Why was Artillery used in the Direct Fire role in Kargil?
Good question.
Arty is an AREA weapon. In other words, it covers and area and does not have a pin point MPI. as would a rifle have.
Let me explain arty fire from some material that I have of WW II. Note: because it is WWII it does not mean that the behaviour of shells has changed.
Accuracy and Consistency
Errors are in one of two categories - accuracy or consistency. Accuracy means the closeness of the mean outcome to where it should be. For example the difference between the mean point of impact (MPI) of fall of shot and their aim point. Consistency means the size of the spread of outcomes (eg shells) around their MPI. In artillery this variability is called 'consistency' or 'dispersion' (the optimistic or pessimistic views of the world - do you call a glass half-full or half-empty?), elsewhere it is sometimes called 'precision'. Nevertheless in practical terms sources of inaccuracy may include mistakes as well as errors and in some cases the division is a fine one and routine human mistakes may be treated as errors.
For artillery fire there are two main components to accuracy, how close the aimpoint is to the actual target (sometimes called the 'target location error') and then how close the fire unit's shells' MPI is to their aimpoint. The first is a function of the accuracy and consistency of the target acquisition system and how accurate the target coordinates are, not just horizontally but also altitude because an error in altitude causes a horizontal error in fall of shot. The accuracy and consistency of the second is mostly a function of the data and methods used to 'fix' and orient (ie survey) the guns and to calculate their firing data. The purpose of ranging is to correct for these sources of inaccuracy. However, inaccuracy also arose from day to day variations from the calibrated muzzle velocity.
Figure 1 illustrates the concept in terms of the fall of shot around an aimpoint. Of course the apparent irregularity really reflects the small size of the sample.
The main driver of consistency is the extent of the round to round variation in muzzle velocity (MV), and this is mostly a function of the ammunition, both shell and propellant, and its design, manufacture and handling. The tightness of quality control in keeping it to its specifications (eg propellant energy, shell weight and shape) is a major factor. Other sources of variation are due to differences in ammunition storage and handling at the gun and how strongly the shell is rammed. Unpacked ammunition that has been sitting in the sun will perform slightly differently to that taken directly from its packaging. Nevertheless there are differences in the probable errors in the range or firing tables for different guns firing the same ammunition, look at the two 7.2 inch in Figure 4 below, and consider the different carriage stability characteristics in the gun data sheet. Of course in some cases this may reflect differences in national measuring and calculating methods. Consistency also deteriorates when a gun is well worn because barrel wear makes the shell less stable in flight.
Round to round variations also occur due to very small inconsistencies in laying causing the gun to be pointed in fractionally different directions for each round. To this can be added very small variations due to the continuously changing atmospheric conditions that affect the shells' flight, and shells at transonic speed are notably less consistent than those above or below this speed. There are also small variations in gun specific characteristics such as jump and droop. Finally there are residual factors that are not properly understood, see Calibration.
The main sources of lack of accuracy are mostly not an inherent characteristic of a gun, Table 1 and 2 later on this page show this. Only two of any size might the considered gun dependent, and they are dwarfed by others. The first of these is the graduation of sights, and this is basically the same for all guns, the basic unit of measurement, 5 minutes in UK, had specific distance on the ground depending on range, charge and the type of gun. There are also day to day variations and although these are about their mean, they can cause inaccuracy on an occasion to occasion basis. The most significant is again muzzle velocity, and trials demonstrated a day to day correlation between guns in a troop, ie the group of guns tended to be effected the same way each day. Apart from these it is really a matter of the quality of data in range tables, the quality of data about current non-standard conditions (meteor and propellant temperature, plus muzzle velocity) and the accuracy of the methods used to combine these to produce firing data. Not forgetting the entirely external sources of survey accuracy and target location error.
Of course to an observer there may be a perception of gun accuracy but this is probably a mixture of consistency and occasion to occasion error. Assuming an accurately located target and predicted fire then a single round from a consistent gun will usually appear more accurate than one from a less consistent gun because it will probably be closer to the target. However, the mean of several shells could be correct in both cases.
Probability
Both accuracy and consistency are measured in terms of 'Probable Errors' (PE) and exist throughout the artillery system. For example the MPI of the fall of shot from a single gun may or may not be at its aimpoint. The distance MPI to aimpoint is accuracy, the size of the fall of shot's spread around its MPI is its consistency. Similarly the MPI of the MPIs of each gun in a battery will be the battery MPI, and the MPI of the MPIs of the batteries in a regiment will give a regimental MPI (assuming they were all aimed at the same point). The measure of how far these MPIs are from their common aimpoint is their accuracy and is also defined in terms of PEs.
Conventional statistics defines variability in terms of 'standard deviations' from the mean with a 'normal distribution' (a 'bell curve'), such that all outcomes for a particular type of event will fall within about three standard deviations from the mean of them. Artillery does not use standard deviations, but 'probable errors' (PEs). In essence its just a matter of slicing up the spread of outcomes in a different way. Instead of them all falling within 6 standard deviations of the mean (3 either side) they fall within 8 PEs, 4 either side of the mean, the total distance is the same. Figure 2 shows the normal proportional distribution of outcomes for an event. The 2 PEs (one either side of the MPI) are called the 50% zone, because 50% of the shells fall there, the central 4 PEs give the 82% zone, and so on. The size of a PE will vary but their distribution does not, Figure 2 shows the distribution of PEs as a histogram, the horizontal axis represents the size of a PE. A small number, about 1 per 500, fall outside the 100% zone.
PEs occur throughout the artillery system. For example the spread of the fall of shot from an individual gun firing repeated shells at the same data, the size of these PEs are documented in Range Tables. For a 25-pdr firing charge 3 at 8000 yds range the PER was 30 yds (PE range - along the line of fire) and PEL was 4 yds (PE line - across the line of fire). Figure 3 illustrates the distribution of 100 shells when combining their range and line PE, (rounded numbers). Of course it's also possible, but unlikely, for a shell to fall at the extreme of both range and line PEs. Most properly conducted actions in the artillery system (eg plotting on an artillery board, the target location, laying) have a normal distribution of errors, some of them circular.
For fall of shot from an individual gun It must, of course be remembered that the PEL is much smaller than the PER, this means that in distance terms 50% of the rounds will fall within one PER of the target.
Figure 4 shows British WW2 guns and their dispersion PER as a percentage of range. For comparison a WW1 gun (6-inch Gun Mk 19) and 1960's design (155-mm L121 (FH70)) are also shown. The PEs, taken from Range Tables, are for the charge with the smallest at each range. However, British WW2 Range Tables only gave PER to the nearest 5 yards, which probably explains the slightly erratic data.
For some variables the PE could be circular around the mean (PEC), with 1 PEC (or CEP) all round being the 50% zone. PE for different things can be added together using the 'root mean square' rule (square the PEs, add them together and find the square root). This reflects the reality that errors on the same axis partially cancel each other out.
However, this is only valid if all the errors are in the same dimension. The disparity in the size of PEL and PER, which are in different dimensions (axes), means that combining them to give a CEP is misleading because the two axes give an eliptical not circular shape (Figure 3 above). Where two dimensions are equal size then the CEP is 1.75 × PE. Where they are reaonably close, say PER25m and PEL20m, then the square root of the average of their squares is a reasonable appoximation, 32m CEP in this case. However, when they are far apart, eg PER25m and PEL5m, this method gives 18m CEP (or 21 yards CEP in the 25-pdr example above), a useful 'improvement' in PER but clearly an impossibility. Nevertheless, CEPs do appear in manufacturers' brochures and are quoted, and sometimes manufacturers add another layer of obfuscation by presenting this CEP as a percentage of range!
In the mountains, apart from the issues mentioned above, there is also the rarefied atmosphere as also the weather changes rapidly.
Therefore, as is routine, Datum shoots are fired to check accuracy in the changed conditions. It is normal done every 2 hours.
Mountain peaks being small where the enemy is entrenched, apart from the above issues, the area on which the shots are to fall are very small.
Therefore, quite a few shells fall "Over'" i.e. go beyond that small pinnacle or fall "Under" ie. fall short of the small target area.
Hence, a large number of shells or rounds have to be fired for the desired effect on the target.
Now, if the enemy post can be seen, it is easier to use the Arty gun like a rifle, if you will, so that the Overs and Unders are eliminated and accuracy and effect becomes better.
Hence, the Direct Firing was resorted to by Lucky Lakhinder.
