the field artillery journal - Fort Sill - U.S. Army

Figure 8
90º as the case may be, the desired direction is determined (see
Fig. 8).
Although the most accurate, the third method is more
complicated and takes longer than the first two. With this
method three distinct operations must be performed: (1) the
point of detonation must be determined, (2) the fuze and fin
hole must be located, and (3) the direction of the line formed by
(1) and (2) must be measured. The point of detonation is the
point in the ground at which the explosion occurs. It is also the
focal point for shell splinters. Hence, back tracking along the
splinter grooves will provide a point of intersection, which point
is the point of detonation. A practical method for determining
this point is to line in a small stake with the aforementioned
grooves. When so aligned, the stake will be directly above the
desired point. See Fig. 9. The fuze and fin hole are located
under the loose earth covering the bottom of the crater. In soft
ground
the fins and fuze particles normally will bury themselves
at a considerable depth along the line of the trajectory. The hole
formed by these particles is the fuze and fin hole. To locate the
actual hole, remove the loose earth until the fins are uncovered.
In soft ground they may be at the bottom of a small tunnel, in
which case care should be taken not to damage the firm sides of
Figure 9
the tunnel, as this gives a clue to direction. Upon removal of the
fins, the fuze splinters will be found. The third operation in
determining the direction from which the mortar was fired is to
measure the azimuth between the center of the fuze and fin hole
and the point of detonation. This also may be accomplished by
laying a stick between the two and measuring its azimuth with a
prismatic or other type compass.
The value of each method outlined in the preceding
paragraphs depends upon the type of ground on which the shell
explodes, but it will usually be found that direction is best
found by a combination of all methods regardless of the type
soil encountered. When a number of craters can be examined
the mean direction should be taken for as many as possible in
the time available.
In the above method for determining direction no allowance
has been made for the effect of wind upon the projectile. The
direction determined, therefore, is that of the line of flight of
the projectile at the end of its travel. A more accurate line from
crater to mortar will be found if allowance is made for cross
wind. For a light cross wind correct the azimuth from the crater
with the wind by 4º, and for a strong cross wind 8º (see Fig. 10).
Figure 10
Range Determination
Angle of fall, which approximates the elevation at which the
mortar was fired, can also be determined by analysis of the
shell crater. This angle, when included in the Shellrep, with the
caliber of the mortar can be of value in determining the range
at which the mortar was fired. Equipment not usually carried
by the individual, however, is necessary—a protractor and a
plumb bob (see Fig. 11).
The angle of fall can be found most accurately when the
ground is soft and the fins and fuze fragments bury deeply.
Find the point of detonation as for finding direction and drive
Figure 11