Direction for firing in field artillery
In 1915 the Artillery Inspection published a new Наставление за стрелбата въ полската артилерия въ боя (Direction for firing in field artillery), which introduced some substantial changes in the direction published in 1908, based on the lessons learned from the Balkan wars. It was It contains instructions for firing with all types of artillery that could be used in a field combat, including those that Bulgaria did not yet have, i.e. :
1) light field and horse guns;
2) mountain guns and howitzers;
3) light and heavy field howitzers;
4) heavy field guns.
The direction includes six sections :
I. Ballistic data concerning guns.
II. Action of the projectiles
III. Measure of the dispersion and calculation of the corrections for shrapnel fire.
IV. Preparation of fire : determination of the range, laying the gun, direction of fire from covered positions, measure of the angle of site, observation of the bursts, perspective sketches.
V. Determination of the primary data, fire for adjustment and fire for effect.
VI. Fire practice : demonstrative, training and fighting fire. Instructions for writing firing reports.
In addition, an appendix contains an Instruction for observing the artillery fire from aircraft that reflects the experiences conducted during the siege of Odrin.
The direction includes also a firing table for both 75mm Schneider M. 1904 and Krupp M. 1910 guns, containing data up to 8100 m, while the table published in 1908 only went up to 6000 m.
Trajectories. The introduction and the first section are the same as the corresponding parts of the 1908 direction. The only addition is a discussion of the firing trajectories : trajectories in which the distance of 4000 m is reached with an elevation angle not exceeding 12°, are sloping, such as those of the light and heavy field guns, trajectories in which this distance is reached with an elevation angle greater than 12°, such as those of mountain guns and howitzers, are curved. To obtain a more curved trajectory for the same weight of the projectile and for the same distance it is necessary to reduce the muzzle velocity and the battering charge.
Since the guns have only one charge, they could fire at a single trajectory. The howitzers have several charges (from 3 to 7) and at the same distance, they can fire, according to need, with different trajectories. So selecting the distance and the corresponding charge, the howitzer can obtain an angle of descent up to 48° and an angle of vertical dispersion up to 60° with shrapnel and up to 200° for H.E. shell.
At all distances the greater the dispersion in height and width, the more sloping the trajectory. Dispersion in length is not always greater for curved trajectories. The effective area in length is as much larger as the trajectory is sloping. With the same muzzle velocity and weight of the projectile, a greater curvature of the trajectory can be obtained when the tip of the projectile is shaped to meet greater air resistance
Field howitzers. The field howitzers are specially assigned to destroy the dugouts of the field fortifications, to destroy the material of the enemy artillery, to destroy buildings and to fire on live targets behind artificial shelters and in the steep folds of the ground. They can be used together with field guns for shelling animate targets in the open, for firing against shield artillery and for destroying any kind of inanimate targets. Enemy artillery is fired with mixed shells : shrapnel and torpedo shell or H.E. shell with curved trajectories. Torpedo shell can be uses also to fire at animate targets, especially when they are entrenched; its action, even if weak in terms of material damage, has strong moral effect on the enemy. Horizontal targets, such as the roofs of dugouts and weak casemates, are fired with torpedo shell and the most curved trajectory for the distance. Also animate targets hidden behind artificial facilities - embankments, parapets, etc. - or in the folds of the area, are fired with curved trajectories, but with shrapnel or torpedo shell. Animate targets in the open and vertical inanimate targets (fencing walls, buildings, etc.) are fired with full charge - at close range with shrapnel or torpedo shell.
Universal shell. The universal shell has T&P fuze and can be used by field and mountain guns and by howitzers at any range and against any target. With time fire universal shell has the same effect as shrapnel, after the burst its head continues to move along its trajectory and, on impact, it bursts, scattering a great number of splinters that fly in all directions. Bursting, the head releases a red smoke, which makes adjusting easier. Hitting a shield or a weak wall, the heads burst into the barrier or very close behind it, hitting the nearby animate targets with their splinters. Firing at troops in trenches, the heads that hit the ridge of the rampart or the rear depression of the ditch burst and hit the shooters with their splinters. With high bursts, the heads fly more irregularly and some of them can turn and burst in the air before hitting the ground.
With percussion fuze the universal shell has a stronger effect than H.E. shells or common shells. Bursting it produces a visible smoke, more destruction on inanimate targets and more damage on animate targets. The fragments of cases and heads and some of the bullets fly forward and sideways with considerable energy. To repel close attacks, it is used as well as shrapnel, but its effect is stronger.
The effect of the universal shell of the 12cm howitzers is greater than that of the shrapnel, because the shrapnel action is strengthened by that of the head, which is larger, contains more explosive, and acts as a separate shell. However, against thick earthworks or strong armoured shelters, it cannot replace the torpedo shell.
The part relating to the other types of projectiles – shrapnel, H.E. shell for guns (бризантна граната), H.E. shell for howitzers (фугасна граната, previously called torpedo shell), common shell, case shot – does not change.
Shrapnel fire. The third section of the direction does not present substantial differences with respect to the text published in 1908, apart from some small corrections :
– the axes of the cone of the dispersion of the bullets at medium ranges is reduced from 300/50 m to 150/30 m;
– the normal height of burst for howitzer is set at 3/1000 to 7/1000, instead of 3/1000 to 6/1000;
– at a range of 2500 m and with an interval of burst of 50 m the average density of hits changes as follows : for light field and mountain guns 1.5, for heavy field guns 1.85, for howitzers 1.35;
– the area exposed to the shrapnel bullets for a skirmisher lying down is reduced to 0.15 m (previously 0.20).
In addition, the direction specifies that the height of burst of the shrapnel is estimated in millièmes of the distance, and the interval of burst in meters.
Preparation of fire. The primary firing data, that must be determined, are : 1) range, 2) deflection, 3) angle of sight – for indirect laying, 4) corrector – for time fire, 5) width, depth and kind of the target.
The range to the target can be measured on the map, obtained by telemeter, battery telescope or field glasses, estimated by eye or by sound, as in the previous direction. The range according with the effectiveness of the fire is considered : up to 1500 m close, from 1500 m to 4000 m mid, more than 4000 m great (the previous direction distinguished the case of field guns from that of mountain guns and gave slightly different data).
As regards the angle of sight, the direction explains how to determinate it, not only with the Schneider battery telescope, in use in the Bulgarian artillery since 1904, but also with the Goerz panorama sight and with the Krupp battery telescope, introduced only after the Balkan wars.
The remaining part of this section does not present any substantial differences, with the exception of the addition of a large section on gun laying in general and from an open position.
Gun laying. When the battery is laid at an target, the lines of fire of its guns form a sheaf, which can be:
1) concentric (съсредочен) if the lines of fire converge around a point in front of the battery. Up to the point of convergence, the firing lines and the bursts converge and are in the same order as the guns, at the point of convergence they come together, and further they cross and walk, the bursts being in the reverse order of the guns. In this case, the width of the front on which the bursts occur increases as you goe along. In the crossfire, the direction, distribution and transfer of fire is quite difficult.
When the auxiliary aiming point is located between the target and the battery : a) if the aiming point (A) is closer to the battery (B) than to the target (T), the cross at the target will be greater than the front of the battery (ex. 1); b) if the aiming point is half the distance to the target, or closer to the target, the crossing is equal to or less than the front (ex. 2-3); c) if the aiming point is behind the target, the bursts at the target are in a regular order and on a narrower front than that of the battery (ex. 4).
2) walking (разходяш) if the extended lines of fire converge around a point behind the battery. The sheaf of the beaten front is larger than that of the battery and increases with increasing firing range. The bursts order remains the same as the guns. The collection of the sheaf and the correction of direction can be done easily (ex. 5). The further the aiming point is moved back from the battery, the front width is reduced.
3) parallel (успореден) when the firing lines are closely parallel to each other. At all distances, the bursts are as wide as the front and in proper order. It occurs when the guns are aimed in parallel directions or at very distant aiming points (30 km or more), in front of or behind the battery (ex. 6). When needed, it can be easily moved, expanded and narrowed.
An auxiliary aiming point located on the side of the battery has the same properties as the corresponding aiming point located in the direction of the battery and the target.
Laying from an open position. If the target is clearly visible, the battery should fire directly at the target, because each gun lays directly at the sector opposite it and all have the same deflection. It is not clearly visible or its position is difficult to indicate to the battery, it is preferable to lay with the aid of an auxiliary aiming point. In any case, the first laying of the guns should be always done directly at the target.
If a battery commander sees that the target is not understood correctly, he gives additional explanations, or assigns an auxiliary aiming point for the whole battery. If he sees that the fire is not properly distributed along the front of the target, he orders the platoon commanders to change the laying of their guns.
Against dangerous targets close to the battery, each gun commander selects and assigns a section for his gun from the front of the target opposite him. When he considers that this section is sufficiently hit, he transfers the fire of his gun to one of the adjacent sections.
Laying from a masked or a covered position. In this case, laying is always done with the aid of an auxiliary aiming point and the elevation is given with the level or the quadrant. To lay the guns, it is necessary to locate the approximate position of the battery, to select an auxiliary aiming point, to determine the auxiliary angle and the correction, and to lay the guns at the target. Laying can be done simultaneously or sequentially, normally by means of the battery tube according with the rules established in the previous direction.
Observation of the bursts. The observations are done with the help of binoculars and if they are difficult, an auxiliary observer must be sent. However, when there is the possibility of large errors in direction, it is best to look at the first few shots with the naked eye, as they can occur outside the field of view of the binoculars. To accurately estimate the lateral deflections of the shells, the observer must be close to the firing battery.
As for the rules for the observation of the fire, the directive introduces only two addition on time fire :
– for the universal shell the trajectory can be judged by the fall of the heads in all not very high burst;
– when the observation point is much higher than the target, the heights of the bursts are shown slightly less than the actual ones, especially if the distance is not great.
Perspective sketch. This section of the direction does not present any particular innovations regarding the preparation of the sketches, while it slightly changes the way in which they are used to direct the fire, or to transmit what was seen from the observation post with them, saying that it is necessary :
a) to indicate the number or the name of the point around which a target appeared;
b) to show how far to the right or to the left of that point the target right flank is and what the target is;
c) to give the width of the front of the target in millièmes;
d) to give the distance to the target or its distance from here or there from the specified point.