Artillery Fire Direction Calculations

[DKTanker]

From your Grafenwher shoots -- do you recall the range and contrast in altitude between yourself and that last target – was the altitude difference less than 30m, 100m, 200m?

Less than 100m, possibly less than 30m. This wouldn't be the first time I wish I'd saved my 1:50,000 maps of Graf.

 

Also with the early M60 and M48A5, when doing say a HEP shoot that is beyond 4000m do you have to use the quadrant elevation to establish the correct superelevation?   I guess my question is at what range is the ballistic computer no longer going to apply superelevation?

The ballistic computer is good for SE out to 4400 meters. Beyond that the QE or Gunners Quadrant is required.

Edited May 21, 2006 by DKTanker

[jwduquette1]

Thanks again Dave.

[jwduquette1]

This is my picture. Maybe it’s worth a thousand words. Maybe it’s only worth one head scratch and one NY raspberry.

 

 

The trajectory is identical in every case – its been rotated about 125-mils for the second to last SI input figure. Fairly extended range shot. Target is initially at the same elevation as the shooter – so superelevation would in essence be equal to QE and site angle is zero. Next picture is a contrast in altitude of about 100m.

 

From Dave’s Grafenwher description the SI isn’t really being ignored even for a less than 30m to 100m contrast in altitude. More accurately a bit of Kentucky Windage is being employed resulting in an estimated SI being shlocked into the solution by the gunner. Moreover the gunner aims at the top of the target rather than center of mass to compensate for the slight contrast in altitude between shooter and target – that’s an SI angle. But as the targets altitude difference becomes greater and greater, and the range becomes greater and greater the estimated SI or the “windage SI” becomes bigger and bigger. I’d probably not be going out on a limb to say the potential for error in the windage guesstimated SI becomes greater and greater and the probability of a first round hit goes into the shitter. With a 500m contrast in altitude, and for this particular trajectory, you’re no longer aiming at the top of the target, you’re aiming way up in the sky above the top of target – well over 125-mils above the top of the target. I suppose you could still try to windage the SI, or you can use the quadrant elevation or the gunner’s quadrant to determine the SI – they are right there – why not use um. Or as Nigel indicated you can Neanderthal the SI in by shooting a bunch of shells until you have the proper elevation setting. In each of these three modes SI isn’t really being ignored. You’re either trying to guess what it is; or you’re shooting and elevating and shooting and elevating until the gun has the proper SI; or you can simply use your QE to accurately determine SI. I mean, if I’m really in a situation where I have to shoot HEP at ranges in excess of 4000m, and there are even minor altitude contrasts involved, why wouldn’t I take a few seconds and use the quadrant elevation to accurately determine SI? This might save me some ammunition.

 

The last picture represents the same shooter target relationship. Except now there’s a blob of terrain in the way and the shooter can’t see the target – now I’m back on topic with indirect fire and FDC calculations and effects of target elevation. How does the FDC determine the final QE for his gun\guns? Does he use Kentucky Windage and aim for the top of a target he can’t see. Does he shoot a bunch of shells and let the FO walk the bursts onto the target? Does he look at a map, plop a target pin into the presumed target location and read off the altitude at the presumed target location -- subtract his altitude in order to determine VI. Knowing horizontal range and VI he can now calculate SI. This than brings me full circle to my original question – post #22 of this thread:

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=320932

 

If you read what I originally said, my very brief foray into SI was not intended to sideline the thread into a discussion on direct fire. Simply put, what I said was that SI is very easy to determine if the shooter can see the target. He can use his quadrant elevation or the gunner’s quadrant and determine SI fairly accurately (Or he can try some windage guesstimate and fire and adjust -- fire and adjust -- fire and adjust -- till he has in fact input the right SI adjustment into his guns superelevation).

 

The topic of your thread is indicated as: “Artillery Fire Direction Calculations, Target Elevation Effects”. Do FDCs use Kentucky Windage to account for contrasts in altitude between shooter and target? Of course not. They can’t ignore SI. The question is than if I put a blob of terrain between me and the target but keep everything else the same, why is SI suddenly so important? I can ignore SI for direct fire, but I can’t ignore it for indirect fire? That really doesn’t make sense.

 

The second portion of my original question was what I was really interested in. Everything else is a major sidetrack. Lets assume the FO has to walk fire onto a target cause his original target location is not correct. The final FFE location from a shoot will become a reference point or concentration number for future fires. The FO keeps that in his logs. Concentration 304, or whatever. Do you as the FDC shoot the original assumed target position for that particular concentration number if another call for fire occurs for the same spot? Or is the actual target location\target pin replotted based upon the sensings made by the FO? In other words, is that concentration number now a function of the final QE and deflection settings for the FFE; or is it the original QE and deflection settings that were required to hit the presumed location of the target? I would hope the answer is the former case, otherwise everytime that concentration number is used for future fires, the FO will have to walk the fire back onto the actual target location from the old presumed target location. Same again if multiple batteries or mutliple battalions are to be directed onto a target. Lets say a single gun from one battery is initially used for adjusting the fire onto the target. Do the rest of the batteries rely upon the presumed target location for determining their own unique QE and deflection solutions; or is a reploted solution determined based upon the adjusting rounds? I think the later.

[nigelfe]

Er, it's called non-rigidity of the trajectory, and the same term is used by the US Army. What you call SI is actually Angle of Sight (A of S), and this term is also used by the US Army (it's in various STANAGs and QSTAGs not to mention FMs). You'll find it all explained on my web site on the 'Basics of Gunnery' page.

 

However, QE has 2 components, TE and A of S. Ignoring computer methods, manual calcualtions always started with the horizontal distance. The resultant TE was then tilted by the A of S to give QE. However, the horizontal distance is not the same as the hypoteneuse (slope) distance, the latter is greater. Therefore the calculations include a correction for non-rigidity of the trajectory, the exact amount depends on the diff Ht and angle of descent (or fall), which varies with range, charge and MV.

 

Non rigidity started being applied in WW1, although in the BEF it was only for airburst ranging.

[jwduquette1]

Er, it's called non-rigidity of the trajectory, and the same term is used by the US Army.  What you call SI is actually Angle of Sight (A of S), and this term is also used by the US Army (it's in various STANAGs and QSTAGs not to mention FMs).  You'll find it all explained on my web site on the 'Basics of Gunnery' page.

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Nigel:

 

Complenentary site angle is the nomenclature used in the US Army -- not nonrigidity. As I have already said, it is a function of SI. SI is not CAS -- CAS is a function of SI.

 

See my post 35.

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=321478

 

"So if you’re interested in the figuring out what VI is, it's only because you’re trying to determine the SI -- whether you realize it or not. Final Quadrant Elevation is SI plus the adjusted elevation plus the complementary angle of site:

 

And my post 39

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=321543

 

"Adjusted Elevation (adj EL) represents the horizontal range setting corrected for various non-standard conditions -- powder temp, air temp, rotation of the frickin’ earth for gods sake, blah blah blah. The complimentary site angle is an adjustment to QE based upon the site angle (SI)."[/I]

 

My post 40

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=321544

 

"For example, in a previous post I indicated that we here in the US call the correction for the “non-rigidity of trajectory” the “complementary angle of site” – or the “CAS”. The British on the other hand prefer something much more complex and mystical. They refer to the correction for “non rigidity of trajectory” as the – uhh -- well – they call it the “non-rigidity correction”. Go figure?"

 

And see the picture I posted from FM6-40:

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=320932

 

And my post 26 describing how CAS is fairly small and not so important in high velocity direct fire:

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=321145

 

For long range “direct” fire The SI angle is rather crucial when target and shooter are at substantially different altitudes. We just had an in depth on the subject of long range, direct HEP fire on another thread. What has a negligible effect is the complementary angle of site -- particularly for higher velocity guns. But this is a side track. My question is establishing SI in indirect fire.

 

Also see the firing tables I posted that disscuss how to determine CAS based upon the SI.

 

http://63.99.108.76/forums/index.php?showt...ndpost&p=321543

 

Regards

JD

Edited May 22, 2006 by jwduquette1

[jwduquette1]

This is the nomenclature employed in the most recent edition of FM6-40 -- take particular note of the elements of trajectory figure. Something I posted twice before on this thread.

 

 

The above set of snippets represents the nomenclature I have been running with on this thread. I can only assume that the source of your confusion in your last post is in your trying to transpose UK artillery nomenclature into USA nomenclature. If you go back through my previous posts it should be clear what is being disscussed.

 

The angle of site SI is in essence the vertical angle between the horizontal plane and the line of sight to the target.

 

AS I have said in a number of previous posts, the complementary angle of site "CAS" is a correction for nonrigidity. It's added or subtracted (target is higher or lower) when there is a contrast in altitude between target and shooter -- this accounts for nonrigidity of trajectory. It is a multiple of SI -- i.e. you multiple a correction factor (the CSF) times SI to get CAS. See 105mm Howitzer Firing tables I have already posted on page 2. I highlighted the CSF columns -- col 12 & 13.

 

The adjusted elevation "ADJ EL" is the superelevation for a particular horizontal range corrected for powder temperature, atmospheric conditions, curvature of the earth, barrel wear, etc etc.

 

The final quadrant elevation "QE", or the final elevation for the shoot -- as I have already said in a previous post -- is:

 

QE = (ADJ EL + CAS) + SI

 

Where CAS = SI x CSF -- Using a bit of simple algebra, the above expression can be rewritten as:

 

QE = (ADJ EL + (SI x CSF)) +SI

 

This is why I said sometime back that if you ignore SI in a shoot involving contrasts in altititude, you are in essense saying that SI=ZERO and therefore CAS = ZERO.

Edited May 22, 2006 by jwduquette1

[nigelfe]

Complenentary site angle is the nomenclature used in the US Army -- not nonrigidity.  As I have already said, it is a function of SI. SI is not CAS -- CAS is a function of SI. 

 

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Apologies, I checked and found I was looking at a Canadian document referring to non-rig, I'm getting confused all N Americans are so similar :-)

 

Non rigidity is a function of 3 things, not just 1 - range, MV and angle of sight. As I previously said the first 2 determine angle of descent (what I believe is called angle of fall in the US). It's just not possible to determine the correction for non rigidity of the trajectory from either the angle of sight or the diff Ht alone. The diagrams shown above are also misleading because thay show the trajectory as parabolic, poetic licence that can confuse.

 

I think the reason the Brits make no mention of 'complimentary angle of sight' in their terminology is for excellant reasons. Until digital computers appeared they avoided, whenever possible, ordering QEs to guns by using calibrating sights or gun rules. This meant they ordered a range to the guns and true A of S seperately (although historically they'd leave it at zero if they were ranging and diff Ht was small).

 

This of course was different from the slower methods used by the US where a QE always had to be calculated for each gun then order to it, since QE was being calculated I guess it made some sense to call the non-rigidity correction CAS, but its equally valid to see it as a correction to range.

[jwduquette1]

Apologies, I checked and found I was looking at a Canadian document referring to non-rig,  I'm getting confused all N Americans are so similar :-)

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I had assumed the Canadian Artillery Arm – at least in WWII – employed British doctrine.

 

Non rigidity is a function of 3 things, not just 1 - range, MV and angle of sight.  As I previously said the first 2 determine angle of descent (what I believe is called angle of fall in the US).  It's just not possible to determine the correction for non rigidity of the trajectory from either the angle of sight or the diff Ht alone. The diagrams shown above are also misleading because thay show the trajectory as parabolic, poetic licence that can confuse.

324534[/snapback]

 

There is a CSF factor for each horizontal range -- sometimes it's zero like for shorter ranges and higher velocities. But it will also vary with charge – i.e. MV. See my post with the attached range tables for the 105mm Howitzer. It’s really very simple. But again I have already discussed this in a previous post.

 

I think the reason the Brits make no mention of 'complimentary angle of sight' in their terminology is for excellant reasons.  Until digital computers appeared they avoided, whenever possible, ordering QEs to guns by using calibrating sights or gun rules.  This meant they ordered a range to the guns and true A of S seperately (although historically they'd leave it at zero if they were ranging and diff Ht was small).

 

This of course was different from the slower methods used by the US where a QE always had to be calculated for each gun then order to it, since QE was being calculated I guess it made some sense to call the non-rigidity correction CAS, but its equally valid to see it as a correction to range.

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I’m not sure I get this last bit. Are you saying British Artillerists didn’t make corrections for non-rigidity until micro-computers came along?

[nigelfe]

I had assumed the Canadian Artillery Arm – at least in WWII – employed British doctrine.

There is a CSF factor for each horizontal range -- sometimes it's zero like for shorter ranges and higher velocities.  But it will also vary with charge – i.e. MV. See my post with the attached range tables for the 105mm Howitzer.  It’s really very simple.  But again I have already discussed this in a previous post. 

I’m not sure I get this last bit.  Are you saying British Artillerists didn’t make corrections for non-rigidity until micro-computers came along?

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The Cdn ref I found was a modern one, unfortunately I don't have access to the TFT STANAG nor immediate access to a conforming UK FT, the point being that IIRC they don't refer to CAS but to NR. So I'll avoid accusing the US of breaking agreements until I have evidence :-) However, having managed to magnify the FM 6-40 pics to readable size I find a reference to 'nonrigidity' (pg 3-13 (e)) and on pg 7-19 j another TFT STANAG non compliance - it's not called 'max ordinate' the correct term is 'vertex'! Tut tut, what's the IG doing, asleep on the job? Perhaps its a very old edn of FM 6-40.

 

Pg 6-36 is trying to explain what I would call ARFAS and not doing it very well.

 

CSF is one way of determining the non rigidity correction, the point of course is that in FTs the CSF is tabulated against the range (in each charge section of the book) and reflects the angle of descent at that range and charge (at standard MV). Is this the source of confusion?

 

Until forced to use TFTs by NATO the Brits used a graph in RTs for non rig which is quicker than lookup and multiplication. However, Ft Sill seems to have had an aversion to graphs in FTs.

 

One question is when the calculation is done in the manual computing process, does it use map range or range with met and other corrections applied including MV variation from standard? For maximum accuracy the non rigidity/CAS needs to be the last correction added and the range it's looked up at in FTs includes all other corrections. Of course calculating it for each gun's MV is a bit OTT, so using a mean is reasonable.

 

I don't actually think the explanation of non rig copied from FM 6-40 is very clear, I think the graphic on my web site is rather better!

 

Brit arty started using NR in WW1 and have continued ever since, however, they have not always used it (or met) for observed shooting because they took the view that it was quicker to use the gun as a range finder, (speed was also the reason for ranging on BT not OT, again it cut down the CP work). Predicted fire was, of course a different matter but QE was only calculated in the CP if they had to use quadrant laying. Normally they just calculated the range and each gun's sight corrected it for the gun's MV and converted it to TE (A of S was set directly on the sight clino). In prediction non rig was applied as a correction to range not to QE or A of S.

[jwduquette1]

…However, having managed to magnify the FM 6-40 pics to readable size I find a reference to 'nonrigidity' (pg 3-13 (e)) and on pg 7-19 j another TFT STANAG non compliance - it's not called 'max ordinate' the correct term is 'vertex'!  Tut tut, what's the IG doing, asleep on the job?  Perhaps its a very old edn of FM 6-40.

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Click on the postage stamp image. Read the text above the image when the Image-Shack page opens. It will say if the image is in a reduced size. If it’s reduced click the image again and it will magically enlarge.

 

CSF is one way of determining the non rigidity correction, the point of course is that in FTs the CSF is tabulated against the range (in each charge section of the book) and reflects the angle of descent at that range and charge (at standard MV).  Is this the source of confusion?

324976[/snapback]

 

Again, this has already been explained in a previous post.

 

Until forced to use TFTs by NATO the Brits used a graph in RTs for non rig which is quicker than lookup and multiplication.  However, Ft Sill seems to have had an aversion to graphs in FTs

324976[/snapback]

 

 

The British were using firing tables – “Range Tables” -- way back in WWI. Call um’ what you want, they are the same things as firing tables or schusstafeln. RN was using “range tables” prior to WWI.

 

As to non-rigidity, the British used either tabular or graphical solutions for determining non-rigidity – way before NATO was ever invented. Not sure how the graphical method is easier than simply reading a CSF multiplier off a table. But to each his own. Probably why British range tables include both graphical and tabular methods.

 

25-pdr HE (Streamline) 1st Charge, range tables – nonrigidity correction table & nonrigidity graphical.

 

 

Edited May 24, 2006 by jwduquette1

[nigelfe]

Actually previous posts demostrate a certain amount of inconsistency and confusion. I'll recap what I've been saying all long.

 

1. The US uses the term 'nonrigidity' and, it seems from online US glossaries, the term 'correction for nonrigidity' . For reasons that no doubt seemed a good idea at the time 'correction for nonrigidity' is also called 'complimentary angle of sight' in US, probably because this is the way it is applied due to the US ordering angular elevations (QE) to the guns instead of ranges.

 

2. Non rigidity is the name for the effect when a horizontal range is canted by the angle of site to engage a target with same horizontal coordinates. Because the slant range is longer than the horizonalt range and additional correction is required.

 

3. The size of the correction for non rigidity is a function of the height of the target above the horizontal plane and the shell's Angle of Descent (fall for US). A of D is itself a function of MV and range gun to target.

 

4. The US calculates the correction for NR by multiplying a factor given in FTs by the Angle of Sight (or site).

 

5. UK traditionally used range correction read directly from the RTs (no multiplication) and from the 1930s these were a graph, from the early 1950s these graphs came in two types, one for prediction and one for reduction (ARFAS). At this time the graphs were also changed to enable the data to be read at the mean MV of the guns for the particular charge. This gave a small (usually) improvement in accuracy. UK also changed procedures at this time to apply NR to 'Predicted Horizontal Range to give Predicted Range, previously they don't seem to have worried too much about the order of applying corrections to produce Predicted Range.

 

6. It's not (yet) been revealed what other armies do. I'd hazard a guess the French use the US approach because US gunnery is basically copied from them (it goes back to 1917 when the FR instructed the US on the mysteries of 'modern' gunnery.)

 

7. The adoption of TFTs (NATO STANAG 4119) led to some changes in US FTs and the UK ditching RTs (which didn't matter too much because by the time a UK FT appeared they had 2 FACE per bty).

 

8. When you think about how computers calculate a trajectory you realise that it sorts out various minor errors inherent in manual methods.

 

9. Pre WW1 arty RTs had no data for correcting for non standard conditions, although they did include Drift.

 

10. Pages from 25 pr RTs can be seen on my web site.

[starkweatherr]

From Dave’s Grafenwher description the SI isn’t really being ignored even for a less than 30m to 100m contrast in altitude.  More accurately a bit of Kentucky Windage is being employed resulting in an estimated SI being shlocked into the solution by the gunner.  Moreover the gunner aims at the top of the target rather than center of mass to compensate for the slight contrast in altitude between shooter and target – that’s an SI angle. 

 

I think I mentioned this before. Its the way we did it for direct fire.

 

But as the targets altitude difference becomes greater and greater, and the range becomes greater and greater the estimated SI or the “windage SI” becomes bigger and bigger.  I’d probably not be going out on a limb to say the potential for error in the windage guesstimated SI becomes greater and greater and the probability of a first round hit goes into the shitter.  With a 500m contrast in altitude, and for this particular trajectory, you’re no longer aiming at the top of the target, you’re aiming way up in the sky above the top of target – well over 125-mils above the top of the target. 

 

I think that you would just have to fire and adjust. First round hit may not be an issue becuase he has the same problem, in reverse. Then again, if its a Soviet tank, and its above you, it probably can't depress far enough to engage you unless it is on a downhill slope.

 

 

As I understand it, from FM 23-90, once a target is engaged successfully, its the same as a registration point, and left on the board, but stripped of corrections for Vertical Angle. I didn't really understand the explanation for that.

 

What I meant about the correction applied by the ballistic computer is that, with your sights on the target part of the angle has already been calculated. I think that, on the drawing, there is an SI above the gun to target direct line and another angle SI below that line. Due to the trajectory of a tank round, that angle might not be very large. I still haven't been able to find a firing table, but how much does a tank round drop in 4000 meters if fired horizontally? You aren't going to get an accurate solution just by adding the extra angle. I would suggest that a first round hit will be a matter of luck, but see above.

 

A howitzer firing direct fire is a different matter because the projectile doesn't go as fast and would have a lot larger drop at 4000 meters than a tank round, but they also have the equipment necessary for calculating the required adjustment.

[jwduquette1]

Due to the trajectory of a tank round, that angle might not be very large. I still haven't been able to find a firing table, but how much does a tank round drop in 4000 meters if fired horizontally?

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A round fired horizontally will only drop the height between muzzle and the ground. So if the main gun on say an M48A5 is perfectly level, the round will drop – what – about 6 or 6.5 ft. No service ammunition fired from the 105mm M68 gun that I know of will make it even close to 4000m if fired from a perfectly level gun over level ground.

 

I assume what you’re asking is how much does it drop if the appropriate super-elevation is applied for the range of interest? The 105mm M68 gun firing M393A1 HEP Max ordinate for a range of 4000m range is ~139.6m. So the round drops a considerable distance for a horizontal range of 4000m.

 

105mm M2A1 or M4 howitzer using charge-7 firing M1 HE at a range of 4000m -- the max ordinate is ~122.2m. Using charge-2 the max ordinate is 552m for the same range. So it’s also dropping a fair bit -- particularly at lower charges.

 

You aren't going to get an accurate solution just by adding the extra angle. I would suggest that a first round hit will be a matter of luck, but see above.

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It depends. If you look at an FT for say a 105mm howitzer, you see that at closer ranges there is no modification for CAS. The CSF is zero – so QE = adjEL + SI. (again CAS = SI x CSF). Moreover, the nonrigidity effects are small enough that they don’t seemingly matter for the final QE. Same again for very high velocity projectiles. You’ll notice again from examination of 105mm howitzer firing tables that for higher charge numbers the range at which the addition of a CAS elevation to the QE elevation occurs further and further down range.

 

For example 105mm M2A1 or M4 howitzer firing charge-3 you start seeing a CAS adjustment kicking in for a horizontal range of only about 800meters. The CSF gets progressively larger with range. So CSF is about +0.01 at 800m and rises to +1.46 at 5100m (target at a higher altitude – hence the positive sign on the CSF). For Charge-7 you don’t see a CSF start kicking in until a horizontal range of about 3100m – CSF +0.01. For charge-7 the CSF =+1.68 at a range of 12000m.

Edited May 26, 2006 by jwduquette1

[jwduquette1]

As to not being able to find FTs -- what are you looking for? Mortar or Howitzer FTs? I'd be happy to mail you a set of photo copies for one or the other if it will assist with your project.

[starkweatherr]

As to not being able to find FTs -- what are you looking for?  Mortar or Howitzer FTs?  I'd be happy to mail you a set of photo copies for one or the other if it will assist with your project.

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This really blows. I wrote a couple of paragraphs and got dumped before it was actually posted.

 

I would like a copy of FT 105-A-2. I have a full set of M-60A3 TMs that I am scanning and would like to add that. When I Google for FT 105-A-2 I keep getting hits on new strains of asparagus from Nepal.

 

If you have a known range to target of 5100 meters, I would suggest that you could get by with setting up the M-105 so that the target is sitting on the 4000 meter line, and figure the extra superelevation from the firing tables. If the firing table has a column for required elevation to raise the strike of the round a given distance, use that, or . . .

 

For VA/SI at that range, you could use the mil relationship. If the target is five meters above your elevation, and I'm not sure how you would know that, the adjustment would be 0.98 mil of elevation for a range of 5100 meters. REMEMBER: that is the trignonmetric solution and will only be accurate if you are firing a laser. But I don't see what else you would be able to do in a reasonable period of time and with the resources you would have available in a tank.

Edited May 26, 2006 by starkweatherr

[nigelfe]

There's a fundamental difference between what tanks do and what arty does.

 

Arty fires at coordinates from a surveyed position, calculates the horizontal range then corrects that range by calculation or adjustment to tilt it and find the slant range and appropriate QE. In the calculation there are two components that we've discussed ad nauseam.

 

Tanks aim directly at targets, they find the slant range straight off whether they range find by rg MG, optical RF or laser RF. And by aiming at the target it is already taking angle of sight into account.

 

Tanks only need to calculate A of S and NR corrn if they are playing at being artillery. If that's what you want to do (my advice forget it arty does it better), then you need to think in terms of a proj with similar ballistic coefficient to an arty shell and roughly the same MV, taken together they should give a similar trajectory and hence a similar correction for NR at the same range, which you will indeed find in an FT for an arty shell that matches. So first question, what's the ballistic coefficient, second question what's the coefficient of the arty shell you reckon is a match?

 

The only residual issues are if diff Ht is so great that it puts the traj thru an atmosphere well above the surface, and since tanks don't have the meteor data anyway its not worth breaking into a sweat over. Or that the traj height and shape of the ground is such that you get gravitional distortion on the proj. At the mickey mouse ranges involving tank gunnery I wouldn't get steamed up about this either.

[jwduquette1]

This really blows. I wrote a couple of paragraphs and got dumped before it was actually posted.

 

I would like a copy of FT 105-A-2. I have a full set of M-60A3 TMs that I am scanning and would like to add that. When I Google for FT 105-A-2 I keep getting hits on new strains of asparagus from Nepal.

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I don’t have FT 105-A-2 nor do I know what it is for. Was this the early version of A-3? Are you looking for tables for the 105mm M68 gun? Or are you looking for FTs for a howitzer or the like?

 

If you have a known range to target of 5100 meters, I would suggest that you could get by with setting up the M-105 so that the target is sitting on the 4000 meter line, and figure the extra superelevation from the firing tables. If the firing table has a column for required elevation to raise the strike of the round a given distance, use that, or...

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I have never had to do a long range shoot with the M68 gun, however the methodology was explained to me by Marine tanker gunnery sergeant. I think he did his time in M48’s and M60’s. Anyway the methodology is not really too different from direct lay with an artillery piece. For say an M48A5 the gunner actually uses the boresight cross on the 105D and the quadrant elevation to establish the SI. You set the boresight cross of the 105D on the target than re-level the quadrant elevation to determine your SI.

 

You can than use either the gunner’s quadrant or the quadrant elevation to establish the final superelevation for the shoot – analogous to the final QE. The final superelevation is than the superelevation for the correct horizontal range plus (or minus) the SI.

 

Any HEP shot over about 3200m won’t even be visible to the gunner in the 105D – i.e. it’s out of the field of view of this telescope – particularly if there is a large SI involved. Remember that the HEP reticle on the 105D only has range increament lines up to 3200m – that’s way at the bottom of the reticle. There is a bit more field of vision beyond that last 3200m range line but there aren’t any graduations beyond 3200m. So maybe you can still see the target out to 3400m(?) or 3600m(?) at the extreme bottom of the 105D telescope picture -- beyond the bottom most HEP range line.

 

For longer ranged direct lay of say a Howitzer on a target above or below the guns altitude, you would place the line of sight parallel to the axis of the bore. Place the intersection of the horizontal and vertical hairs of the panoramic telescope on the target. Measure the elevation of the tube with the gunner’s quadrant. The angle of elevation of the tube is the angle of site – your SI. Add the SI to the firing table elevation corresponding to the correct horizontal range to the target and appropriate charge to be fired – this is your QE for the shoot.

[jwduquette1]

Tanks aim directly at targets, they find the slant range straight off whether they range find by rg MG, optical RF or laser RF.  And by aiming at the target it is already taking angle of sight into account. 

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Not for a HEP shoot out to 5100m. A ballistic reticle -- particularly in the case of HEP -- is only gonna take you so far before you run out of range lines. For example the M-105D telescope is graduated to 3200m for HEP. But HEP can certainly be fired out to much longer ranges -- direct or indirect. So for long range HEP shoots vs. targets at a differing altitude you would need to determine the SI and input QE as EL + SI via either the quadrant elevation or gunners quadrant.

[starkweatherr]

Tanks only need to calculate A of S and NR corrn if they are playing at being artillery.  If that's what you want to do (my advice forget it arty does it better), then you need to think in terms of a proj with similar ballistic coefficient to an arty shell and roughly the same MV, taken together they should give a similar trajectory and hence a similar correction for NR at the same range, which you will indeed find in an FT for an arty shell that matches.  So first question, what's the ballistic coefficient, second question what's the coefficient of the arty shell you reckon is a match?

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The US did use tanks as artillery in Korea. I'm not sure that they have done it since. They parked the tanks on dirt ramps and I believe that the shoots were controlled by arty personnel. You're right, though. Artillery is better at it.

 

Firing tables for tank rounds are available. FT 105-A-2, according to TM 9-2350-257-10-2 this is the firing table set for the 105mm M-68 Gun/Cannon as used in the M-60A3. I'm pretty sure you're right that computing MET data for a tank shoot would be unusual, but it should have all of the other data that you would expect to find in any other firing table for a fixed charge artillery piece, if there is such a thing any more.

 

JW, since I wasn't really interested in that part of it, I didn't check to see what the max range on the M-105D HEP reticle was. Sorry. Next, unfortunately, I wouldn't accept much gunnery advice from the Marines. I was in the Marines for 12 years, although I was a TOW gunner then instead of a tank gunner. Anyway, I've seen them shoot. It wasn't pretty.

 

If you start with the boresight cross in the M-105D, you lose the aim off needed by the spin of the round. If you notice, the vertical part of the reticle leans to the right at the bottom to allow for the aim off due to the spin. It looks like it gets close to five mils aim off at 3000 meters. I would suggest adjusting from the longest range that is available on the reticle to avoid losing this aim off. There may be another way to do it if you use the M-32, but the M-105D is a better sight, in general.

 

You are right that it doesn't make much sense to go past the end of the reticle. What I meant was, lay the 3?00 meter crosshairs on the target and then use the azimuth indicator and the quadrant of elevation, or the more accurate M1A1 to make the final adjustments. The rest is as you said, but don't forget the aim off for the spin.

[nigelfe]

Yes that had been puzzling me, but I thought my memory must be failing. I don't recall any 105 mm How RT/FT (and I've used used 5 different guns L5, M2A2, L13, L118, L119) going anywhere near 5000m for direct fire (ie HESH/HEP). The chances of a hit against a tank are so small at longer ranges you wouldn't want to encourage the gun to open fire by providing data (although L13 had quite a good atk telescope with normal adjustable graticules for range and lead)!

 

The rest of the RT/FT was irrelevant because HESH and IIRC HEP has a very different shape (about 3 crh) compared to the std HE proj (about 10 crh) so the ballistics are totally different. IIRC the weight is less too, this figures because HESH is short range so a lighter shell with higher MV but lower carrying power is OK.

 

While previous tks did have RTs, certainly 20 pr and I think L7 105mm, I've never heard of tanks calibrating, and zeroing achieves something different. I also doubt if they had the means of easily calculating corrections for non-standard conditions even if they could get the data. UK did use tks for indirect fire at the back end of WW2 but my understanding is it was part of the 'pepperpot' phase so it was sprayed around and accuracy wasn't too important.

[jwduquette1]

Yes that had been puzzling me, but I thought my memory must be failing.  I don't recall any 105 mm How RT/FT (and I've used used 5 different guns L5, M2A2, L13, L118, L119) going anywhere near 5000m for direct fire (ie HESH/HEP).  The chances of a hit against a tank are so small at longer ranges you wouldn't want to encourage the gun to open fire by providing data (although L13 had quite a good atk telescope with normal adjustable graticules for range and lead)! 

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Hmm -- my take as well some time back. Yet a number of your own were going on about the great ease of 5000m(+) HESH shots against tanks. It was in reference to a Scots DG Challenger first round hit on a Iraqi T-55 at 5100m (although various accounts put the range as high as 5300m -- other accounts imply APFSDS was used, although this doesnt detract from the ardent insistors' that HESH was employed and that it is extremely accurate at these sorts of ranges). Inherent shot dispersion alone makes such a shot seem nearly impossible. Yet a number of folks that have crewed Chieftains & Challengers and post to this forum claim such a HESH shot wasn’t really an extreme bit of luck at all and can be performed on a regular basis. Seems to me the Israelis up on the Golan were doing accurate direct fire shoots with Centurions up to 8000 to 10000m against dug-in Syrian tanks and earthmoving equipment.

 

Now a 5000m direct fire shot in naval gunnery is considered short range for a 4 or 5-inch gun -- even as far back as WWI. This suggests that the only real limitation in similar ranged shots on the land is direct line of sight and terrain that might block LOS -- as evidenced by the various successful long range direct fire tank shoots that came out of both Desert Storm and OIF.

 

So why exactly are direct fire shoots out to 5000m impossible, but indirect shoots at the same range are possible? At what range are direct fire shoots with HEP or HESH or HE impossible? Is it 3200m – because that’s max range in the M-105D telescope? Is it 2000m? Is it 1500m?

Edited June 1, 2006 by jwduquette1

[jwduquette1]

Sorry. Next, unfortunately, I wouldn't accept much gunnery advice from the Marines.

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On the other hand, are you suggesting I should take tank gunnery advise from guys that dont understand their own site telescopes Sorry -- couldnt resist.

 

As far as the aim off bit -- your talking about drift correction. FT's for the M68 do include drift correction data for long range shoots. The gunner has an azimuth indicator (as you have said) which can be employed to adjust the aim point to compensate for spin induced drift. As to other bits and pieces implied about non-standard conditions, the FTs for the M68 do indeed include corrections for EL for non-standard conditions. But of course if I can arbitrarily ignore SI in these sorts of shoots why would I worry my head about pesky contrasts in non-standard conditions -- ala powder temp, or air temp, etc.

 

I don't have the A-2 firing tables. I have the A-3 tables for the M68. I take it you are no longer interested in FDC calculations and contrasts in elevation? Check your forum email. I sent you an email regarding M68 FT's.

Edited June 1, 2006 by jwduquette1

[nigelfe]

Tanks are designed for direct fire shooting, artillery is not, its strictly a secondary role (if at all). This is reflected in the sights. The ammo has nothing to do with it. That said guns like PzH2000 do have quite a sophisticated direct fire capability and LRF, but most armies have difficulty in justifying such a capability for field artillery.

 

It demonstrates a fundamental lack of understanding to compare HESH from tank with HESH from a field gun. The key difference is the fire control technology, most guns haven't moved on very far from WW2 technology. I don't think tanks were very good at hitting targets at 5000m at that time either! Even the best atk guns with HV shot were hard pressed much above 2500m, and that wouldn't be a moving target.

 

By the same token tanks aren't designed for indirect fire and aren't very good at it - you can start with the rate of barrel wear and the small amount of ammo that is used in direct fire for several obvious reasons (notably physical mobility not firepower mobility). Long range direct fire, enabled by accurate range measurement, lead computing sights and perhaps allowing for low level wind and charge temp are not the same thing as indirect fire.

[DKTanker]

Now a 5000m direct fire shot in naval gunnery is considered short range for a 4 or 5-inch gun -- even as far back as WWI.  This suggests that the only real limitation in similar ranged shots on the land is direct line of sight and terrain that might block LOS -- as evidenced by the various successful long range direct fire tank shoots that came out of both Desert Storm and OIF.

I submit to you that firing at a ship size target at 5,000 meters is in no way comparable to shooting at a tank size target at 5,000 meters. When the navy guys start talking about first round hits, with low MV HE, at 5,000 meters on 2 meter panels, I'll call BS on them too.

[jwduquette1]

I submit to you that firing at a ship size target at 5,000 meters is in no way comparable to shooting at a tank size target at 5,000 meters.  When the navy guys start talking about first round hits, with low MV HE, at 5,000 meters on 2 meter panels, I'll call BS on them too.

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Finally -- I was hoping at some point you were gonna jump into this morass. I'm less interested in the debating tactics going on here, and more interested in what can and can't be done.

 

Common shell and spgr are actually fairly slow moving shells -- particularly back in WWI. Ships -- both target and shooter -- are typically moving as well as pitching, yawing and rolling so while the targets are larger, the task is still fairly difficult. Regardless. Assume for a second you are crewing an artillery piece; Why would indirect fire be any more effective than direct fire -- same range for either mode?

 

Regarding the stories floating about on this forum about tanks accurately shooting HESH at tank sized targets 5km away and consistently getting 1st, 2nd or even 3rd round hits -- in your experiance is this BS?

 

Regards

JD