Direction for firing in field and mountain QF artillery

 

 

0S75mmQF_4

 

 

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 dealt with the quick-firing guns, but gave also some instructions about the employment of the old not quick-firing guns on the new conditions. It included 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.    Kinds of fires : demonstrative, training and fighting fire. Instructions for writing firing reports.

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

 

Generalities rules. The artillery took 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, did 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 should begin as far as the objectives appeared, and consequently the process of adjustment should be shortened as much as possible. The Direction did 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.

 

Projectiles. The Direction examined all kinds of projectiles employed both by quick-firing and not quick-firing guns, describing in detail their main features and their effects. It considered 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 built 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 was regarded as the main projectile of field and mountain artillery against all animate targets that were not under cover. It contained about 300 lead bullets (200 for mountain guns), that, spreading out from the point of burst in the air, formed a sheaf and covered a space of considerable width and depth. Consequently shrapnel fire did not demand a complete adjustment, being sufficient to approximate to the target. In addition shrapnel contained a smoke-producing composition called colophan to make the burst more visible and facilitate the adjustment. This characteristic could be used also for tactical purposes. The rapid fire of a quick-firing battery with smoke-producing shrapnel made a dense cloud of smoke in front of the enemy line, preventing him from taking an effective aim or protecting the attacking troops. Shrapnel was equipped with a double action fuze, which permitted not only to change at will the point of burst (time fire), but also to burst on graze (percussion fire).

When the shrapnel burst, the body fell 10-20 m from the point of burst, usually showing the area of maximum effect. It served as a small solid shot that might destroy little obstacles. The fuze fell where unexploded shrapnel would fall; the diaphragm and the central tube fell near the fuze. If the fuze did not destroy itself on impact, the enemy might be able to know at what distance the firing battery was placed looking at its setting. The bullets were thrown forward, moving sideward, downward and upward along the trajectory of the projectile and, falling down, formed an elliptical cone of dispersion, whose axes at medium ranges were 300 m and 50 m long respectively. The bursting charge gave the bullets an additional velocity of 60-80 m, increasing their striking force. The bullets were not distributed uniformly on the beaten zone, but concentrated in a narrower area, called area of maximum effect. Their dispersion resulted from the height of burst and the range, while their lethal effect depended on their striking force and the density of the hits. The average density of hits was the number of hits upon a surface 1 sq. m and was 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 was 2.

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

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

    105mm QF field howitzer 1;

    mountain guns 0.5.

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

 

Percussion high explosive shell was 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 could be used at short ranges against infantry or cavalry attacks. It obtained the best effect when hit the gun shield or the ammunition wagon. It was also employed to shell targets located immediately in the rear of parapets, since when it burst the splinters struck vertically downwards, killing the men behind the shelter. Its effect depended upon the range and the nature of the ground : the more the ground was compact, the greater was the effect of the explosion. It should never be employed at great or medium range and with soft ground, since it buried itself in the soil and a large part of the explosive effect was dissipated.

 

HE shell fire

 

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

 

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

 

Field howitzer shrapnel had almost the same action of gun shrapnel, the main differences were :

    the interval of burst should be lower, since its trajectory was steeper;

    the density of hits was greater and the beaten area wider, since it contained more bullets;

    the power of penetration of the bullets was greater, since they were heavier.

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

 

Common shell was used only by not quick-firing guns against animate and inanimate targets. Against shielded guns it was preferred to the shrapnel. Against animate targets at mid range, it was effective when it burst 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 could be little greater, increasing up to 30 m. Against wide animate targets it was employed only out of the sphere of action of the shrapnel. At mid ranges it could pierce an earthwork 2 m thick, a brickwork 0.75 m thick, and a wooden palisade 0.35 m thick. It could destroy every kind of stone wall that might be meet in the battlefield.

 

Case shot 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 had 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 was replaced by shrapnel, which burst approximately 100 m in front of the gun when the fuze was set at zero, and approximately 150 m in front of the gun when it was set at 0.3 seconds.

 

Shrapnel fire. Shrapnel adopted by Bulgaria, like all the shrapnel employed at the beginning of 19th Century, had base charge with a sheaf of moderate angle of spread. At 1000 m it was 14° for field guns, 20° for mountain guns and 24° for field howitzers, with an increase of 1° every 500 m. The shrapnel produced 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 covered an area 300 m length and 50 m wide, but the heaviest losses were obtained within an area 50 m length and 30 m wide. The effective zone, i.d. the area within the bullets could inflict losses, was 100 m length and 30 m wide. The shrapnel was effective, if the bullets which reached the target had sufficient striking force and their number per unit of surface did 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 was on horseback. Experiments carried out in many countries had shown that the bullets lost 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 was 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 became less effective, since the velocity of the bullets decreased and, with it, their striking power; the trajectory became steeper and the bullets could not ricochet on the terrain; the combustion of the fuze became less regular; the extent of the effective area decreased. The greater effect was obtained up to 3000 m. Against uncovered animated targets shrapnel fire was 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 was under cover the projectile should fall near the target, otherwise it would hit the shelter and would 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 was 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 produced 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, should be carefully set, since shrapnel were really effective only if they burst close to the target : the greater was the interval of burst, the greater was the dispersion of bullets, the less the density, and consequently the smaller the number of hits. The normal interval of burst was put 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 was regarded as satisfactory. The interval should be reduced with the increase of the range, to take the target within the area of maximum effect. Great intervals were 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 were preferred.

The height of burst, i.e. the vertical distance of the point of burst above the horizon, should be carefully adjusted, taking into account that the combustion of the fuze was not always uniform. A probable deviation of 25 m was regarded as acceptable, but sometimes shrapnel burst on graze though the fire had been well adjusted. The lower was the height of burst, the smaller was the surface of covered by the sheaf. For field guns a height of 3/1000 of the range was adopted as the most favourable mean height of burst, while for mountain guns and howitzers it was usually set at 5/1000. At medium ranges they gave approximately the desired density of hits over the target, but at close ranges they were excessive, since the front covered increased largely and the density of hits decreased. Similarly, at long ranges they were insufficient. Therefore the normal height of burst varied 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 increased with the size of the targets : the greatest was their surface, the more vulnerable they were. The density of hits required to hit a target could be easily obtained, knowing the area of surface exposed, which, according with the estimate of that time, were as follows :

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

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

2)    skirmisher, standing – 0,4 sq. m;

skirmisher, kneeling – 0,3 m;

skirmisher, lying down – 0,20 m;

skirmisher, covered – 0,05 m.

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

Shrapnel fire was ineffective against troops under cover, i.e. located immediately in rear of parapets or any kind of obstacle, since behind them there was a blank space, where the bullets could not penetrate or were powerless and ineffective. The depth of the blank space could 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 was 8 m, firing at 4000 m it was only 3 m.

 

Shrapnel fuze correction. Shrapnel usually employed the double-action delay fuze. With quick-firing field guns the fuze was adjusted mechanically with a special fuze-setter, while with not quick-firing guns it was set manually. For quick-firing field guns the fuze was 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 was graduated in millièmes and afforded 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 made a corresponding increase of 100 m in the height of burst, and vice versa. Atmospheric conditions affected the correction: if the weather was warm, windless and fair the correction should be reduced by 1-2 millièmes, if it weather was damp, windy and snowy it should be increased in equal measure. Likewise every variation of 8 mm in the barometrical pressure required a correction of 1 millième. For quick-firing field guns firing at rangers greater than 2000 m the correction was increased of 1 millième every 500 m. Fire for adjustment was made 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 should 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 could 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 focused 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 should be always measured by rangefinder. For this purpose every line officer and every senior NCO should be trained to use it.

The range according with the effectiveness of the fire were :

    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 was necessary to overcome the effects of wind and drift. With moderate winds the deflection should 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 should be increased by 1 sight graduation in the direction of the upper wheel, with mountain guns by 2 sight graduations.

When the guns were placed in masked or covered positions, before firing, the battery commander had to determine the angle of sight. It could be measured by the battery telescope, by means of the sight and quadrant, by means of the graduated ruler, calculated on the map or obtained through theoretical formulas.

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

Since nearly all kinds of objects might 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 should be distributed and adapted to the main features of each of them.

Finally the Direction explained how to prepare perspective sketch, that could 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 was 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.