Artillery ammunition is designed for use in guns, howitzers, and mortars. Size designations for artillery ammunition range from 37MM through 280MM. Artillery ammunition can be classified according to weapon system (gun, howitzer, mortar), filler composition (explosive or chemical), and military use (practice or service). The diameter, or interior, of a weapon barrel is designated by the term weapon bore. A weapon bore may be characterized as smooth or rifled. The barrel of a smooth weapon bore, as illustrated at bottom left, has a relatively flat, smooth surface. The size of the smooth bore weapon is simply its diameter (width of the barrel) .
Artillery ammunition is composed of the following five general components, each depicted in the fig Projectile, Cartridge case, Fuze, Propelling charge, and Primer. The projectile is the component that is propelled from the weapon towards the intended target. The cartridge case serves as the container for the propelling charge and houses the primer. Cartridge cases can be made of steel, brass, or a combustible material. The propelling charge propels the projectile from the weapon and is carefully designed for the particular role of the ammunition. The primer is the initiating component in an item that produces the flame to ignite the propellant. Primers used in artillery ammunition are classified according to their method of firing as either electric or percussion.
Anti-aircraft and other artillery rounds typically consist of an outer shell packed with a large amount of high explosives. These explosives are relatively stable and require the activation of a fuse to detonate. The fuze is the device used with a projectile to cause it to function. A fuze is a mechanical or electronic device used to initiate the explosive train. It can be found in everything from mortar and artillery rounds, to missiles and other projectiles.
The fuze determines when and under what conditions a projectile will function. A fuze activates the warhead mechanism in the vicinity of the target and also maintains the warhead in a safe condition during all prior phases of the logistic and operational chain. Fuze functions through explosive train which comprises of a detonator/ igniter that generates detonation wave which is further boosted up by a booster that in turn detonates the main explosive filling. Fuzes normally have two explosive components in their explosive train: a very small detonator (or primer) which is struck by a firing pin, and a booster charge at the base of the fuze (sometimes called the ‘magazine’).
In most cases, the fuze action causes detonation of the main high explosive charge in a shell or a small charge to eject a carrier shell’s contents. These contents may be lethal, such as the now-obsolete shrapnel shell or modern sub-munitions, or non-lethal such as canisters containing a smoke compound or a parachute flare.
The fuze action is initiated by impact, elapsed time after firing or proximity to a target. In a typical mechanical fuze, this is done by force of striker. In an electronic fuze, the initiation is done by an electric pulse generated by a firing circuit.
An ideal fuze would detonate the projectile at the most favourable position to inflict maximum damage to the target. The fuze-warhead process is singular and irreversible therefore requires high reliability. The quality required of fuze designs is usually specified by two values: functional re-liability, which ranges typically from 0.95 to 0.99 for complex missile fuzes, and to 0.999 for projectile and bomb contact fuzes; and safety reliability, for which a failure rate not greater than 1 in 106 must be proved prior to release of items for service usage.
Traditionally, the fuze provides safety by keeping one part of the explosive train in misaligned condition and align the explosive train after launch of the projectile and then detonates the explosive when specified conditions (like time/space) are sensed. To keep the fuze and ammunition safe, suitable safety interlocks like ‘g’ sensors, electronic or mechanical timer, pyro delay elements, etc. are used. The explosive train is aligned at appropriate instance during the flight. Fuze is initiated by initiation of first element of explosive train after sensing some input.
Being sensor devices by nature, fuzes are subject to a wide spectrum of disturbing influences in the real-world tactical environment. One of the foremost prerequisites of good fuze design, therefore, is to devise a sensor system that discriminates bona fide target return from all distracting influences, whether they take the form of electronic or optical countermeasures, intense electromagnetic radiation levels characteristic of fleet environments, chaff, precipitation, out-of-range targets, or radar clutter such as occurs in missile flight at low altitude.
The fuze technologies are being enhanced in many ways, through improved operational flexibility capable of supporting multi missions, setting of all fuze parameters through data links, terminal effect enhancement and improved safety and reliability.
Fuze System Classification
There are four major types of artillery fuzes: impact (percussion) fuzes, airburst fuzes, multifunction fuzes and sensor & course correcting fuzes.
A. Impact Fuzes
They are the type of fuzes which detonate the explosive charge when the munition hit the target. The detonation action could be happened directly by hitting the target or delayed after hitting the target. There are two major types of impact fuzes, direct action fuzes and delay fuzes.
1) Direct action fuzes
Direct action fuze starts its function when the fuze nose hits something reasonably solid, such as the ground. This action pushes a firing pin into a detonator which detonates a booster charge that is strong enough to detonate the explosive charge.
2) Delay fuzes
Direct action fuzes can have a delay function, selected at the gun as an alternative to direct action. Delay function may be achieved using different delay mechanisms. One of these mechanisms is the deceleration resulted from hitting a ground.
B. Airburst Fuzes
Unlike impact fuzes, airburst fuzes are the type of fuzes which detonates the explosive charge at a distance from the target. They are particularly important and were widely used. There are four major types of airburst fuzes; time fuzes, proximity fuzes, distance measuring fuzes and electronic time fuzes.
1) Time fuzes
Artillery time fuzes detonate after a predetermined period of time. Early fuzes were igniferous or combustible using a powder train.
The time length of a time fuze is usually calculated as part of the technical fire control calculations. The problem with these fuzes was that they were not very precise and somewhat erratic, but good enough for flat trajectory fragments or high bursting carrier shells.
2) Proximity fuzes
The benefits of a proximity fuze that functioning when it detects a target in proximity are obvious, particularly for use against aircraft. Proximity fuzes are the most common fuzes used in artillery projectiles because they can measure the range accurately especially after the recent developments achieved in them.
3) Distance measuring fuzes
The distance measuring fuzes or mechanical distance fuzes have been used a little. It has the advantage of inherent safety and not requiring any internal driving forces but dependeds only on muzzle velocity and rifling pitch.
4) Electronic time fuzes
In the late 1970s / early 1980s, electronic time fuzes started replacing earlier types. They were based on the use of oscillating crystals that had been adopted for digital watches. Like watches, advances in electronics made them much cheaper to be produced than mechanical devices.
C. Multifunction Fuzes
A multifunction fuze assembly may include more than one fuze function. A typical combination would be a T & P (“Time & Percussion”) fuze with the fuze set to detonate on impact or expiration of a preset time. Initially, they were little more than enhanced versions of proximity fuzes, typically offering a choice proximity heights or impact options. They were much more widely issued. In some countries, all their war stock of high explosives (HE) were fitted with them, instead of only 5 to 10% with proximity fuzes.
D. Sensor and Course Correcting Fuzes
Sensor fuzes can be considered smart proximity fuzes. Initial developments were the United States ‘Seek and Destroy Armour’ (SADARM) in the 1980s. These sensor fuzes typically use millimetric wave radar to recognize a tank. The main fuze development activities in the early 21st
century are course correcting fuzes. These fuzes add guidance and control functions to the standard multi-option nose fuze package.
Proximity fuzes accomplish their purpose through “influence sensing,” with no contact between the warhead and target. These fuzes are actuated by some characteristic feature of the target rather than physical contact with it. Initiation can be caused by a reflected radio signal, an induced magnetic field, a pressure measurement, an acoustical impulse, or an infrared signal. Proximity fuzes are the most common fuzes used in artillery munitions. This is because of their advantage of inflicting maximum damage of the target they deal with. A proximity fuze is classified by its mode of operation, of which there are three: active, semi-active, and passive.
It is reported that one humble piece of equipment that got an early upgrade that may have actually tipped the war in America’s favor was the proximity fuse. Till then, timed fuses were being used which were less than perfect, and small math errors could lead to a round going off too early, allowing the shrapnel to disperse and slow before reaching personnel and planes, or too late, allowing the round to get stuck deep into the dirt before going off — the dirt then absorbs the round’s energy and stops much of the shrapnel.
Top-tier talent, like Dr. James Van Allen, the one the “Van Allen radiation belt” is named after, managed to create a working fuse that detonated near its target approximately half the time. So, to suddenly have rounds that would explode near their target half the time, potentially bringing down an enemy plane in just a few dozen or few hundred shots, was a revelation. This solved a few problems. Ships were now less likely to run out of anti-aircraft ammunition while on long cruises and could suddenly defend themselves much better from concerted bomber attacks.
Development of Proximity Fuze Technology
In the last three decades, the proximity fuze technology has become more advanced and evolved considerably. The
advancements in proximity fuzes have taken place in the following areas:
Accurate height of burst in ground fuzes.
Optimum point of burst against airborne.
Resistant to severe electronic countermeasures.
Ultra wide band fuzes.
Advanced signal processing techniques.
Application of Monolithic Microwave Integrated Circuit (MMIC) techniques. MMIC are devices that operate at microwave frequencies, (300 MHz to 300 GHz), in the front-end/RF system in the fuzes.
Impact fuze detonates and losses more than 50% of its energy compared to the case if explosion takes place at certain high. Proximity fuze is used to enhance the performance of warhead explosion and increase the effective distance of fragmentation warhead. Optimum burst point varies according to the nature of the target and the properties of the shell itself.
For example, optimum burst point against an aerial target could be closest point of approach to the aircraft or an optimum point according to some preset criteria by the signal processing algorithm. Against ground, the optimum burst height varies from 2 m to 20 m for fragmentation and blast bombs, 100 m for a chemical warfare bomb, 3 m for 81 mm mortar and 12 m for a 155 mm field artillery shell.
A. Classifications of Proximity Fuzes
Proximity fuzes can be classified according to ammunition, targets, fuzing techniques and antenna configuration.
According to fuzing techniques
a) Pulsed Doppler
Pulsed Doppler fuzes have limited application which require functioning at high altitude between 1000 to 5000 ft, it is required also in dispensing submunitions.
b) Continous Wave (CW) fuze
CW fuzes primarily measure the target echo Doppler shift. Range cannot be measured directly (there is no time reference) but it is measured indirectly from the strength of received signal. Proximity fuzes of the World War II and till early 1980’s, used CW fuzes. This type of fuzes has the disadvantages that it can be easily jammed and the range measurement is not accurate.
c) Frequency Modulated Contious Wave (FMCW) fuze
FMCW fuzes using sinusoidal and linear triangular modulation have the capability of measuring target range. Fuzes of most ammunition use the linear FMCW technique owing to their excellent features. Wide band FM modulations achieve very high target range accuracies. The FMCW systems are also resistant to ECM. Their deterministic waveforms also allow the signal processing using Fast Fourier Transform (FFT) techniques.
d) Pseudo-random binary-coded and noise-modulated
The pseudo-random binary-coded and noise modulated fuzes use time-variant modulations on the CW and are capable of measuring the target range. These waveforms are more complex than the FMCW waveforms and need correlators in the signal processors to extract range information. They cannot be jammed easily because of the complexity of their waveforms.
e) Pulsed laser fuzes
The pulsed laser fuzes is characterized by having very high precision in ranging and very high resistance to countermeasures. On the other hand, the laser source used in artillery projectiles is very expensive
Electromagnetic Proximity Fuzing
An electromagnetic fuze, operating particularly in the radio and radar region, may be constructed to operate much like a miniature radar set. It must transmit, receive, and identify electromagnetic pulses. The proper received signal initiates the detonator. The portions of the electromagnetic spectrum used for target detection having the greatest utility are radio, radar (microwaves), and infrared.
Surface Weapon Application. Some weapons used against surface targets, such as bomblets delivered to the target area in canisters called cluster bomb units (CBU) and fuel-air-explosive (FAE) weapons, employ proximity fuzes to deploy and disperse the payload at a predetermined height.
Anti-personnel weapons having unitary warheads are more effective when detonated above the target area than on contact. Proximity fuzes for these applications may function as radio or electro-optical altimeters or as slant-range-sensing devices that measure range to the surface at the projected point of weapon impact.
One means of signal selection makes use of the radar principle, in which the elapsed time between a transmitted and received pulse is a function of range between target and weapon. Another means makes use of the doppler principle, in which the frequency of the received signal varies as a function of the relative velocity between the weapon and target. This permits the classification of targets according to their radical velocities, which is useful in the selection of a primary target within a group of signals from a variety of sources. The doppler frequency can also be used to determine when to detonate the warhead.
Missile Fuze Applications. In air-target weapon applications, the main function of the proximity fuze is to compensate for terminal errors in weapon trajectory by detonating the warhead at a point calculated to inflict a maximum level of damage on the target. The system engineer strives for a fuze design that will adaptively initiate the warhead within the so-called “lethal burst interval” for each trajectory that his weapon is likely to experience in future oper-ational usage. The lethal burst interval is defined as that inter-val along the trajectory in which the warhead can be denoted so as to hit the target in the vulnerable area.
Magnetostatic Fuze Applications.
Magnetic sensors, such as magnetic anomaly detection (MAD), measure changes in the earth’s magnetic field or the presence of a source of magnetic flux. In the case of fuze systems,a magnetic sensor is designed to recognize an anomaly and ultimately cause the fuze and safety and arming (S&A) device to function. Magnetostatic fuzing is also used for subsurface targets. The magnetic field disturbance fuze for subsurface targets is also actuated by a change in the surrounding magnetic field. Any change in the magnitude of the magnetic field activates the fuze.
Acoustic Fuze Applications.
Acoustic disturbances, such as propeller and machinery noises or hull vibrations, invariably accompany the passage of a ship through the water. The intensity or strength of the sound wave generated depends upon several factors, such as ship size, shape, and type; number of propellers; type of machinery, etc. Therefore, a ship’s acoustic signal is variable, and acoustic fuzes must be designed to prevent an intense signal from actuating the fuze at distances well beyond the effective explosive radius of the payload.Acoustic fuze mechanisms are used in torpedoes as well as mines.
A similar type of acoustic influence sensor used in some types of mines is the “seismic” firing mechanism. This sensor is essentially an acoustic fuze, but receives its threshold signal in a lower bandwidth through weapon-case vibration. These sensors can be made extremely sensitive and may provide for both land-based or in-water application.
Hydrostatic (pressure) Fuzing
Oceans swells and surface waves produce pressure variations of considerable magnitude. Moving ships displace water at a finite rate.This pressure variation, called the “pressure signature” of a ship, is a function of ship speed and displacement and the water depth. Various pressure-measuring mechanisms can be used in fuzes to detect such variations.
Pressure sensors are commonly associated with bottom mines and are extremely difficult to counter through normal influence-mine countermeasure techniques. Pressure-firing mechanisms are seldom used alone,but are generally combined with other influence firing devices.
Systems involving a combination of influences are available in most mine firing devices. The combinations of magnetic, pressure, and acoustic/seismic systems are used to compensate for the disadvantages of one system with the advantages of another. Mine counter-measure effectiveness can be greatly reduced through use of combination fuzing.
BAE has developed 6-mode programmable 40 and 57 mm Bofors 3P (Pre-fragmented, Programmable, Proximity- fused) ammunition can be programmed in six different function modes to provide optimised effect against any aerial, surface or shore target. This provides weapon systems with the highest possible combat flexibility.
Each 3P fuse is automatically and individually programmed by a Proximity Fuse Programmer which continuously receives data from the Fire Control Computer System. Immediately before firing, the fuse is programmed to the selected mode. It gives forces superior handling of traditional threats such as anti-ship missiles, aircraft, ships and shore targets, including those with armour protection. It also provides completely new capabilities. Functions such as airburst deal with threats that previously were impossible to engage, such as small, fast-manoeuvring boats and concealed targets.
Kaman wins direct commercial sale order for joint programmable fuses in 2018
Kaman’s aerospace segment has secured a direct commercial sale order for the procurement of new joint programmable fuses (JPF). The JPF is an advanced fuse used with precision weapons systems such as the joint direct attack munition (JDAM). The fuse is fitted with variable delay capabilities that allow the settings of a weapon to be programmed manually or from the cockpit through its in-flight re-programmability feature.
The bomb is claimed to be the USAF’s current bomb fuse of choice, and is used with an array of weapons, such as general purpose bombs and guided bombs that use joint-direct attack munitions, and paveway kits on a range of US and international aircraft. The aircraft that use the fuse include the US’ F-15 Silent Eagle, F-16 Fighting Falcon, F-22 Raptor, A-10 Thunderbolt, B-1 Lancer, B-2 Spirit, B-52 Stratofortress, the MQ-9 Reaper unmanned aerial vehicle, as well as the international fighter jets such as the Mirage 3 and JAS 39 Gripen.
Since 2002, Kaman has been providing the JPF to the USAF and 26 other countries worldwide.
Dezamet supports novel fuze of F-35’s APEX ammunition
Nammo’s 25mmx137 APEX (armour-piercing with explosive) ammunition has been qualified for the F-35 Lightening II advanced stealth fighter following flight trials at the US Navy’s Naval Air Weapons Station in China Lake, California. Designed specifically for the F-35, the APEX is intended to defeat a spectrum of target types – ranging from air targets to both so and armoured ground targets. All this – using munitions with a projectile of a diameter of 25 mm. This meant a necessity of combining the properties of HEI class ammunition (high explosive incendiary) and API class ammunition (armour piercing incendiary) in one projectile.
The ammunition features an explosive filled warhead with a delayed initiation – meaning that the blast, fragments and incendiary are delivered inside the target and a tungsten carbide penetrator to defeat heavier armoured targets. The hit mechanism of the projectile body is divided into separate phases depending on the type of target engaged. The mechanical fuze will support the transition between the phases of target defeat. For targets with light to medium protection, the projectile body can make full penetration with a time-delayed fuze to ensure maximal blast and fragmentation well inside the target.
Nammo had signed a contract for specific work with DEZAMET – for development and implementation of this fuze into production. The requirements for a fuze for APEX were very high. Norwegians expected development of a mechanical fuze, without any electronic components due to requirement of stable fuze parameters in extremely low temperatures, present in stratospheric flight ceilings of F-35.
The fuze would have to cause projectile detonation with the so-called constant delay, after hitting a non-armoured target, irrespective of the thickness of the skin that it encounters.The fuze had had to be significantly miniaturised. At the same time, it had to be resistant for various stress factors that take place during the flight as well as during shooting of the Gatling system gun. The muzzle velocity of the APEX 25 x 137 mm PGU-47/U projectile, for the GAU-22/A gun is about 970 m/s
Forces with complicated and variable vectors affected various elements of the small fuze, the design of which had to be included in a 25 mm projectile body. In such conditions the fuze mechanism had not only to remain capable of initiating detonation, but earlier – release and arm the fuze. In relation to the speed of processes connected with movement in the space, fractions of a microsecond had to be taken into consideration, during which specific sequences of mechanism’s operations had to be performed.
U.S. develops “super-fuze” under its Nuclear Force modernization
Under its Nuclear modernization program US has developed a “super-fuze” device that by making small adjustment to the height of warhead explosion results in revolutionary increase in lethality of U.S. submarine–launched ballistic missiles, according to the report in the 1 March issue of the Bulletin of the Atomic Scientists (BAS). The targeting change is part of the nuclear stockpile stewardship plan that began a decade ago and is aimed at maintaining the U.S. nuclear deterrent without the need to develop and test new weapons.
“Shortly before a warhead arrives at its target, the superfuze uses radar to gauge the distance remaining on the ballistic path, taking into account any drift off track. The old technology set the detonation at a fixed height at or near the ground; course errors could shift the center of the blast away from the target (see diagram). But the new system adjusts the detonation altitude so that the blast is triggered at a higher point to keep it in the target’s so-called “lethal volume.” Within this zone, the authors say, a 100-kiloton warhead will destroy a hardened structure with 86% certainty”. The public has “completely missed [the superfuze’s] revolutionary impact on military capabilities,” reports Eliot Marshall, a science journalist in Washington, D.C.
The BAS authors calculate that by the end of 2016, U.S. weapon facilities had already produced roughly 1200 of a planned 1600 W76s armed with the superfuze. Of these, they say, “about 506” are now deployed on ballistic missile submarines. They estimate that potentially 272 such warheads, with two sent against each target, could eliminate “all 136 Russian silo-based ICBMs [intercontinental ballistic missiles].” US submarine-based missiles can carry multiple warheads, so hundreds of others, now in storage, could be added to the submarine-based missile force, making it all the more lethal.
The increased capability of the US submarine force will likely be seen as even more threatening because Russia does not have a functioning space-based infrared early warning system but relies primarily on ground-based early warning radars to detect a US missile attack, writes Hans M. Kristensen director of the Nuclear Information Project with the Federation of American Scientists (FAS) in Washington, DC. Since these radars cannot see over the horizon, Russia has less than half as much early-warning time as the United States. (The United States has about 30 minutes, Russia 15 minutes or less.)
Trajectory correction fuze
Trajectory correction fuze is opening a low cost and high profit way to improve attack accuracy for various projectiles. By installing a fuze, projectiles can obtain the correction function without adding any sensors or changing the size. Without any modification of the projectile body, the conventional stock ammunition could obtain the capacity of trajectory correction by simply replacing the trajectory correction fuzes. As such, a fuze can improve the operational effectiveness and maximize the use of stockpiles, and it has received much attention.
The correction strategy design is the foundation for trajectory correction fuze. No matter what correction strategy is adapted, the relevant sensors’ feedback would be necessary. Generally, the GPS receiver is a common way to obtain the projectile position, while gyroscopes and accelerometers may be used to measure the projectile attitude. For a projectile with precise fixed-point initiation, a depth sensor is required. If a classic proportional navigation guidance is considered, a goniometer is needed to track the line of sight (LOS) . Additionally, a suitable filtering algorithm may be helpful in information processing during the positioning and tracking.
The control actuator is another indispensable part of trajectory correction. The common actuators for trajectory correction fuzes are nose-mounted canards and jet thrusters. Compared with the jet thrusters, the canard actuator has a lower cost and needs less modifications for original projectiles. Moreover, because of the restriction of propellant, jet thrusters are difficult to integrate into the fuze. Therefore, the canard actuator is more suitable for trajectory correction fuze. To complete both the crossrange and downrange correction, two pairs of canards are always involved in a general canard actuator
Recent years the artillery have been seeking a higher striking accuracy when using mortars to attack the target, to shorten operational time and reduce the operational loss. However, the accuracy improvement for current trajectory correction fuze has a limit because real-time information of the target is not involved in the mentioned strategies. The objective of this paper is to further improve operational effectiveness. Therefore, an image sensor was considered in the design of the trajectory correction fuze as it can provide the real position information of the target.
However, with increasingly complex operational backgrounds and missions, the guidance mode of trajectory correction fuze faces greater challenges. In this case, the infrared image sensor is widely used because of its long detection distance, good anti-interference ability and strong concealment. Therefore, the installation of a fuze with an infrared image sensor can not only improve attack accuracy, but also meet different mission requirements, which has received much attention.
Generally speaking, the space available and updated cost are limited for trajectory correction fuzes used for mortars, so there are some constraints on the inner components of the fuze such as sensors and actuators. Once the imager is used in trajectory correction fuze, the front-end space would be occupied, which would bring about more space resource constraints. Therefore, the balance between performance and affordability of the fuze should be achieved.
Li proposed a novel trajectory correction fuze based on an image sensor. Then, the correction strategy of mortars was studied to improve the attack accuracy. However, the previous research was based on the macroscopic trajectory and ignores the effect of projectile’s jitter on the image.
Compared with missiles, the infrared image sensor is rarely used in mortars. Since mortars are often launched from a smooth bore gun, they have a certain amount of micro-spin to keep balance. This causes a rotation of the field on the infrared image sensor. In addition, due to the influence of aerodynamic force, mortar will produce high frequency jitter. The above reasons cause the instability of the image, resulting in fuze not being able to accurately detect the target. Therefore, keeping a stable field is the precondition of improving the attack accuracy.
Generally speaking, video stabilization technology has been widely used in military and civilian fields, such as investigation, fire control, surveillance, in-vehicle and handheld cameras. It can be roughly classified into three categories, namely mechanical image stabilization (MIS), optical image stabilization (OIS) and electronic image stabilization (EIS). Compared with MIS and EIS, the components of OIS are complex and expensive. Additionally, the mortar has a high overload during launch, which will destroy the optical structure and make OIS impossible. Some MIS methods use gyro-scope for motion estimation, but that can only capture the rotational motion, leaving the translational motion undetected. The above problems lead to a lesser application of video stabilization technology on fuze. In addition, the fuze’s information is updated quickly due to the short trajectory distance and high-speed flight, resulting in a once stable cycle time that is much less than that of other types of carriers.
Generally speaking, the EIS can be equivalent to video stabilization and belongs to the category of image processing. According to the motion model of the projectile, video stabilization can be divided into 3D and 2D approaches.