Artillery Systems Characterisation
Artillery System Characterisation.
The US artillery community believes that to engage a target accurately, regardless of range there are certain sets of data required.
Below is a section from FM 6-40, Tactics, Techniques & Procedures for Field Artillery Manual Cannon Gunnery:
“
1-3. Five Requirements for Accurate Predicted Fire
To achieve accurate first-round fire for effect (FFE) on a target, an artillery unit must compensate for nonstandard conditions as completely as time and the tactical situation permit. There are five requirements for achieving accurate first-round fire for effect.
These requirements are:
1. Accurate target location and size
2. Firing unit location
3. Weapon and ammunition information
4. Meteorological information
5. Computational procedures.
If these requirements are met, the firing unit will be able to deliver accurate and timely fires in support of the ground-gaining arms.”
As we can see from this the actual weapon system is only half of one of these critical features, the other being the ammunition. Both projectiles and charges.
Weapon Aspects
With regards to the weapon the critical aspects are the accuracy of its Fire Control, how well the Fire Control had been aligned (Boresighted) to the tube, and any slop/backlash within the elevation and traversing mechanisms of the weapon. Any modern fire control system, be it glass and iron or a digital system using an INU should be able to maintain an alignment of within 0.5 mils in both elevation and azimuth through the full range of elevation and traverse.
The Mil is the standard term used for angular measurement within the artillery community. In western militaries there are 6400 mils in one revolution. In the Former Warsaw Pact there is either 6000 or 6200 (Maybe someone can confirm for me?). Needless to say it is a rather small angle!!! (0.056 Degrees). The western system is very convenient as it is almost exactly the angle formed by a 1 meter opposite side of a triangle with adjacent side 1000 meters.
Ammunition Aspects.
With regards to the Ammunition the critical aspects are consistency of weight, dimensions, Centre of Gravity and Surface finish for the Projectile, and for the charge it is consistency of developed chamber pressure and hence developed muzzle velocity. These all impact the ballistic performance of the round as it travels through the air with regards to consistency and conformance to the theoretical model.
What does all this mean to the 0.38% Probable Error in Range, and the 0.58 Mils Deflection errors quoted for the G6 Howitzer, V-LAP Projectile and Zone 6 charge combination I quoted in my original post?
Well, if the test was carried out like those I have been involved with in the US these numbers are not a measure of the systems accuracy, but of its precision. These are two very different and often confused terms.
Because a systems accuracy is affected and in fact dominated by aspects other than the weapon these variable must be eliminated. This is done as follows:
1. Target Location.
For weapon characterization there is no actual target, rather the impacts are very precisely spotted by using a minimum of 4 observers arrayed parallel to the line of fire. Each observer is set op on a known surveyed position, accurate to within 1 meter, usually less. Each one of them will determine an azimuth to the impact and the centre of the smallest triangle formed by any three of these observers azimuths is recorded as the impact point.
2. Firing Unit Location
Even though the weapon systems may have an onboard Nav system, once again the actual position of the weapon is precisely surveyed in to an accuracy of less than 1 meter.
3. Weapon and Ammunition
The weapons Fire Control is verified as being aligned and the charges and projectiles are conditioned, usually at 70 Degrees F.
4. Meteorological Data.
Met is collected at the optimum point of the trajectory and up dated as often as possible.
5. Computation
As explained weapon characterization is not a test of the validity and accuracy of the computational model, this is just used initially to determine a solution to hit within a desired impact zone where the observers can get good observations on the impacts. All shots will be fired on the same Azimuth and Elevation unless a huge change in Met conditions would put the impacts out of the safety zone.
The weapon will fire groups of rounds within a certain time frame, usually 10 - 15 rounds within a 30 minute period. This constitutes on group. For this group of impacts the Mean Point of Impact is calculated and the spread of the rounds from this point in range and deflection are what is used to generate thenumbers initially quoted.
To get statistical validity several hundred if not thousands of groups must be fired. Only then can reliable values for Range Probable Error and Deflection Error be obtained.
Assuming this was how the G6 76km shots were assessed we can tell the following:
The 0.38% Probable Error in Range means that 50% of the rounds fired landed no further than +/- 0.0038 x 76000 = 288 meters from teh MPI along the Azimuth to Mean Point of Impact Line.
Doesnt quite seem so impressive now does it? But trust me at that range actually it is
With regards to Deflection ie the spread left to right of the Azimuth to MPI line, or "Mean Deflection Line", because this property has not been quoted as a Probable Error but as an actual angular measurement we can infer that 100% of the rounds lie within this. At 76,000 meters this 0.58 mils equates to within 43 meters left and right of the MPI. This is actually VERY impressive at that range.
This is exactly what I would expect to see, range errors are always considerably greater than deflection errors.
Hope this little ramble hasnt bored anyone to tears. If you want I can explain the joys of Realistic Accuracy Testing , Hasty Survey, poorly conditioned charges, Stale Met poorly positioned Forward Observer and so on, not to mention the fun of calculating Circular Error Probable. then arguing over the results and whether it was a "Fair Test" or not.
Regarding the question of the zone 6 charge used, here is an image of the Current US Modular Charge System and its equivilent Bag Charges.
http://i50.photobucket.com/albums/f332/adjstewart/Military/macsbag2.gif
Note the Zone 6 charge whch was being developed for crusader but is no defunct has no equivilent bag charge. This is the same for all current zone 6 charges, be they South African, Japanese or whoever.
