Direction for firing in field and mountain QF artillery

 

 

 

 

The rearmament of the Bulgarian artillery with modern quick-firing guns, occurred in 1904, required the introduction of new firing rules to replace those published only two years before, in 1902. In 1905 a Наставление за стрелбата въ полската и планинската скорострелна артилерия (Direction for firing in field and mountain quick-firing artillery) was published, adapting the text of the French Réglement de manoeuvre de l’artillerie de campagne published on 8 June 1903. Writing the text of the Direction the head of the Technical department of the Artillery Inspection, col. Kalin Naydenov, could not rely on data derived from practical experiences, since at that time not even a single quick-firing gun had arrived in Bulgaria. The only information available was the notes of the head of the Administrative department, lt.col. Vladimir Vazov, who had been sent to Poitiers, in France, to gain experience.

Between 1905 and 1908 the new guns were intensively tested and finally the revised standard version of the Наставление за стрелбата въ полската и планинската скорострелна артилерия was published in 1908, followed in 1909 by a detailed exposition written by col. Kalin Naydenov (Новото наставление на стрлбата в полската и планинската артилерия на практика, Sofia 1909), that covered only the first four section of the Direction.

 

Basically the direction deals with the quick-firing guns, but gives also some instructions about the employment of the old not quick-firing guns on the new conditions. It includes five sections :

I.     Ballistic data concerning guns and projectiles.

II.   Measure of the dispersion and calculation of the corrections for shrapnel fire.

III.  Preparation of fire : determination of the range, direction of fire from covered positions, measure of the angle of site, observation of the bursts.

IV.  Determination of the primary data, fire for adjustment and fire for effect.

V.    Fire practice : demonstrative, training and fighting fire. Instructions for writing firing reports.

The direction includes also the firing tables of all kinds of field and mountain guns adopted by the Bulgarian artillery.

 

Generalities. The artillery takes part in the combat only with its fire. Quick-firing artillery shoot to break down any resistance with a rapid and powerful fire of short duration from opportune and well chosen positions at the most important targets in a particular moment. With the enormous increase in fire effect due to the introduction of magazine rifles and quick-firing artillery, troops, and especially infantry, do not expose themselves except for a very short time to the artillery fire, utilizing to the utmost all available cover. To succeed, the fire for effect must begin as far as the objectives appeared, and consequently the process of adjustment must be shortened as much as possible. The Direction does not prescribed precise ranging against a definite target, but to cover a considerable extent with shrapnel bullets, to block every attempt to every object to move about or remain there uncovered, without being put out of action.

 

Field howitzers. The field howitzers shoot relatively heavy projectiles with low initial velocities, so that their trajectories are more curve. With the same weight of projectile, they use several charges smaller than each other, which give trajectories for the same distance, more curved than each other, and therefore with greater angles of incidence. This makes possible, by selecting the distance and the corresponding charge, to obtain an angle of incidence from 40° to 48° and an angle of dispersion of up to 60°.

The field howitzers are specially assigned to destroy the dugouts of the field fortifications and to fire on live targets behind artificial shelters and in the steep folds of the ground, because this kind of targets requires more curved trajectories and more powerful projectiles. 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.

At exposed live targets and at vertical inanimate targets, howitzers fire at full charge, in the first case even at long range. To hit live targets howitzers use shrapnel, while to destroy inanimate targets torpedo shells.

 

Projectiles. The Direction examines all kinds of projectiles employed both by quick-firing and not quick-firing guns, describing in detail their main features and their effects. It considers also the projectiles fired by 120mm not quick-firing howitzers assigned to the heavy field artillery, and by the 105mm quick-firing light field howitzer, that at that time the Bulgarian Army intended to buy in France. At that time the 120mm not quick-firing howitzer was equipped only with shrapnel and common shells, but later it received also Schneider built torpedo shells.

 

Time shrapnel is regarded as the main projectile of field and mountain artillery against all animate targets that are not under cover. It contains about 300 lead bullets (200 for mountain guns), that, spreading out from the point of burst in the air, form a sheaf and cover a space of considerable width and depth. Consequently, shrapnel fire does not demand a complete adjustment, being sufficient to approximate to the target. In addition, shrapnel contains a smoke-producing composition called colophan to make the burst more visible and facilitate the adjustment. This characteristic can be used also for tactical purposes. The rapid fire of a quick-firing battery with smoke-producing shrapnel makes a dense cloud of smoke in front of the enemy line, preventing him from taking an effective aim or protecting the attacking troops. Shrapnel is equipped with a double action fuze, which permitts not only to change at will the point of burst (time fire), but also to burst on graze (percussion fire).

When the shrapnel bursts, the body falls 10-20 m from the point of burst, usually showing the area of maximum effect. It serves as a small solid shot that may destroy little obstacles. The fuze falls where unexploded shrapnel will fall, the diaphragm and the central tube fall near the fuze. If the fuze does not destroy itself on impact, the enemy may be able to know at what distance the firing battery is placed looking at its setting. The bullets are thrown forward, moving sideward, downward and upward along the trajectory of the projectile and, falling down, form an elliptical cone of dispersion, whose axes at medium ranges are 300 m and 50 m long respectively. The bursting charge gives the bullets an additional velocity of 60-80 m, increasing their striking force. The bullets are not distributed uniformly on the beaten zone, but concentrated in a narrower area, called area of maximum effect. Their dispersion results from the height of burst and the range, while their lethal effect depends on their striking force and the density of the hits. The average density of hits is the number of hits upon a surface 1 sq. m and is derived by dividing the total number of hits by the beaten area in square meters : for instance, with an area of 50 sq. m hit by 100 bullets, the average density of hits is 2.

At a range of 2500 m and with an interval of burst of 50 m, the average density of hit is :

–    75mm QF and 87mm not QF field guns 1.5;

–    105mm QF field howitzer 1;

–    mountain guns 0.5.

 

Percussion shrapnel usually bursts after having hitting the ground or having ricocheting. In this way, it changes a little its direction and greatly reduces its final velocity and therefore the living force of the bullets. Against animate targets it is less effective than time shrapnel, but it can destroy small inanimate targets like bridges, thin walls, fences, light shelter. It can be used against shielded artillery, when high explosive shells are lacking.

 

Percussion high explosive shell is used either against shielded batteries at a range of 2500 m at most, or to wreck covers and buildings (houses, bridges, walls, wooden palisades, field fortifications, thin shelters). It can be used at short ranges against infantry or cavalry attacks. It obtains the best effect when hit the gun shield or the ammunition wagon. It is also employed to shell targets located immediately in the rear of parapets, since when it bursts the splinters struck vertically downwards, killing the men behind the shelter. Its effect depends upon the range and the nature of the ground : the more the ground is compact, the greater is the effect of the explosion. It must be never employed at great or medium range and with soft ground, since it buries itself in the soil and a large part of the explosive effect is dissipated.

 

HE shell fire

 

Even at close range and with hard ground it requires a very careful adjustment, since its effect is very local. It can be successfully employed to harass the occupant of the hostile trenches, waiting the moment when the troops are forced to man their parapets. Having a very sensitive fuze the H.E. shell bursts as soon as hit the ground, without ricocheting, making two cones of dispersion : the lower one hits the target, while the upper one scatters upward and is almost inoffensive. The angle of the cone of dispersion is between 110°-140°. The explosion gives a very great number of splinters (even 500-700), which, reaching a very high speed (up to 600 m/s), can inflict disabling wounds, if the target is at 30-40 paces. Their action in deep, however, is small and at a distance of more than 50 paces from the bursting point, they are almost useless.

 

Torpedo shell is the most powerful projectile of the field artillery. It is employed by the field howitzers to destroy every kind of inanimate targets. It is equipped with a delay-action fuze, when it must penetrate the roof of splinters proof before exploding, but it is equipped with a simple percussion fuze when it must explode on impact. It is able to mess up earthworks, destroy armoured shelters and sound buildings and sweep away every kind of obstacle that might meet with on the battlefield. The most powerful effect is produced when it falls at an angle greater than 30° on a stiff ground. In this case, it makes a crater 1 m deep and about 3 m in diameter. To shell trenches or armoured shelters the trajectory must be steep, therefore the howitzers employ the low charge. At a range of less than 2000 m they can be used also against shielded artillery, but are less effective than field guns loaded with H.E. shells, since it is not easy for howitzers to hit the shield, having a steeper trajectory. Torpedo shell has also a terrible moral effect, since bursting it produces a thundering crash that has a tremendous effect on the nerves of the troops.

 

Field howitzer shrapnel has almost the same action of gun shrapnel, the main differences are :

–    the interval of burst must be lower, since its trajectory is steeper;

–    the density of hits is greater and the beaten area wider, since it contains more bullets;

–    the power of penetration of the bullets is greater, since they are heavier.

Firing at uncovered animate targets, the howitzers employ the full charge to obtain a sloping trajectory, on the contrary, firing at troops under cover, they employ the low charge to obtain a steep trajectory.

 

Common shell is used only by not quick-firing guns against animate and inanimate targets. Against shielded guns it is preferred to the shrapnel. Against animate targets at mid range, it is effective when it bursts no more than 20 m in front of the target and no more than 3-4 m behind it. At close range and against high targets, the extent of the area of burst can be little greater, increasing up to 30 m. Against wide animate targets it is employed only out of the sphere of action of the shrapnel. At mid ranges it can pierce an earthwork 2 m thick, a brickwork 0.75 m thick, and a wooden palisade 0.35 m thick. It can destroy every kind of stone wall that may be meet in the battlefield.

 

Case shot is used only by not quick-firing guns to beat off close attacks at a range of 400 m at most. The cone of dispersion of the balls has an angle of opening of 6° with an axis of dispersion of 1/10 of the length and a range of only 400 – 500 m. With quick-firing guns, it is replaced by shrapnel, which bursts approximately 100 m in front of the gun when the fuze is set at zero, and approximately 150 m in front of the gun when it is set at 0.3 seconds.

 

Shrapnel fire. Shrapnel adopted by Bulgaria, like all the shrapnel employed at the beginning of 19th Century, has base charge with a sheaf of moderate angle of spread. At 1000 m it is 14° for field guns, 20° for mountain guns and 24° for field howitzers, with an increase of 1° every 500 m. The shrapnel produces the best effect within a range of 1000-3000 m, with an interval of burst of 30-100 m (up to 150 m at close ranges) and a height of burst of 3/1000 of the range for field guns and 5/1000 for mountain guns. On these conditions the cone of dispersion covers an area 300 m length and 50 m wide, but the heaviest losses are obtained within an area 50 m length and 30 m wide. The effective zone, i.d. the area within the bullets can inflict losses, was 100 m length and 30 m wide. The shrapnel is effective, if the bullets, which reach the target, have sufficient striking force and their number per unit of surface does not fall below a certain figure. To remove a man from the ranks, the bullets must have a living force of at least 8-13 kgm, or also 19 kgm, if he is on horseback. Experiments carried out in many countries have shown that the bullets lose quickly their energy after the opening of the shrapnel, becoming ineffective at about 150-200 m from the point of burst. The following picture shows the size of the sheaf of dispersion and the distribution of the bullets of a shrapnel fired at a range of 3000 m with a normal height of burst.

 

Shrapnel_cone of dispersion S

 

The effect of shrapnel fire is somehow affected by the range, the interval of burst, the height of burst, the size of the targets, the ground and the shelters.

Increasing the range, the shrapnel fire becomes less effective, since the velocity of the bullets decreases and, with it, their striking power; the trajectory becomes steeper and the bullets cannot ricochet on the terrain; the combustion of the fuze becomes less regular; the extent of the effective area decreases. The greater effect is obtained up to 3000 m. Against uncovered animated targets shrapnel fire is regarded as satisfactory even with an error in range of 50 m in front the target or 30 m behind it (with quick firing guns at range less than 2000 m even 50 m behind the target), but if the enemy is under cover the projectile must fall near the target, otherwise it will hit the shelter and will not be able to inflict losses. The following figure shows the effective area of the cone of dispersion of the bullets of shrapnel fired with a normal height of burst at different ranges. At close ranges, less than 400-500 m the shrapnel is employed with fuze set at zero.

 

Shrapnel_effect of range S

 

Shrapnel bursting too far in front of the target and those bursting in the air above the target produce little of no effect. Therefore the interval of burst of the shrapnel, i.e. the horizontal distance between the point of burst and the target, must be carefully set, since shrapnel are really effective only if they burst close to the target : the greater is the interval of burst, the greater is the dispersion of bullets, the less the density, and consequently the smaller the number of hits. The normal interval of burst is det at 30-100 m at medium ranges (up to 3000 m), but at close ranges (less than 1500 m) even an interval of 150 m is regarded as satisfactory. The interval must be reduced with the increase of the range, to take the target within the area of maximum effect. Great intervals are required to obtain a broad dispersion when firing at thin targets at close ranges or shooting a wide front, while at great ranges or with targets deployed in depth or on a short front, small intervals are preferred.

The height of burst, i.e. the vertical distance of the point of burst above the horizon, must be carefully adjusted, taking into account that the combustion of the fuze is not always uniform. A probable deviation of 25 m is regarded as acceptable, but sometimes shrapnel bursts on graze though the fire has been well adjusted. The lower is the height of burst; the smaller is the surface of covered by the sheaf. For field guns a height of 3/1000 of the range is adopted as the most favourable mean height of burst, while for mountain guns and howitzers it is usually set at 5/1000. At medium ranges, they give approximately the desired density of hits over the target, but at close ranges they are excessive, since the front covered increases largely and the density of hits decreases. Similarly, at long ranges they are insufficient. Therefore the normal height of burst varies from 2/1000 to 4/1000 for field guns and 3/1000 to 6/1000 for mountain guns and howitzers.

The effect of shrapnel fire increases with the size of the targets : the greatest is their surface, the more vulnerable they are. The density of hits requires to hit a target can be easily obtained, knowing the area of the surface exposed, which, according with the estimate of that time, are as follows :

1)       horse and rider, side view – 1.8 sq. m;

horse and rider, front view – 1.2 sq. m;

2)    skirmisher, standing, front view – 0.4 sq. m;

skirmisher, standing, side view – 0.3 sq. m;

skirmisher, kneeling, side view – 0.3 m;

skirmisher, lying down – 0.20 m;

skirmisher, covered – 0.05 m.

To hit a animate target, the imaginary vertical surface in which it is located must to be covered with such a density that one bullet falls on each part of the quadrant meter represented by the target. Thus, to hit a standing infantryman it is required a density of 2.5, to hit a kneeling skirmisher behind a parapet a density of 20.

To make a unit unable to continue fighting, it is enough to put out of order in a short time 50% of its men. For this, it is sufficient if the fire continues until a specific density is obtained for the various targets :

–         cavalry : 0.5

–         infantry, standing : 1.0

–         infantry, lying down : 1.5

–         infantry, uncovered : 2.5

–         infantry, behind a parapet : 10.0

Since shrapnel bursts in air, the effect of time fire depends less upon the character of the terrain than any other kind of projectile. Nevertheless it has some influence. Indeed, if the terrain in front of the target is level and hard, the bullets will ricochet easily and loose little of their velocity, being able to produce still effective hits. But if it is broken or soft, the majority of the bullets will imbed themselves in the ground. The same happens when the slope of ground is rising at the target. In addition, the width of the cone of dispersion is greatest when the slope of the ground is equal to the angle of fall of the unexploded shrapnel. As the slope of the ground increases, the width of the zone of dispersion decreases. When the slope of the ground is greater that the angle of fall of the lowest bullet, no effect is produced at all.

Shrapnel fire is ineffective against troops under cover, i.e. located immediately in rear of parapets or any kind of obstacle, since behind them there is a blank space, where the bullets cannot penetrate or are powerless and ineffective. The depth of the blank space can be calculated multiplying the height of the cover by 8, 6, 4, 3 for ranges of 1, 2, 3, 4 km respectively. The closer the range, the most sloping the trajectory, the broadest the blank space : with a cover 1 m high, firing at 1000 m the blank space is 8 m, firing at 4000 m it is only 3 m.

 

Shrapnel fuze correction. Shrapnel usually employs the double-action delay fuze. With quick-firing field guns, the fuze is adjusted mechanically with a special fuze-setter, while with not quick-firing guns it is set manually. For quick-firing field guns, the fuze is calibrated with a height of 300 m on the sea level, for quick-firing mountain guns at 1000 m, and for not quick-firing guns for a height close to the sea level. The corrector scale of the fuze setter is graduated in millièmes and affords a method of making slight changes in the point of burst of the shrapnel. As a rule, an increase of 1 millième in the corrector setting makes a corresponding increase of 100 m in the height of burst, and vice versa. Atmospheric conditions affect the correction: if the weather is warm, windless and fair the correction must be reduced by 1-2 millièmes, if it weather is damp, windy and snowy it must be increased in equal measure. Likewise every variation of 8 mm in the barometrical pressure requires a correction of 1 millième. For quick-firing field guns firing at ranges greater than 2000 m the correction is increased of 1 millième every 500 m. Fire for adjustment is done with low bursts, reducing the corresponding correction by 2 millièmes at medium ranges, by 5 millième at close ranges.

 

Preparation of fire. The primary firing data, that must be determined, were : 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 a map, or obtained by telemeter, battery telescope or field glasses, or estimated by eye or by sound. While previously the distance was estimated mainly by eye, this Direction focuses its attention to the use of the rangefinder. When it was published the Bulgarian Army employed mainly the Souchier prismatic telemeter, adopted also by the Russian Army, but the Goerz rangefinder 1 m base was ordered in 1909. Firing at medium and long range, the distance must be always measured by rangefinder. For this purpose every line officer and every senior NCO must be trained to use it.

The range according with the effectiveness of the fire are :

–    for field guns: up to 1500 m close, from 1500 m to 3500 m mid, more than 3500 m great;

–    for mountain guns: up to 1500 m close, from 1500 m to 3000 m mid, more than 3000 m great.

The correction in deflection is necessary to overcome the effects of wind and drift. With moderate winds the deflection must be changed, adding or subtracting 1 millième, depending upon the direction of the wind, 2 millièmes with strong winds. With field guns every 1000 m of distance and every 5 cm of difference in the position of the wheels the deflection must be increased by 1 sight graduation in the direction of the upper wheel, with mountain guns by 2 sight graduations.

When the guns are placed in masked or covered positions, before firing, the battery commander must determine the angle of sight. It can be measured by the battery telescope, by means of the sight and quadrant, by means of the graduated ruler (reglette de direction, calculated on the map or through theoretical formulas.

The corrector is used to fix the height of burst of time-fuzed shrapnel, as shown above.

Since nearly all kinds of objects may be the target of the artillery fire – infantry, cavalry and artillery in many different formations, field fortifications, bridges, buildings, woods, balloon etc. – to be really effective the fire must be distributed and adapted to the main features of each of them.

The firing tables contain all the data for producing fire and calculating the corrections of the shots in all the cases and for all distances over 100 m.

 

Observation of the bursts. The direction emphasizes that one of the main conditions for fast and accurate adjustment and fire is the correct observation of the bursts relative to the target. Since this can be obtained only with continuous and methodical training, all officers, warrant officers, and non-commissioned officers must be trained annually in observation, along with training in measuring and determining distances.

The observations are done with the help of binoculars and if they are difficult for one reason or another, an auxiliary observer must be sent.

 

Firing projectiles with percussion fuze, the bursts must be observed at the first appearance of the smoke, especially when the projectile falls close to the target or there is wind, taking into account that :

–    if the cloud of smoke and dust cover the target, the burst is in front of the target;

–    if the target is covered by some of the smoke and dust, the burst is beyond the target;

–    if the smoke appears on one side of the target and soon passes to the other, the burst is close to the target;

–    firing from high positions, or at targets placed on the steep side of the heights, the bursts from this side appear below the target, and the bursts from the other side above it;

–    shells falling on the target can be best recognized by the hit or movement produced in the target;

–    firing at an interrupted target (battery, infantry company deployed by platoons…) the bursts, which occurs in the intervals cannot be always determined with certainty, so only well-observed falls must be retained;

–    if the area around the target has gullies that hide the smoke from the bursts, the distance must be measured with maximum precision and the area plotted on the map;

–    shrapnel with T&P fuze bursts on impact as soon as it hits the ground; impact bursts differ from low time bursts by the shape of the smoke and by the fact that the smoke is often mixed with ground.

 

Firing shrapnel with time fuze, the bursts must be observed in four respects :

–    how high above the target the burst occurs;

–    where the bullets fall,

–    weather the burst is in front of or behind the target and how much, if it is possible to determine it;

–    the direction of the burst relative to the target.

The burst heights are measured on the millièmes scale of the binoculars or of the battery telescope, with the graduated ruler (only at close range) or by eye.  When the fuze is set at a distance greater than that of the target, the shrapnel falls in the ground. Therefore, the observer should be very careful not to mix it with the time burst: this case it was known by the finger that rises around the target before the burst and by the development of the smoke, which, in contrast to ordinary burst, occurs from the bottom up.

 

Perspective sketch. Finally the Direction explains how to prepare perspective sketch, that can be used to :

–    to easily orient the high commander, when they arrived at the position or at the observation post;

–    to direct and control the fire of an artillery division of a group of batteries, when its head is distant;

–    to offer to the battery commander information about the firing data related to different points of the battlefield;

–    to permit to the observers to show to the firing guns about the position of their targets.

To direct the fire according to the sketch, or to transmit what was seen from the observation post, it is necessary :

a)    to show the number 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;

c)    to show how far the target is from here or there from the indicated point;

d)    to give the width of the front of the target.

Determining the lateral distances (b), the approximate angular difference in the position of the batteries and the observation post should be taken into account.

According with these instructions, the battery commander lays the guns to the indicated point, and order to open fire, that is controlled by signals with flags.