Elvis
Posts: 86
Joined: 6/20/2000
From: Clarion, PA
Status: offline
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Also, some info from the same sources on the issue of dispersion.
Shells from a single gun will tend to deviate over a rectangular or elliptical area whose longer axis is along the line between the gun and target (The Gun-Target Line).
Disregarding complete misses, you can place a rectangle over the area the shots are landing. If you divide that area into four parts in each direction along the long axis, it will be found that roughly half the shells in that direction will land within the first quarter. If you take the remaining 3/4, roughly half the remainder will fall in the first quarter of that range, etc. The same effect happens in the other dimension, though the divisions are smaller since there is less dispersion in that direction.
Putting it all together, you get, in percentages that a shell will hit each sector:
[code]0.04 0.14 0.32 0.50 0.50 0.32 0.14 0.04
0.14 0.49 1.12 1.75 1.75 1.12 0.49 0.14
0.32 1.12 2.56 4.00 4.00 2.56 1.12 0.32
0.50 1.75 4.00 6.25 6.25 4.00 1.75 0.50
0.50 1.75 4.00 6.25 6.25 4.00 1.75 0.50
0.32 1.12 2.56 4.00 4.00 2.56 1.12 0.32
0.14 0.49 1.12 1.75 1.75 1.12 0.49 0.14
0.04 0.14 0.32 0.50 0.50 0.32 0.14 0.04[/code]
Another way to look at this is as an expanding series of rectangular zones. 25% of the shells will land in the central four rectangles (the 2x2 area of "6.25's"); 68% in the first plus the next ring out (the 4x4 area in the center); 91% in the next ring out (6x6); and of course 100% in the whole 8x8 area.
The dimension of this rectangle is much longer in the direction of fire than in the lateral direction -- typically by a factor of 4-5. Each 1/8 division along the long axis (the line of fire) is known as a range probable error; along the short axis is a deflection probable error.
For the 155mm gun M1 at 18000 yards, the range probable error is 43 meters and the deflection probable error is 9 meters, so the whole rectangle is 344x72 meters.
By using the range probable errors, you can compute the chance that a shell will directly hit a target of a particular size if the guns are aimed perfectly.
For instance, in the above example a 86x18 meter target with its long axis aligned with the line of fire would be hit by 25% of the shells impacting in the target area, since it's the same size as the central 25% rectangle.
An AT gun, taking up 4.3x0.9 meters, being 1/400th of that size, would be hit by about .0625% of the shells hitting the target area, so you'd have to fire about 1600 rounds at it for a direct hit.
(Although taking burst radius into effect makes it entirely possible to destroy the weapon without a direct hit.)
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Artillery Effectiveness (yet again) - 
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