spotting and deflection correction in roils, to be placed
estimates the distance to the reference point. Then he
determines the correction in meters from the reference
on the mortar sight, are the same. The tactical
point to the OT line by use of the mil-relation formula
employment of the mortar usually makes it necessary
or the deflection table and the observer reference-point
for the forward observer to be in a position other than at
distance. He includes this deviation correction in his call
the mortar; however, when the forward observer is
for fire.
located within 100 meters of the mortar position, the
deviation error that he reads in his binoculars can be
2. HEIGHT OF TARGET. When the difference in
applied directly to the sight without any computations.
altitude between the reference point and the target is 50
This is true because the angle that exists between the
or greater, this connection is announced in the call for
observer-burst line and observer-target line is, for all
fire. The height of the target may be determined as
practical purposes, equal to the angle that exists between
follows: Measure the angle of site to the target and to
the mortar-burst and the gun-target lines. Any slight
the reference point; then, by the mil relation, compute
difference between these two angles is compensated for
the amount so each is above or below the observation
by the inherent dispersion of the weapon and the
point. From these values, compute the connection for
-
bursting area of the round. For example, when the
difference in altitude of reference point and target.
observer, from a position within 100 meters of the
3. RANGE. The forward observer estimates the
mortar location, observes the burst to the left of the
distance along the OT line to the target from the
target and reads that it is 40 mils left on the mil scale of
reference point. This distance is the range correction and
his binoculars, he orders a correction of
is included in his call for fire.
RIGHT-FOUR-ZERO.
The shift method gives accurate results for shifts of
The gunner applies this connection directly to the
400 mils or less and acceptable results for shifts up to
previous deflection setting, using the LARS (left add,
600 mils. For greater shifts in direction, the deviation
right subtract) rule.
error and the difficulty of estimating the distance from
the reference to the target increase rapidly. For this
Observer More than 100 Meters from the Mortar
reason, the forward observer selects and adjusts on other
Position. It is not always possible for the observer to be
reference points so the large shifts to any likely targets
located within 100 meters of the mortar position. When
can be kept to a minimum.
he cannot locate himself within 100 meters of the
mortar position, he must locate himself within 100
POLAR COORDINATES. When the forward
meters of the gun-target line. It can be readily seen
observer's location is known by the FDC, report the
that this might present some difficulty in
initial location of the target by polar coordinates. The
visualizing the gun-target line and getting within
FDC plots the target along the azimuth and at the range
100 meters of it. When the observer is attacking
from the observer's location as reported by the observer.
targets over a wide frontage, he is required to move
This method is particularly desirable in the case of large
frequently and his movement is limited. In this
lateral shifts and short observing (OT) distances. When
situation, the angle that exists between the
the observer's location is not known at the FDC, he may
mortar-burst and the gun-target line is not equal to
send it by grid coordinates or some other means.
the angle that exists between the observer-burst and
the observer-target line, and certain computations
Correction by the Forward Observer
must be made to correct the differences in these
angles. For example, when the observer is halfway
between the mortar and the target, the correction to
In fire without an FDC, the forward observer makes
be made on the sight is one half of his deviation
corrections differently than when operating with a fire
spotting; when the mortar is halfway between the
direction center. He makes all deviation connections with
observer and the target, the correction is twice his
respect to the gun-target line rather than with respect to
deviation spotting. As other distances give other
the observer-target line. All deviation corrections are
ratios, it is necessary to apply a correction factor to
sent to the mortar in mils or turns of the traversing
the number of mils spotted before ordering a
handwheel.
deflection change. This factor is a fraction, the
numerator of which is the observer-target distance,
Observer Within 100 Meters of the Mortar Position.
The best location for the forward observer for rapid-fire
and the denominator of which is the gun-target
adjustment is at the mortar position where his deviation
distance; that is
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