Sighting methods
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In order that a shell
from a gun hit the target, the gun should fire at a certain angle of
elevation depending on the range, the ballistic characteristics of the gun,
and upon the relative level of the gun and target. It should be given such a
direction to the right or left of the target as to offset the deviation of the
projectile due to drift and wind. The sights of the gun provided means of
determining when the axis of the gun had the predetermined direction. The simplest sight was the one over the line of metal,
which laid for direction only. The second was the tangent sight, mounted on a
range arc centred on the axis of rotation in elevation, usually having a
deflection scale to correct for drift and to lead a moving target. It laid
for range and direction. The telescopic or panoramic sight was mounted on a
range arc and laid for direction only, the unit in direct fire laying for
range and direction and markedly improving the vision of the gunner. Direct
laying When the piece was
sighted, both in elevation and direction by sighting directly on the target,
the method was known as direct laying. The line of sight was
fixed in two different ways. The first method was to use plain or open
sights, the rear one of which had a peep, or notch, capable of adjustment in
a vertical or horizontal direction. This rear sight was equipped with an arc
reading in fractions of the range, or degrees, by which the necessary
elevation could be set off. In some cases the rear sight was designed to
automatically correct for drift; if not, the drift had to be set off on a
scale provided for this purpose on the rear sight. The projectile followed
the movement of the rear sight, going higher as the sight was raised, and to
the right or left as the sight was moved to the right or left. The second method for
direct laying was to use a telescope with cross hairs which took the place of
the open sights although its principle of operation was the same. The angle of elevation
of a gun must be measured in the vertical plane through the axis of the
piece. Since frequently happened that a mobile piece should be fired under
conditions in which the trunnion axis was not level, thereby throwing the
sight plane out of the vertical, the sight arm should be revolved about an
axis parallel to the axis of the gun until the sight arm was vertical. At the
beginning of World War 1 most wheeled carriage
had such a provision made on their sights. Indirect
laying The gun was said to be
laid indirectly when it was laid by means other than aiming directly through
the sights at the targets. The fire from modern quick-firing field guns was
so accurate and destructive that it was always necessary to establish field
batteries in position out of the view of the enemy for the sake of
protection. Consequently indirect sighting became the usual method of
sighting guns. The line of sight was
fixed in four different ways: - by an auxiliary mark, called aiming point, for line,
and by clinometer for elevation; - by direct vision for line, and by clinometer for
elevation; - by an aiming point both for line and for elevation; - by aiming point for line, and by direct vision for
elevation. In French
artillery indirect laying was normally used, even if the targed was visible
from the guns. During the war against The Turks, trained in the German school
and lacking in the latest mechanical improvements in equipment, seemed either
to have been ignorant of indirect fire, or else to have deliberately ignored
it. Rarely did they place their guns in masked positions for indirect fire,
although often positions affording flash defilade could easily have been
obtained. Sometimes, however, three guns of a battery were concealed, the
other, used as a directing piece, being left in the open or placed so as to
fire directly over the crest. This almost always led to its destruction,
although the other guns, at some distance to the right or left escaped. The panorama sight The panoramic sight
afforded the means of aiming the gun in indirect laying by directing the line
of sight on any object in view from the gun; at the same time it afforded the
advantage of a telescopic sight in direct or indirect aiming. At the
beginning of World War 1 the Goerz
panorama sight was almost universally adopted. This panoramic sight
was a telescope so fitted with a rotating head, reflectors and prisms, that a
magnified image of an object anywhere in view could be brought to the eye without
change in the position of the observer’s eye. The panoramic sight was
often mounted in connection with the range-sighting mechanism, but sometimes
in order to divide the duties of laying for direction and elevation, the
panoramic sight was mounted on a shank on the left side of the cradle and
used in laying for direction, while the range quadrant for laying in
elevation was placed on the right side of the cradle
and used by another gunner. In connection with the
range quadrant a range level was provided, which was a special form of
clinometer. It was used in setting off the angle of site, thereby correcting
for difference in level of the gun or target. The range quadrant was
graduated in degrees or in fractions of the range. In the case of howitzers,
the different zones of fire were sometimes shown. While the use of the range quadrant separated the
duties of the gunners in aiming, it did not comply with the conditions for
the independent line of sight. The sight and
range quadrant being attached to the cradle, both moved in elevation with the
gun. The independent line of sight permitted to move and set in elevation a
gun without any change in position of the sight used for direction aiming. |
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Use of the aiming circle |
