Handbook for Light Artillery

by A. B. Dyer

Under certain circumstances it is advisable to ascertain the range of points in the line of march of the target. When the moving target reaches one of these points, fire rapidly. Infantry cover 1½ yards a second at a quick walk, and artillery and cavalry 2 yards a second at a quick walk, 4 yards at a trot, and 6 yards at a gallop. By multiplying the rate per second of the target by the time of flight of a shell, we obtain the distance the target has moved over during the flight of the shell.

INDIRECT FIRING.

In firing at an object which cannot be seen from the gun several methods are employed, depending on the circumstances of the case.

1st. Plant a picket for each gun on the crest of the ridge whence the object to be fired at can be seen; behind the ridge line a second picket with the first picket and the object, run the guns up to any convenient distance in rear of the pickets, and get them in line with each pair of pickets; the deflection-scale can be used to remedy any small lateral errors. The elevation is given by means of a gunner's quadrant or pointing-arc if available. If not, set a stake in front of the line of wheels and in rear of the muzzle, and immediately in the plane of sight, its height equal to the vertical distance from the top of the trunnion-sight to the ground; (for 3.2-inch gun 3′ 10".68; for 3.6-inch gun 3′ 11".16). Then give the rear sight the elevation corresponding to the range and aim at this point, using peep-and cross-hairs. An observer is necessary, and by means of his reports the necessary corrections are given until the elevation and length of fuze have been determined. After each shot care must be taken to run the gun up to the position it occupied before firing.

2d. In Firing at Troops in Ravines and Hollows when they cannot be seen from the battery select a stone or bush, or any distinguishable object, on the side of the ravine or hollow as an auxiliary target, and obtain the elevation and fuze for it; then by means of the lateral deviation of the sight change the direction of fire, and elevation and fuze if necessary. In such a case an observer on the flank or some commanding position is absolutely necessary.

3d. By Means of a Compass.—Select a distant auxiliary mark that can be seen from the gun; from a position as near the gun as possible obtain the angle between the auxiliary mark and the object; construct this angle at the gun and mark the position of the wheels; give elevation as previously explained, and make corrections by reports from an observer. The Germans have a device for measuring this angle: it consists practically of a horizontal graduated arc bearing an arm containing two vertical sights. It is placed on the gun, set at the angle indicated by the compass, and the gunner sights at the auxiliary object.

NIGHT-FIRING.

For night firing, or when there is much fog, a luminous aiming-point is required. This may be readily obtained by the use of a bull's-eye lantern. Soften the light by placing paper or other material over the glass, and draw thereon two right lines intersecting at right angles at the centre of the glass. At a convenient distance in front of the gun and in the plane of fire place the lantern on a post so that the point of intersection of the lines shall be at such a height that when the rear sight is at zero, and the axis of the gun horizontal, it can be directly aimed at. Establish a plumb-line between the lantern and the gun so that the plumb-line, the point of intersection of the lines on the lantern, and the object aimed at are in the same vertical plane. (The above requirements must of course be completed during the day, when the object can be seen.) Give the rear sight the elevation corresponding to the range, and aim at the point where the plumb-line covers the point of intersection of the two lines on the glass of the lantern.

If a gunner's quadrant or pointing-arc be available, simply determine and mark accurately the direction for each piece, and give elevation by either instrument.