Munitions are used for fulfilling the primary task of artillery, which is destruction or neutralization of enemy army, as well as enabling or supporting the ground maneuver by suppressing enemy defenses. First munitions were spherical stone projectiles, launched from ballistae and catapults. Identical projectiles were also used by first gunpowder artillery. Those were typically around 8 cm in diameter. French navy used basalt, which has higher density and hardness, to achieve increased hitting power; those projectiles could penetrate ship’s wooden sides at 200 meters. Stone projectiles were also used as incidendiary projectiles by coating them with lime, followed by resin. These were superseded by lead, which was easy to shape due to low melting point. In early 13th century (cca. 1221.), Chinese were using explosive ceramic projectiles, launched from catapult or a cannon. These were filled either with gunpowder, or a combination of gunpowder and metal shrapnel. In Europe, projectiles from bronze or iron were also used. These could be homogenous, or filled with gunpowder; earliest percussion fuzes – using flint to create the spark – appeared in 1650. Another type of shot was canister shot, which was used against combat for infantry at close range, and was particularly effective against linear formations of Middle and early New Ages. But when linear formations disappeared after American Civil War, canister shot was replaced by shrapnel, which utilizes time fuze and detonates in the air. During the 19th century, two main types of fuzes were used, time delay and impact fuzes. Time fuzes were combustion types, consisting of a burning fuse train, ignited upon firing. There were various designs, but all were only accurate to approximately the nearest 1/2 or 1/4 sec at best.
During twentieth century, and especially after World War II, development in materials science has significantly improved lethality of artillery munitions. During that time, first time and proximity fuzes appeared. However, percussion fuzes were still the primary fuze type in use.
At explosion, fragments fly away at sides and forward due to motion of the projectile. Unless projectile is descending at almost vertical path, this means that over 50% of fragments are uselessly lost either due to striking the ground or flying into the air. This is especially pronounced with strikes at soft ground. When projectile strikes hard ground, there is a significant possibility of fuze breaking off. Consequently, best way to utilize fragmentation projectiles is airburst. Doing so increases the quantity of useful fragments by 25% as well as allowing them to reach dug-in targets. This requires utilizing the fuze which will properly time the explosion so that it occurs at height of 5-15 meters, that is 0,02-0,06 seconds before striking the ground. Mechanical fuzes are not always precise enough, so proximity fuzes are preferred choice.
First proximity fuze was designed by the British. It relied on optics and was used only in rockets. Sensor measured amount of light entering it, which means that was effective only in broad daylight. First gun proximity fuze, made in 1944., used radiowave reflection from the target for activating explosives, and was developed by the US Navy for air defense purposes. Due to its high cost, mechanical fuzes predominated even after World War II. Other proximity fuzes can use lasers or microwaves in the same way, and more sophisticated versions measure distance from the target. In these variants, laser radiation is emitted in a circular fashon, to sides and slightly to the front relative to projectile’s axis.
Contact fuzes detonate the projectile at contact with target, so they are not a good choice for demolition or attacking armoured target. For these purposes, delayed-action fuzes are a preferred choice. They have a timed delay of 0,05 seconds after hitting the target, which allows the projectile to penetrate and explode within the target’s structure.
Modern fuzes can combine several functions. MOFA (Multi Option Fuze for Artillery) is a programmable all-purpose fuze for bursting ammunition. Options include impact detonation, delayed impact detonation, proximity detonation and time delay detonation. It is classified on NATO standard 105 mm and 155 mm projectiles.
Most typical munitions are high explosive munitions. Modern projectiles, contact or timed, produce around 2.000 fragments; 76 mm M48 mountain gun produces 2.300 fragments, of which lethal fragments are as follows: 80 fragments of 5-10 g weight, 30 fragments of 10-20 g weight, 10 fragments of 20-30 g weight, and one fragment each of 30-50 g, 50-100 g and 100-300 g, for a total of 123 fragments. Around 20% of fragments originate from the front part of the projectile, 70% from the cylindrical body and 10% from the rear part, which means that angle of impact is crucial.
Second large jump in munitions development was the appearance of submunitions. First submunitions (M35-M39) were only intended for use against soft targets, while series M42 and later have dual use against soft and hard targets. These submunitions weight around 230 g each with the explosive charge of 30 g. A 105 mm projectile has 18 submunitions, while a 227 mm rocket of a MLRS has 644 pieces. Total explosive content of a 155 mm M483 projectile is only 2,6 kg, far less than 6,6 kg in M107 or 11,3 kg in L15 high explosive projectiles. Bomblets are typically ejected at altitude of 350 meters, and cover an area 150 meters in diameter. They are effective against armour up to 65 mm of thickness, but due to utilization of contact fuze, uneven terrain significantly reduces their effectiveness against personnel. Since bomblet release is fairly noticeable, soldiers have several seconds after release to find cover.
In general, United States tend to focus on greater number of smaller bomblets, while Germany, Israel and Russia focus on smaller number of larger bomblets. Some Russian 152 mm munitions carry only eight bomblets, each weighting 1,4 kg with 230 g of explosives. Tactical missile warheads carry larger number of bomblets: 450 kg M251 warhead carries 860 BLU-230 bomblets, while 585 kg ATACMS warhead carries 950 600-gram M74 bomblets.
Sensory-activated submunitions were developed in 1970s in the US SADARM programme. Originally intended for 203 mm calibre, submunitions were instead developed for the 155 mm calibre munitions. In general, a 155 mm projectile carries 2-3 submunitions with cumulative charges. Submunitions are ejected from the carrier at altitude of around 1.000 meters, and activate a slowing device (parachute, winglets), which allows sensory systems to search the area below submunitions. Sensors can be millimetric radar, infrared sensors or a combination of the two. In the dual-sensor arrangement, radar is used for the target acquisition, while IR is used for validation and terminal guidance. Once target is detected and identified, from a height of 200 meters an explosively formed penetrator is fired. Such penetrator, formed through distortion of a concave metal plate under force of explosion, flies at 2000 m/s towards the target. After 100 m, optimal characteristics are achieved, and retained for another 200 meters. In this window, metallic penetrator wll penetrate the armour about as thick as the starting diameter of the metal disc which had formed it. Since top of the tank is typically underprotected, this type of attack is very effective. Typical materials for EFP are copper, tanalus and depleted uranium.
Other than conventional munitions, there are also chemical, biological and nuclear projectiles. Nuclear projectiles can achieve yields of 1-2 kt for howitzers of 155 / 203 mm calibre. Chemical projectiles filled with chlor were first used in World War I. Soon after, mustard gas was also utilized; it is still used in chemical projectiles. Another category are thermobaric, in particular fuel-air explosive shells. Due to using oxygen from the air, these have far greater effectiveness per unit of weight. While TNT contains 42% oxygen per weight, propelinoxyde gets 41% of oxygen necessary from the air, which means that for the same weight it releases 7,9 times more energy. Russian military has a large selection of FAE munitions, while Canadian military uses FAE FALLON system for clearing minefields. However, temperature and humidity can change the power of the explosion by 10-20%.
Subcalibre munitions are used for anti-tank combat. These are typically made from tungsten alloys, or from depleted uranium. DU has a disadvantage in producing cancerogenic dust, turning projectiles into de facto NBC weapons. Another type are HEAT (high-explosive antitank) projectiles, which only have a ballistic cap and explosives. Cumulative projectiles have explosives in the shape of a funnel, which directs hot gasses into focus and enables penetration up to 50 cm. These are typically equipped with stabilizers and a rotating ring as their effectiveness is reduced by rotation.
Special category are non-destructive munitions. These include star and smoke shells, which typically release submunitions through the bottom of the carrier shell. Star shell, or illuminating projectile, has flat bottom which doubles as a cover for a parachute and a glowing mass. Said cover and parachute are ejected by a black powder charge at at altitude of 400-600 meters. Star shells are used for night targeting and for disturbing the enemy.
Mortars typically have the same selection of munitions as the guns and howitzers do. Common calibres are 60, 82, 120 and 240 mm, with contact, smoke and star shells.
Maximum range of classical artillery shells depends primarily on the exit energy at the mouth of the barrel. This depends on projectile’s mass and energy produced by the propellant. Modern 105 mm munitions have kinetic energy of 11 MJ, 152-155 mm munitions around 20 MJ and 203-210 mm munitions around 49 MJ. Typically only around 1/3 of the chemical energy of charge is translated into projectile’s kinetic energy, and a lot depends on the barrel length and combustion chamber volume. A 52-calibre barrel with 23 l chamber allows maximum muzzle velocity of 945 m/s, and range of 30 km. (Range can also be increased by a longer barrel, but that is independent of the munitions themselves).
ERFB (extended range full bore ammunition) attempted to achieve increased range through aerodynamic design. However, compared to classical ammunition, ERFB has 1,7% less velocity, 5,7% greater mass, which leads to 1% increase in kinetic energy and less than 5% increase in range while carrying 23% smaller explosive charge. As meteorological conditions can affect the range of artillery by 10%, ERFB is not a good investment. Better option are rocket-assisted or base bleed projectiles. Base-bleed projectiles reduce air drag by providing a slow injection of gasses into low-pressure zone right behind the projectile. Both increase maximum range by 30%, but base-bleed projectiles suffer from reduced explosive power and longer projectile, while RAP have increased dispersion, unless guided. More modern base bleed and rocket assisted projectiles can have range twice the range of a normal projectile – PzH 2000 has range of 28-30 km with normal projectile, but this increases to 56-60 km with DENEL V-LAP active rocket projectile.
Issue of precision is particularly important for extended range projectiles as their longer time of flight also means greater susceptibility to influences such as cross winds and variations in atmospheric density. Consequently, large fraction of extended range projectiles are designed with submunition payloads. This also improves counter-battery fire ability as submunitions will blanket a wide area around enemy battery’s last known position.
Dispersion and precision
Main aim is to bring munitions as close as possible to target. There are several factors which can prevent this. First is target location error, where the target is not accurately located. Second one is discrepancy between intended point of impact and actual point of impact. Size of an area where munitions fall is described by the term dispersion.
Dispersion or accuracy is determined by three factors: discrepancy between calculated and actual muzzle exit velocity, inaccuracy in metereological data and inaccuracy in determining position of the artillery piece. While better computers and ballistic models can increase accuracy by some meters, main problem are atmospheric conditions, which vary across both distance and altitude. Incorrect or insufficient metereological data can cause inaccuracy of 10-20 m and 10 s at distances of 5 km. At 40 km, such deviations can exceed 200 meters and 100 seconds. To reduce these issues artillery utilizes metereological probes (balloons), several of which can create a fairly accurate picture. Compared to gun shells, rockets and missiles are particularly sensitive to side wind due to large control surfaces and dimensions of the projectile itself. For all of this accurate position of artillery pieces and other equipment has to be known, for which the best choice is the inertial system for determining location and azimuth, which appeared in 1970s. Combining INS with GPS system can significantly increase overall accuracy compared to what either system can achieve in isolation.
The greatest individual cause of innacuracy are fluctuations in the projectile muzzle velocity. As the barrel wears out, gas pressure falls and projectile muzzle velocity gets reduced. There are also differences between individual ammunition pieces due to temperature, production tolerances and other factors which affect rate of combustion. Through usage of modern radars, it is possible to follow and correct for the barrel wear and other factors, allowing prediction of muzzle velocity for each projectile and thus adequate corrections.
Projectile shape also has major influence on projectile precision. Norwegian manufacturer Nammo produces two 155 mm projectiles, US 155 mm M107 round and its own 155 mm HE round. Nammo’s HE Extended Range (HE-ER) round has more streamlined shape, reducing drag and increasing range. More importantly, Namo’s projectile is finely machined outside and inside before nosing, which reduces weight and run-out variation, thus reducing dispersion. When using 155 mm/39 cal ordnance, Nammo NM28, a variant of US M107 HE projectile, achieves deviation of +/-80 meters from the target at range of 20 km. Using the same gun and range, Nammo ‘s HE-ER round achieves deviation of 30 meters, similar to precision guidance kits for artillery rounds.
Smart munitions are incapable of maneuvering, which reduces effectiveness against mobile targets, such as tanks which can pass 300 meters during munitions’ descent. Conseqently, “intelligent”, terminally-guided munitions were designed. These munitions have the capacity of maneuver, and have very flat trajectory which increases the possibility of finding the target. However, due to increases in armour protection of many targets, number of submunitions in each warhead is being reduced. Sensors are also typically dual, such as mm radar and IR, combining radar’s bad weather performance and IR sensors’ resistance to jamming. Some munitions are guided to target by an external operator, through usage of laser targeting systems. Those are less maneuverable and limited by atmospheric conditions, but also far more versatile. The round flies most of the path in unguided mode, activating its seeker and acquiring the laser spot once it nears the target. Satellite-aided inertially guided rounds may offer greater flexibility than laser guided rounds. These are pre-programmed with target coordinates and use GPS system to roughly find the target, and laser for precise targeting. Accuracy is primarily limited by the aerodynamic and control system design and the type of satellite navigation technology used, and CEP for artillery shells is typically around 4,5 meters. However, significant errors may be caused by mistakes in inputting target coordinates, damage to computer systems of the rounds during transport or firing, as well as weather conditions at the target (dust or sand storms) causing issues with terminal laser guidance. Low cloud cover and haze can also prevent acquisition of target until it is too late for terminal corrections. In jungle fighting, the high jungle canopies and ambient moisture levels can blind the seeker to ground-based illuminators. Satellite guidance has the advantage over laser guidance in being impervious to weather and visibility conditions, but is vulnerable to jamming and cannot engage mobile targets. Precision guidance kits can be used to convert unguided rounds. These include course correction fuses which can correct for range and direction (2-D) or only for one of these parameters (1-D). Doing so reduces maximum range of converted ammunition, typically by less than 10%.
As noted above, laser guided munitions may be guided to target by an external operator. Aside from already noted limitations, this also places the operator in some danger, and is best used for supporting the troops already in combat contact with the enemy. When using laser-guided rounds against targets that are not within ground troops’ line of sight, drones and UAVs can be used for painting the target, as well as providing control of hit placement by live video feed (latter can be done regardless of the ammunition type). This also means that artillery shells can be used in urban environments, where unguided weapons (other than helicopter and CAS aircraft guns) are typically not used for fire support due to high margins of error, whereas aircraft-dropped guided munitions are simply too destructive. Laser-guided non-explosive shells might be especially useful for such purposes, but the high cost remains an issue. Precision munitions are also very useful for self-propelled artillery, which has low onboard ammunition capacity, as well as in conventional warfare for tasks such as eliminating ATGM nests, artillery positions, fortifications and similar point targets.
Precision of unguided rockets can be improved through usage of pulsejet control systems as well as active damping immediately after the rocket exits the launch tube; active damping can increase precision by a factor of 2,5. Due to relatively low speed, especially post-launch, long flight time, low density and large side area, rockets are particularly vulnerable to influence of disturbances on their hit precision. This means that they are primarily area bombardment systems, which requires large number of rockets from multi-tube launchers. Rocket artillery’s longer range, high fire power concentration in a short period of time, low launcher price and its high mobility mean that rockets are still useful in conventional warfare, but far less so in counterinsurgeny operations.
Ammunition accounts for a major portion of logistical needs of a modern motorized unit. During the Gulf War, Iraq’s ammunition expenditure surpassed 400 rounds per gun per day. In World War II, desired expenditure was 60 rounds per gun per day, but rationing due to insufficient logistical support limited US Third Army howitzers to only 1,1 rounds per gun per day between 15 and 21 October 1944.; other artillery pieces were similarly restricted. In the Vietnam War, average expenditure was 50 rounds per gun per day.
NATO countries use system of flat racks which allows quick and efficient transportation of ammunition. US approach is to have an armoured tracked vehicle for ammunition transport for each self-propelled gun. Self-propelled gun is suppled through the conveyor, thus leaving the onboard ammunition stores intact in the case of emergency. British approach is to provide each 155 mm battery with capacity for carrying containers, each containing 17 pieces of 155 mm ammunition. These are transported to guns by fork lift.
A special problem is interoperability between different NATO militaries. This does not only mean ability to fire ammunition utilized by another NATO military, but also avaliability of ballistical data and technical documentation for training purposes.
Precision munitions can help reduce logistical burden in terms of mass, which is to say rounds transported to the front and necessary logistical train, as less rounds will be required to complete any given objective (excepting those where volume is of importance). On the M795 projectile, the PGK was shown to decrease the amount of rounds that needed to be fired by 75% to 93%, which has substantial benefits in terms of reducing the logistics burden. However, they could make interoperability problems even worse, and may or may not reduce or increase price of any given fire mission. They are also not efficient for missions such as area suppression due to high price – 60.000 USD per projectile for Excalibur – and are thus only really suited for eliminating point targets. Smaller number of projectiles required to eliminate targets does have an advantage of reducing tube wear, and thus support requirements of the vehicle itself. Further, guided shells can in many cases replace guided missiles, thus reducing price per target destroyed as well as reducing logistics train due to their smaller size.
Despite all the claims to the contrary, direct and indirect fire artillery cannot be replaced. This has been confirmed by the Israeli Army in Operation Protective Edge. In Sheihaya, the IDF sent the Golani Brigade into the city in northern Gaza without “softening it up” in advance because it did not want to endanger civilians, who had been warned to leave the city. Several hours later, the army had lost 13 soldiers with dozens more wounded. The enemy, around 900 militants, was concealed in civilian structures and pouring down fire on the troops. The army brass, for the first time since the 1982 Lebanon War, ordered the soldiers into armored personnel carriers and, despite the lack of a sufficient safety range, fired 600 artillery rounds within half an hour. In the end, IDF may have fired up to 7.000 shells during the battle. As such, issue of artillery munitions will remain open.
Hrvatski Vojnik, Broj 7, godina VI, Siječanj 1996 (Croatian Soldier, No. 7, Year VI, January 1996)