Artillery Fire Direction Calculations

[jwduquette1]

I see that my rather long reply has disappeared. Hmmm.

 

For direct fire I think that if any allowance is made for the SI angle at all it would just be a matter of adjusting the position of the cross hairs on the target. If the target is above you, aim at the top, If it is below you, aim at the bottom.

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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.

[jwduquette1]

I also suspect that VI is determined by the firing battery from survey data of the firing site, and the map elevation of the target. This is another thing that wouldn't be important to the FO as long as the spotting rounds hit where he can see them.

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It may not be important to the FO, but I thought your original question regarded FDC calculations?

[jwduquette1]

Until 1950 and the adoption of Target Grid Corrections the British and like minded armies did not use OT, they generally used GT (or BT as it was then known).  Basically it meant the observer had to envisage the line of fire on the ground and this takes a bit more skill than using OT.  Of course in those days the line of fire was mostly reasonably close to over the observers's head.  GT is also the norm for air observers.

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It seems to have been the exact opposite in the US Army -- at least if we are to take the FM6-40s of this period at face value. Both the FM6-40 from June 1945, and the FM6-40 from 1950 indicate the FDC adjusts to maintain bursts on the OT line. To me this seems a simpler operating procedure -- particularly if the firing battery occasionally had to conduct corrections based upon commands from folks that aren’t formally trained FOs or FOOs.

 

Someone on another forum once told me that the in the British Army of WWII only FOOs can do calls for fire. No idea if this was true – I suspect not but I don’t know for certain. In the US Army any soldier who could read a map and had access to a radio could potentially call for artillery fire. It is still this way. To me it makes more sense in the later case to use the OT line, and for the FDC to conduct his adjustments to maintain bursts on the OT line rather than the guy calling for fire trying to envision the BT line...i.e. a soldier who is not trained or only partially trained in calling for artillery fire can easily correct fire based upon his direct line of sight to the target – LEFT, RIGHT, ADD, DROP (or whatever). The same soldier would probably have a much harder time trying to figure out what and where the BT line is and adjust his burst sensing in accordance with the BT line.

Edited May 13, 2006 by jwduquette1

[DKTanker]

The terms are ADD or DROP, and LEFT or RIGHT.

[nitpick] UP and DOWN are perfectly acceptable when adjusting VT and Illumination [/nitpick]

[jwduquette1]

[nitpick] UP and DOWN are perfectly acceptable when adjusting VT and Illumination [/nitpick] 

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Use of "degrees" instead of "mils" by the Soldier or Marine doing the observing is also perfectly acceptable. The FDC is supposed to be able to figure out what a partially or untrained observer means when that observer uses degrees. But again I have never had to observe and adjust indirect fire and therefore have to take the preaching’s of FM6-40 literally.

 

The thing of it is when folks like yourself or Gunny Jake were talking about long range direct tank fire it was very easy for me to pick up any version of FM17-12 and see exactly what it was you two were referring to. I assume I should be able to do the same when someone is talking about indirect artillery fire and FM6-40, but perhaps this isn't the case?

 

Best Regards

JD

[DKTanker]

Use of "degrees" instead of "mils" by the Soldier or Marine doing the observing is also perfectly acceptable.  The FDC is supposed to be able to figure out what a partially or untrained observer means when that observer uses degrees.  But again I have never had to observe and adjust indirect fire and therefore have to take the preaching’s of FM6-40 literally. 

 

The thing of it is when folks like yourself or Gunny Jake were talking about long range direct tank fire it was very easy for me to pick up any version of FM17-12 and see exactly what it was you two were referring to.  I assume I should be able to do the same when someone is talking about indirect artillery fire and FM6-40, but perhaps this isn't the case?

 

Best Regards

JD

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Having only some class room and simulator experience with such things, as I recall the FDC 'figures out' degrees or mils by asking the FO for clarification. Either way the FDC can put one or the other into the computer and get a firing solution and or correction solution.

 

For the US Army, Navy, AF, and USMC, the procedures and terminology are all the same. They may not be able to talk to each other, but when they can, they all speak the same Indirect Conduct of Fire language.

 

I dare say with all the new fangled GLIDs, GPS, Data Links, et al, much has been forgotten or fallen by the wayside. The FO of today points his GLID at a target and shoots his laser. His position, the range to the target, and the azimuth are automatically sent to the FDC and or directly to the guns.

[starkweatherr]

Having only some class room and simulator experience  with such things, as I recall the FDC 'figures out' degrees or mils by asking the FO for clarification.  Either way the FDC can put one or the other into the computer and get a firing solution and or correction solution.

 

For the US Army, Navy, AF, and USMC, the procedures and terminology are all the same.  They may not be able to talk to each other, but when they can, they all speak the same Indirect Conduct of Fire language.

 

I dare say with all the new fangled GLIDs, GPS, Data Links, et al, much has been forgotten or fallen by the wayside.  The FO of today points his GLID at a target and shoots his laser.  His position, the range to the target, and the azimuth are automatically sent to the FDC and or directly to the guns.

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FM 23-90, not sure of the date, still has instruction for manual calculations, although no mention is made of converting degrees to mils. (?) I assume that every one with a radio is supposed to also be issued with a compass that reads out in mils. (I know that I never had one when I carried a radio.) Or remember the magic number 17.7777.

 

JW is right. I'm really only looking at it from the FDCs perspective, and I finally found the answer, at least for US mortars.

 

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

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

 

This is the VI calculated by the FDC from the firing battery to the target and is only used with the first round fired. After that all corrections are based on the FO's input.

 

When registering a new target using Mean Point of Impact, they have to do some very complicated stuff that involves the vertical angles from both FOs (two with M-2 Aiming Circles required, or one or more radar sets for MPI) to the target as well as the VI of the Registration Point, which is not the same as the target. I'm going to have to look at that a lot closer because they picked an example where several of the vertical intervals are 25 meters and I can't figure out which is which right now.

 

The manual says that MPI is only used in low visibility, on featureless terrain, or for re-registration.

 

Also, if not done on the MBC (Mortar Ballistic Computer) the FDC plots on either the M-16 or M-19 plotting board. (The difference is the range scale). Although it is not intuitively obvious how to use one of these, once it is set up figuring corrections based on FO data is as simple as rotating the dial back and forth between the FO's azimuth to the target and the battery azimuth to target. Basically, there is no apparent reason to try to keep the strike of the rounds on the OT line, or any other line, when using the plotting board.

 

When the FO's azimuth is indexed, corrections are Add/Drop Left/Right from the first plot of the target but from his viewpoint as if he were at the center of the board, resulting in a dot on the board. When the dial is rotated back so that the new dot is on a vertical line through the firing battery, the azimuth and range to that dot are read off directly. Pretty clever. It gets a little more complicated if the range to the target is larger than the range from the center of the board, to the edge, so the firing battery is no longer at the center, but not by much.

 

After my sixth preview and fourth edit it is obvious that I didn't explain things very well. If you have any questions, please ask, and I will try to make up something plausible.

 

Now all I need to do is see if there is any difference between mortar procedure and howitzer procedure.

Edited May 13, 2006 by starkweatherr

[nigelfe]

Before an inf or armd soldier can pick up a radio and order arty fire the radio has to be on the right arty freq, in reality not quite so convenient as it sounds. Brit practice was to keep such people off arty nets because they lacked arty comms skills which were essential for keeping the arty system working slickly. Their solution was (and is for voice comms) for the inf/armd guy to talk to the arty observer on the coy/sqn net (Brit FOs have voice comms on both arty and inf/armd nets), the FO then translated what they want into proper arty fire orders (and if he could see the target he totally took over the engagement). It makes training a whole lot simpler and keeps the arty system working slickly. Of course pervasive data networks change this, in effect anybody can launch a CFF msg into the arty system without compromising its efficiency. In the Brit comms system arty fire orders on arty nets use different and more efficient procedures to standard voice comms, but require a higher standard of training.

 

The fundamental difference between Brit and US arty systems is that in the Brit system the FDC doesn't need to exist, it's only used for observers who want more than their SOP or operation specific authority allows. Wihtin their authorty FOs etc give orders to the guns not requests to an FDC, this puts most fire control where it it's needed, alongside the supported arm, not is some arty HQ stuck in the rear and fighting its own private war. Obviouly there are arrangements for deconfliction in case more than one person orders everything at the same time.

 

Traditionally, FOs can always call their own battery, BCs and other nominated observers their regt, other nominated observers the div arty. Other HQs/staffs, notably CB, can also be given authority for engagements without going thru a FC centre. Data comms enable refinement to this, in that allotment authority for any number of guns can be placed where it is best used for a period of time, eg a BC at a inf/armd bn HQ (which is where Brit BCs hang out) can have authority over a corps arty for a (short) period if necessary.

 

The mechanics of shooting with large angle T or whatever are esentially matters for training observers. In WW2 the Brits didn't usually bother about angle of sight for observed fire unless it was very large. If they can see the fall of shot they can adjust it, the tricky bit is interpreting the effects of sloping ground and its relation to the line of fire, this only comes with experience. Using two guns wouldn't (these days) be parallel since adjusting guns are converged by convention. In WW2 they would have been parallel. Of couse the easist solution is to use a LRF and fire a 3 rd group. However, these days various technical advances mean that the opening round is normally close enough for FFE to be effective (providing the observer correctly identified the tgt location!). In Basra 03 the Brits were opening at converged FFE on individual bunkers as ordered by observers.

[starkweatherr]

It's been more than 30 years since I had call for fire training, and I'm sure there have been a lot of changes. An FO with a GPS and laser range finder should be able to put the guns right on target very quickly. I think that manual plotting will still be taught until we learn how to nullify EMP.

 

I have a British friend who was RTO in a Chieftan unit for a while who told me a little about the different radio sets. The years in the military that I didn't spend with combat arms I was a radio technician, so I was interested.

 

I don't know what system was used during Korea, but I'm pretty sure that in WWII the US had different radios for different types of units. By Vietnam, though, the US had a standard set of radios for most ground troops that operated in the 32.00 to 75.95 MHz range. There were different models, but even the man-pack PRC-25/77 used the same frequency range. In a way this was convenient because there was usually a way to have two frequencies preset. One would be unit and the other might be artillery, depending on what the person or vehicle's function was. A company commander usually had a vehicle mounted setup that had buttons for 10 presets and an additional receiver or two. He could only transmit on one frequency at a time, but he could listen to three. In a lot of cases an FO would ride with the CO, and he would probably have a man-pack radio along set to his units frequency.

 

One reason why the US might feel comfortable having someone with only a few hours training call for fire is that the typical fire command has a lot of default values. For instance, unless the FO specifically asks for something else, the FDC assumes HE Quick.

 

You also mentioned that British FOs didn't really need an FDC. Considering all of the calculations the FDC has to do to allow for propellant temperature, MET report data, and some other wierd things, how do the British do that? If you don't use the plotting board and do use the Mortar Ballistic Computer, there are still some calculations that need to be done. Can you give me a link to a site that explains the British system? I have enough questions that it seems unlikely you would know the answers to all of them without research.

 

Before I forget, I'm not sure that the US uses the MBC any more (and I haven't got into the Howitzer manual yet) but even the MBC had the capability to send and receive data between the FOC and FO. That would certainly reduce the chance of error. One thing I noticed about the MBC is that the list of possible error messages goes on for several pages and most of them are for different types of bad data entry.

[jwduquette1]

Obviously a call for fire isn’t as simple as picking up a radio and sending a message out into the ether and hoping an artillery FDC magically responds. Anybody can theoretically call for fire. It doesn’t mean they are going to get artillery fire.

 

I was often in the loaders position of either the platoon commander or platoon sergeants tank. I was in theory supposed to deal with the radio and understand authentication and all that stuff. As I recall (and it’s been some 20-years, so maybe my mind is failing) but we could input a number of preset frequencies into the radio set -- 10 or maybe it was 20 odd pre-selected frequencies. Changing between frequencies was as simple as pushing the buttons for pre-selected radio stations on your cars stereo. I don’t specifically recall instances of inputting a preset frequency for an Artillery battery FDC -- but than this was the National Guard, and we rarely conducted combined arms training exercises. I would assume that had we been doing more combined arms stuff, than perhaps it would have been fairly routine for the Platoon sergeants and platoon leader’s tanks to have the FDC frequency for a dedicated battery or the battalion’s mortar platoon as pre-selected frequencies. Or is this not correct?

 

As to who's doctrine is better -- UK or US -- I personally could care less. It's a matter of taste or opinion and therefore is not germane to anything being disscussed here.

 

I still think your both out to lunch about the SI angle being of no particular importance for fires involving moderate or large contrasts in altitude (see the threads title again). But I am always willing to listen to reason.

 

The VI is simply the vertical component of the SI angle -- you know TAN(theta) = Y/X and ARCTAN(Y/X) = theta. 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: QE = SI + adj-EL + CE. By the way, the complementary angle of site is calculated directly from the angle of site -- SI. If your ignoring SI as being of no importance to the shoot, you are in essence also saying that CE = 0. CE is a multiple of SI. In other words, you are making "ZERO" elevation correction to your final QE to account for contrast in altitude between battery and target. Sure you can walk the rounds up to the target – assuming that your complete lack of altitude compensation still succeeds in putting spotting rounds within the FOOs line-of-sight, and you haven't just dropped HE onto some of your own guys cause your lack of altitude correction ends up putting the trajectory way short or way over the intended target.

 

I can also see no practical reason for the FO to make his corrections such that fire falls onto the BT line rather than the OT line (unless the two are coincident). This seems rather fundamental to creating a computer program to model FDC calcs. I mean the mechanics are not difficult to work out, the question is why would this be practical and where is this method of adjustment supported in official doctrine – by that I mean where can I find this method of fire and adjust described in FM6-40?

Edited May 14, 2006 by jwduquette1

[jwduquette1]

Having only some class room and simulator experience  with such things, as I recall the FDC 'figures out' degrees or mils by asking the FO for clarification.  Either way the FDC can put one or the other into the computer and get a firing solution and or correction solution.

 

For the US Army, Navy, AF, and USMC, the procedures and terminology are all the same.  They may not be able to talk to each other, but when they can, they all speak the same Indirect Conduct of Fire language.

 

I dare say with all the new fangled GLIDs, GPS, Data Links, et al, much has been forgotten or fallen by the wayside.  The FO of today points his GLID at a target and shoots his laser.  His position, the range to the target, and the azimuth are automatically sent to the FDC and or directly to the guns.

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Understood -- My point was only that we need someone with your level of understanding of tank gunnery mechanics who is an FDC guy. I can waddle through the field manual, but I typically need to work through the finer points with someone that is well versed in the finer points. To that end I think we are sort of spinning our tires here -- creating alot of smoke but going no where. We got one guy talking about mortar gunnery, one guy talking about UK artillery gunnery, and one guy plodding through FM6-40. A sure fire recipe for miscommunication.

Edited May 14, 2006 by jwduquette1

[DKTanker]

Understood -- My point was only that we need someone with your level of understanding of tank gunnery mechanics who is an FDC guy. 

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Maybe ABNredleg will drop by.

[jwduquette1]

Can you give me a link to a site that explains the British system? I have enough questions that it seems unlikely you would know the answers to all of them without research.

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If this is Nigel Evens who's been posting to this thread, he has a great web site located at:

 

http://members.tripod.com/~nigelef/index.htm

 

If this isnt N.E. -- well the above is still a great web site to poke around.

[jwduquette1]

Dunno if this will help or hinder this discussion, but here is a typical set of firing tables for 105mm Howitzer firing HE – charge-2. These are from 1967 and are pretty much public domaine info now. However, if somebody thinks I shouldnt post this stuff lemme know and I'll dump it.

 

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). You can do it one of two ways -- as I perceive it there is the dumbass method that uses the range adjustment thingie (Table B ). Than there is the method for the fellow that’s not an innumerate -- the multiplier in column 12 and 13 of Table G. I like dumbass method as it is elegant, and it saves time as well as wear and tear on the grey matter. Of interest is that old U.S. firing tables circa-WWII and Korea didn’t have the dumbass method. You had to read the multiplier for the complementary angle of site (CAS) for the appropriate range – some fraction per mil of SI – and do the multiplication to come up with a CAS.

 

I have noticed there are no corrections for CAS indicated for Mortars in US Army firing tables – so I assume CAS has no dramatic effect on the much shorter range shoots associated with mortar fire. I haven’t read thru the mortar gunnery FM so I don’t really know wtf is crucial to developing proper firing solutions – and particularly firing solutions based upon moderate to large contrasts in target to shooter altitudes.

 

 

Edited May 15, 2006 by jwduquette1

[jwduquette1]

What did Winston Churchill say? The British and Americans are two peoples separated by a common language? I think that’s what he said – or at least that’s the spirit.

 

To that end this is what I have laying around here on UK indirect fire nomenclature – howitzers and guns -- not mortars. Mind you this is circa 1943. No idea what they call the various bits and pieces now. The point being while the names are different, it is not to difficult to determine what the British are calling something and what the US is calling that the same something.

 

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?

 

The rest of the nomenclature puzzle is relatively self explanatory. Not quite the same names and such used by UK and USA, but certainly the same mechanics are at the heart of the terminology being employed.

 

 

[nigelfe]

Yes, it is me.

 

The problem with the term FDC is that it has had different implications at different times. Classically it was a battalion level entity that combined two functions: deciding what was to be fired (I call this allotment or tactical fire control) and producing the firing data to do it (technical fire control). However, since Vietnam time (or the adoption of BCS) I understand that most if not all US arty has actually done technical fire control in each gun battery leaving tac FC with a bn FDC, this is the role I was referring to. UK has always done their tech FC at battery level.

 

If you are using predicted fire then the most accurate possible calculations are needed. However, if its adjusted then, particularly with manual calculations, there's some tradeoff between time and accuracy if you want and your regs allow. Obviously with computers they do the full calcs every time.

 

Computers don't automate the manual calcs, although some 1970/80s backup devices using hand held calculators were fairly close and used polynomials derived from FT type data not the aeroballistic data used by computers. Starting wayback with FADAC, computers simulate the trajectory, they 'guess' a bearing, elevation and charge then calculate the trajectory in small time of flight steps, when they reach the target height they compare the impact location with the tgt location and then adjust their starting conditions and try again. They stop iterating when the impact location is within the tolerance distance of the tgt loc (and yes I know MLRS was/is different).

 

Obviously FADAC took a few simplifying short cuts (eg I don't think it calculated the traj for each individual gun in a bty, it did one and extrapolated from it for MV and position differences of the others) and used the point mass model (3 Degrees of Freedom) of a shell. BCS used the modified point mass model (4 DF) and calculated for each gun individually. Later systems use the most accurate possible approach but generally similar to BCS and now everyone (in NATO) is changing to the NABK model as they introduce new systems.

 

Getting back to manual calcs and diff alt, which I think was the question. The traditional method was the increase the elevation angle (QE) by adding the angle of sight (gun to target) to Tangent Elev. However, this creates a hypoteneuse to the horizontal plane at the gun and this hypoteneuse is a different length to the horizontal distance. Therefore a correction is needed, which reflects the angle of descent, this is called 'non-rigidity of the trajectory' and is provided in FTs. There's a picture on the 'Basics of Gunnery' page on my web site. Computers don't need it because of the way they calculate firing data.

[jwduquette1]

In WW2 the Brits didn't usually bother about angle of sight for observed fire unless it was very large.

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Determination of sight angle in long range direct fire was in reference to a disscussion regarding a first round hit on a tank at 5100m using HEP. It's doubtful that you can ignore any potential source of error in the initial launch angle and still claim that a first round hit at that sort of range was anything other than an extreme bit of luck. But this was an aside, and nothing to do with my original question.

 

The question was that determination of SI is straight forward in long range direct fire, but not in indirect fire. The FO is directing fire to a location where he thinks the target is. If he is off 300 or 400meters in the horizontal plane for his target location estimate, the contrast in target altitude from the assumed target position and the actual target position could potentially be considerable. So if the FDC is setting his target pin on a map grid location and determing altitude at the presumed target location and subsequently determining SI and CAS based upon the assumed target altitude, the error in the shoot could also be quite considerable. An FO correction (assuming he can see the burst when the firing solution includes a gross error in SI and CAS) based upon the initially bad SI + CAS setting could also be of little real value unless the SI and CAS are also adjusted.

Edited May 17, 2006 by jwduquette1

[nigelfe]

I normally only deal with indirect fire.

 

Direct fire is short range (ie a few km) and mostly a fairly flat trajectory. It's also usually against vertical targets. Since the firing tank (or Atk gun) is measuring the range (ie the hypoteneuse) then I'd say that obviously angle of sight isn't an issue. Furthermore I don't think non-rigidity of the traj is an issue either. The exception would be a low velocity shell at a fairly large a of s when NR could be a factor. Of course if you are worrying about mm in the vertical plan then NR could be an issue under most conditions although it would be hidden by normal rd to rd variability.

 

In normal procedures (LRF and Danger Close are different) the somewhat mechanistic process of adjustment is very simple. First the FO brings the fall of shot onto the line OT (or GT, or an arbitrary bg - either being generally used if the observer is moving around, eg in a heli). Having got a shell falling on or close to OT line (close enough to the line to what he's picked as his adjusting point, close enough meaning he can be totally sure whether a rd falls over or short) he then starts a binary search routine of bracketing the target. Somewhere in this process he will eventually get a bracket of 100m or 50m (not necessarily from consecutive rds), which he can split and order FFE sure in the knowledge that the mpi of the FFE will be in effective distance of the point he selected as representing tgt centre. For bracketing the slope of the ground doesn't matter, his goal is to achieve a short bracket. The initial line correction can be a bit trickier depending on the relationship between the slope of the ground and the line of fire, not forgetting the added complication of a larger angle T. Where the slope, etc, is a bit difficult he may need more than a single rd to get onto OT, and in extremis (shock, horror) he can bracket for the line correction but really only inexperienced observers who get into difficulties.

 

There is an element of FO skill and experience in this, that's why claiming that any inexperienced soldier can do it is a load of optimistic phooey, in ideal conditions yes, but conditions are seldom that way. It's quicker if an inexperienced observer reports his observations to an experienced observer who can then judge the corrections needed. The point about the adjustment process is that the guy watching the fall of shot is the guy who can actually see what's happening and is best placed to judge the call or tell someone competant exactly what he sees.

[jwduquette1]

Thanks for your efforts, but never mind. I can see I'm making no headway in getting you to see what I am talking about. Things are being repeated that I or others have already said earlier in the thread -- ala non-rigidity and direct fire of high velocity weapons. This is always a bad sign for longevity of a discussion. Besides, I found the answer to my question under replot procedures detailed in FM6-40.

 

Best Regards

JD

[nigelfe]

Some time ago, in another thread on another forum, I was surprised to hear someone who said they had experience as an artillery FO say that it is not possible to adjust fire unless you are on the Gun-Target line.

 

 

The question is: does it make sense to take the relative elevation of the target into consideration when figuring firing corrections based on observer input? I'm having difficulty visualizing the trigonometry involved.

 

Any suggestions . . . other than "Give it up"? 

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The answer to the first point is 'yes you can' (but it needs a bit of skill).

 

To the second 'no' (because the process of adjustment 'shoots out' the problem). However, if you are using LRF and polar coords the answer is 'yes' because you're trying for a single correction to hit the target.

 

I haven't a clue what 6-40 states but if it says otherwise then it's lost the plot, alternatively it may be talking about a different subject, what used to be called ARFAS (adjustment of range for false angle of sight) which takes as-fired gun data and deduces tgt coords, the problem being to find the right split of QE between TE and AoS.

[starkweatherr]

I understand what you are both saying. Thanks for the info on the British system, Nigel. We are kind of talking about apples and oranges, though.

 

JW, I'm going to have to draw myself a picture before I can figure out what I think I want to say. I guess that's why I asked in the scientific forum. I have the feeling that the SI angle is less important for direct fire because, at some point you have some part of the sight reticle on the target, which should allow the ballistic computer to make some adjustment for the elevation difference.

 

I think that during the Korean Conflict, when we used ramp mounted tanks as artillery, they were controlled as artillery, too. If making a really long HEP shot, I would hope that I could put some part of the sight on the target and, knowing the approximate range, make minor adjustments that didn't involve calculations or firing tables. We did this in Germany with a long range HEP target, and most tanks got close enough with the first round to score, or else didn't hit anywhere near it for some reason, like having the wrong type of ammunition indexed in the ballistic computer.

[nigelfe]

Tanks were used in fireplans in WW2. Post war they retained an indirect fire role, meaing thy didn't see the target. UK Centurians were equipped with a plotter for indirect fire (form not known). I've never enquired how they oriented or what they did about an aiming point. Using the traverse indicator would be one way, but it wasn't very finely graduated.

[jwduquette1]

I understand what you are both saying. Thanks for the info on the British system, Nigel. We are kind of talking about apples and oranges, though.

 

JW, I'm going to have to draw myself a picture before I can figure out what I think I want to say. I guess that's why I asked in the scientific forum. I have the feeling that the SI angle is less important for direct fire because, at some point you have some part of the sight reticle on the target, which should allow the ballistic computer to make some adjustment for the elevation difference.

 

I think that during the Korean Conflict, when we used ramp mounted tanks as artillery, they were controlled as artillery, too. If making a really long HEP shot, I would hope that I could put some part of the sight on the target and, knowing the approximate range, make minor adjustments that didn't involve calculations or firing tables. We did this in Germany with a long range HEP target, and most tanks got close enough with the first round to score, or else didn't hit anywhere near it for some reason, like having the wrong type of ammunition indexed in the ballistic computer.

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SI angle is of little importance to direct fire -- unless there is a large contrast in altitude between target and shooter – particularly if we are talking about longer range direct fire – ala a 5100m HEP shot. Regarding the ballistic computer on say earlier versions of the M60s or M48A5s, how is it accounting for large contrasts in altitude between target and shooter? Are you saying this was somehow done automatically by the computer? How would the ballistic computer know if the range input by the TC represents a target 500m above you or at the same level as you? In other words the computer somehow automatically inputs a superelevation that accounts for altitude contrasts? I dont think this is true -- but if it is I would be interested in someone explaining the mechanics in how the computer does this.

[DKTanker]

SI angle is of little importance to direct fire -- unless there is a large contrast in altitude between target and shooter – particularly if we are talking about longer range direct fire – ala a 5100m HEP shot.  Regarding the ballistic computer on say earlier versions of the M60s or M48A5s, how is it accounting for large contrasts in altitude between target and shooter?  Are you saying this was somehow done automatically by the computer?  How would the ballistic computer know if the range input by the TC represents a target 500m above you or at the same level as you?  In other words the computer somehow automatically inputs a superelevation that accounts for altitude contrasts?  I dont think this is true -- but if it is I would be interested in someone explaining the mechanics in how the computer does this.

323917[/snapback]

Neither the M13 computer of the M48A5/M60A1s, M22 of the M60A3, nor the computer on the M1/M1A1 (I don't have the first clue about the M1A2 and sub variants) resolve for a change in elevation between the firing tank and target.

 

I don't know why the M60A3 through M1A1 didn't calculate the change in elevation. It would have been a very simple calculation on par with calculating cant solutions and very useful even at fairly close ranges* (less than 2000 meters).

 

*Range 117 Graf. When the firing tank was at the end of the course road there was a target on the right side of the range that was at a higher elevation than was the firing tank. Everyone that I know who hit this target first round did so by aiming top half of the target (It was usually a TC engagement). Also at Wildflecken, when firing across the valley, most gunners learned to aim base of target because the targets were significantly lower in elevation.

[jwduquette1]

Neither the M13 computer of the M48A5/M60A1s, M22 of the M60A3, nor the computer on the M1/M1A1 (I don't have the first clue about the M1A2 and sub variants) resolve for a change in elevation between the firing tank and target.

 

I don't know why the M60A3 through M1A1 didn't calculate the change in elevation.  It would have been a very simple calculation on par with calculating cant solutions and very useful even at fairly close ranges* (less than 2000 meters).

 

*Range 117 Graf.  When the firing tank was at the end of the course road there was a target on the right side of the range that was at a higher elevation than was the firing tank.  Everyone that I know who hit this target first round did so by aiming top half of the target (It was usually a TC engagement).  Also at Wildflecken, when firing across the valley, most gunners learned to aim base of target because the targets were significantly lower in elevation.

323947[/snapback]

 

Thanks Dave. Aside from the one day of main gun shooting at Ft. Knox during advanced individual training, I did all my gunnery training at Ft Irwin. As I recall these were pretty much bowling ball flat ranges and we were not shooting main gun engagements beyond about 1500m or 2000m. We didn’t have lasers or the like back than – at least not in my Guard unit. Range was still being determined by the TC using the optical range finder.

 

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?

 

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?

 

Regards

JD