out in FDC!



Link Posted: 3/9/2010 4:21:40 PM EDT
Just keep dropping them in there and walk it into your target...
Link Posted: 3/9/2010 4:22:58 PM EDT
Originally Posted By realwar:
Just keep dropping them in there and walk it into your target...


Sounds good to me!

Link Posted: 3/9/2010 4:25:36 PM EDT
Originally Posted By ABNAK:
Originally Posted By realwar:
Just keep dropping them in there and walk it into your target...


Sounds good to me!



Unless there are friendlies around!!

4073

Link Posted: 3/9/2010 4:27:52 PM EDT
Hell I don't remember how we did it by "hand"
But the MBC can handle it pretty easy.

Monk

ETA...We use the 81mm mortars, the 82mm is an old Soviet block system IIRC.
Link Posted: 3/9/2010 4:28:04 PM EDT
Originally Posted By MFP_4073:
Originally Posted By ABNAK:
Originally Posted By realwar:
Just keep dropping them in there and walk it into your target...


Sounds good to me!



Unless there are friendlies around!!

4073



German Mountain Doctrine would suggest that they move.
Link Posted: 3/9/2010 4:36:43 PM EDT

81 - 82... whatever it takes.



4073
Link Posted: 3/9/2010 4:43:58 PM EDT
You use the ammo data book and correct for "Up" or "Down" height/elevation.
Link Posted: 3/9/2010 4:50:21 PM EDT
[Last Edit: 3/9/2010 4:51:48 PM EDT by dogface_313]
Not a Mortar man, but I am a Red Leg.

What you are talking about is called the "Site factor". With mortar systems unless you are firing in conventional mode, i.e. not direct lay or hand held mode you don't need to calculate site. However if you are firing conventional mode i.e. setting up aiming stakes, Large base plate etc. you will most likely be using an LHMBC Light-weight Hand-Held mortar ballistic computer. One of the first things you do with it is build your firing unit i.e. enter your location and also enter your elevation. You do this yourself, never rely on the computer. When somebody calls for fire depending upon the type of mission they should give you elevation data. Not directly but you normally know where the observer is, if the target is more than a + or - 35 m difference from observer location they are supposed to call in an up/down correction. No matter what, whether they call in a grid mission, polar, or shift you will be able to plot the target location on a map and pull an approximate elevation of a map.

You must remember that unless it is a precision guided munition it is an AREA fire weapon system. The system is only as good as of its components, The observer, the Fire direction center, and the firing unit. This is why first round steel on steel is a rare event and most missions need adjustments.

edit: I forgot to add that Mortar missions by doctrine are always to suppress the enemy, they are not to Neutralize or destroy. Just get those things close enough to keep their head down.
Link Posted: 3/9/2010 4:52:09 PM EDT
[Last Edit: 3/9/2010 4:54:28 PM EDT by The-Bald-Monk]
Here are a couple of things I found on the net.

http://www.mca-marines.org/gazette/oct09-retooling_for_afghanistan.asp
It is generally advisable to take a 60mm mortar on dismounted patrols. Because of their inability to range the adjacent terrain around FOBs, 81mm mortars are frequently of marginal value on anything other than mounted patrols. In such cases attaining 120mm mortars and 105mm howitzers from our Army counterparts is wise. Heavy mortars with their high angles of fire are generally easier to adjust on target in vertical terrain than howitzers, which are characterized by a flatter trajectory.


FM 23-91 MORTAR GUNNERY

14-3. VERTICAL INTERVAL CORRECTION FACTORS

When the mortar position is known to surveyed accuracy and a map is being used, the computer can work with altitude differences and the correction factor for those altitude differences. As noted earlier, the term used for altitude difference is vertical interval (VI).

a. Determination of Vertical Interval. The computer compares the altitude of the mortar position and the altitude of the target being engaged. If the altitude of the target is higher than that of the mortar position, then the VI will be a plus (+); if lower, it will be a minus (-) (Figure 14-10).

Figure 14-10. Altitude correction.

b. Correction for Vertical Interval. Because of the VI, a range correction must be applied to the chart range to obtain the range to be fired (command). The range correction to apply is half of the VI; it is determined to the nearest whole meter.

EXAMPLE
VI = 75 meters
1/2 = 38 meters (altitude [range] correction)

The altitude (range) correction must be 25 meters or more to be applied. The range correction is then added to or subtracted from the chart range. If the target is higher than the mortar, the computer adds the range correction; if lower, the computer subtracts to get the altitude to be fired (command). The altitude correction is applied to every chart range throughout the mission.
NOTE:A VI of less than 50 meters is not used when working with the modified-observed chart.

c. Determination of Vertical Interval for Different Missions. When there is a difference in altitude between the mortar position and the target, a range correction is made. Since the mortar round has a steep angle of fall, corrections are made only when differences of 50 meters or more in altitude exist. The chart range is corrected by one-half the difference in altitude expressed in meters. The correction is added when the target is above the mortar, and subtracted when the target is below the mortar. Difference in altitude can be determined from contour maps, by estimating, or by measuring the angle of sight, and by using the mil-relation formula.

(1) Grid missions. The target is plotted on the map and the altitude determined. If the altitude of the target cannot be determined, then the computer assumes that it is the same as that of the mortars.

(2) Shift missions. The target is assumed to be the same altitude as the point being shifted from unless, in the call for fire, the FO sends a vertical shift (up or down). Therefore, that shift is applied to the point being shifted from, and that is the altitude of the new target.

(3) Polar missions. The altitude of the target is assumed to be the same as that of the FO's position if no vertical shift is given. If one is given, then the computer applies the shift to the FO's altitude, and that is the altitude of the new target. Once the computer has determined the altitude of the target, then it is possible to determine the VI for the mission and, finally, the altitude correction to apply. Remember, VI is the difference in altitude between the mortars and the target.
Link Posted: 3/9/2010 4:53:04 PM EDT
hell, I thought the rounds would just blow up when they hit the dirt, unless you're shooting Illum. or want an air burst?
Link Posted: 3/9/2010 5:51:23 PM EDT
[Last Edit: 3/9/2010 5:54:16 PM EDT by ABNAK]
The-Bald-Monk,

So if there is basically a <50m (maybe 160ft?) difference in elevation between firing point and target point then it is calculated as usual (using the aiming stake setup). If it's >50M then it's half the distance difference (in meters?) than the mortar and target, right? Added or subtracted of course. Good as a refresher for an old mortar maggot!

Given today's GPS systems I'd assume that elevations are *easily* (relative term there) obtained?

I'm not sure if I agree with the assertion that a fixed 81mm mortar (say at a FOB in the boonies) does not have the capability to range targets. In today's modern battlefield the U.S. serviceman *should* have laser capabilities readily available, especially at a semi-permanent FOB-type firing platform from which they would be engaging the enemy.
Link Posted: 3/9/2010 6:14:36 PM EDT
[Last Edit: 3/9/2010 6:15:36 PM EDT by The-Bald-Monk]
Originally Posted By ABNAK:
The-Bald-Monk,

So if there is basically a <50m (maybe 160ft?) difference in elevation between firing point and target point then it is calculated as usual (using the aiming stake setup). If it's >50M then it's half the distance difference (in meters?) than the mortar and target, right? Added or subtracted of course. Good as a refresher for an old mortar maggot!

Given today's GPS systems I'd assume that elevations are *easily* (relative term there) obtained?

I'm not sure if I agree with the assertion that a fixed 81mm mortar (say at a FOB in the boonies) does not have the capability to range targets. In today's modern battlefield the U.S. serviceman *should* have laser capabilities readily available, especially at a semi-permanent FOB-type firing platform from which they would be engaging the enemy.


I think so

As I read it and from what little I can recall if you use VI then your range to target change and that would effect the tube elevation and charge(s) applied to the round.
I was at Camp Lejuene which is flat as pancake so we only used when we went to CAX.
I do recall one time when the Gunny was not happy when we screwed it up on Range 400 and sent a round high on the mountain

GPS can give you the elevation for the gun line and the FO's position but the FO is going to have to guessstimate the target elevation.
Maps and LRF can help with that.

IIRC max effective range of 81mm is 5,700 meters and I think the 120 can range out to 7,200 meters
155mm howitzers are around 14,000 meters

It has been over 10 years since I ran a fire mission and none of the call for fire practice I did at Sgt's Course required us of VI.


Monk
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