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More bang for your buck--warhead technology.

As with any weapon system, the end result of an artillery fire mission has to be measured in terms of on-target effectiveness. As an analogy of current projectile design trends, today's automobiles cram at lot more power into their engine compartments than was possible as recently as a decade ago. Yet the engines remain as compact as before (if anything they grow smaller). The same thing is happening with artillery projectiles. Not only are they now capable of delivering more effective payloads, they also deliver novel types of content that extend the military applications of the artillery projectile to new possibilities.

Extended range is one of those possibilities. Now, as always, gunners regard maximum potential range as one of their main combat assets but at the same time demanding that their efforts to reach that range remain as productive as can be achieved--there is no benefit in delivering a minute warhead to 50 km. It is on this aspect of projectile delivery that this outline will concentrate. After all, it bears repetition that in weapon system terminology the projectile is the gunner's weapon. The noisy and imposing guns and howitzers are merely the delivery systems.

It is also worth repeating that traditional artillery is an area weapon and is not intended to be deployed against point targets (other than at extremely close line-of-sight ranges and "smart" and guided warheads). It therefore follows that once on the target area, the greater the number of fragments filling the inside of a high explosive projectile casing can create, the more effective a projectile will be.

As an example of what the latest projectile technology can achieve, it is necessary to consider what is still the most widely employed and manufactured of all current 155 mm artillery projectiles, the Nato standard HE M107, which can trace its design origins back to the 1914-1918 Great War era. Despite having shortcomings that will be outlined, and leaving range potential aside, it still remains in service for both training and combat applications around the world, remaining the benchmark by which all other high explosive projectile performances are measured. But by today's standards the HE M107 is well outmoded for several reasons. One is that its payload to weight ratio is too low. For a shell weighing anything between 41 and 43 kg, only just over 6.6 kg is explosive, either cast TNT or Composition B. In addition, the steel employed for the body has erratic and unpredictable fragmentation properties. Bearing in mind that the gunner's intention is to cover as wide a target area with effective fragments, when the payload detonates the HE M107 body produces an unpredictable number and spread of fragments that may vary in size from large chunks to useless dust.

By comparison, the HE projectile intended to replace the HE M107, with the US Army at least, is the HE M795, which has a much better all-round performance. The M795 body is longer than that of the M107 and can thus contain a larger TNT explosive payload compared to overall projectile weight. While a complete M795 weighs about 46 kg, no less than 10.8 kg is the cast TNT filling. However, the explosive payload is not the only factor that renders the HE M795 more effective than the HE M107.

The HE M795 body is manufactured using a higher grade of forged, hard, high fragmentation steel, usually a type known as AISI 9260 or a steel close to that standard. Introducing this steel results in a thinner projectile body wall than that for the HE M107, one offshoot being that the internal volume can be magnified still further. This type of steel is guaranteed to break up into a large number of small but effective fragments that will travel a more predictable distance from the point of detonation.

These high fragmentation steel bodies can have their performances enhanced by a technique usually associated with air defence gun projectiles. One current example can be seen with one of the projectiles designed for the South African Denel 105 mm Light Experimental Ordnance (Leo). One of the Leo HE projectiles is the XM9759A1 HE PFF. The PFF stands for Pre-Formed Fragmentation. In addition to the enhanced effects produced by the high fragmentation steel body, the shell's inner walls are lined with a layer of small steel spheres that add to the on-target mayhem created on detonation. When used with a Fuchs Electronics proximity fuze set to function at a pre-selected height above the target surface, the resulting combination of body fragments and steel spheres can cover a lethal area of about 2000 metres. This can be compared to Somchem's 155mm ERFB (Extended Range Full Bore) projectile with an RDX/TNT filling that covers a similar lethal area. For further comparison, a standard 155 mm HE M107 projectile filled with TNT has a lethal area measuring about 1000 metres.

The PFF technique has yet to be applied to operational 155 mm projectiles, but its introduction should not be long in coming. After all, the Leo projectiles are only scaled down versions of the Naschem Assegai ERFB 155 mm enhanced range projectiles, so the introduction of PFF to the 155 mm family should be feasible with little difficulty.

Thermobarics

Although not yet employed with artillery, the thermobaric warhead for artillery applications is almost certainly on its way. Currently deployed mainly with relatively low-velocity delivery systems, such as guided missiles, thermobaric warheads can create fearful on-target effects in the form of extremely high temperatures and blast pressures. To date they have been confined to low velocity applications by the need for a short-lived but significant time interval to allow the warhead contents to form an aerosol cloud prior to detonation.

Thermobaric warheads were developed from experience gained with the so-called fuel-air explosives. These relied on creating a concentrated aerosol cloud formed from a highly volatile liquid or powder explosive mixture (or a mixture of both). The cloud is created on impact or via a time fuze by a small explosive charge just prior to being detonated by a second, larger charge. Each aerosol particle is then able to burn extremely rapidly, the combined results being a very rapid rise in temperature and a high velocity blast wave.

Thermobarics involve advanced and refined fuel-air techniques, including the introduction of insensitive polymer-bonded explosives in a fine powder state to form the aerosol cloud. One such explosive known to have been involved in US Navy experiments is known as PBXIH-135, although whatever explosive is employed it no doubt contains traces of magnesium and aluminium oxides to assist combustion. The explosive aerosol burns extremely rapidly to create temperatures of the order of 3000[degrees]C, consuming all available oxygen from the air through which it passes (it is for this reason that the Russians recommend thermobaric devices for extinguishing fires.) The rapid increase in temperature results in an intense over-pressure blast wave that travels outwards at a velocity of over 3000 m/s.

As already mentioned, thermobarics have been adopted as alternative warheads for anti-tank guided missiles, nearly all such applications originating within Russia with systems such as the Kornet and the Metis. They have even been introduced to weapon calibres as small as the 43 mm GM-94 magazine grenade launcher, which is intended primarily for urban warfare. One of the best-documented thermobaric warheads is the one employed with the RPO-A Schmel (Bumblebee), described as a shoulder-launched flamethrower for infantry. The warhead is launched within what the Russians describe as a capsule, a blunt nosed, thin-walled container that detonates on impact. The capsule warhead has a calibre of 93 mm yet it is claimed to produce severe effects on structural targets equivalent to those for a 122 mm HE artillery warhead.

The Schmel entered full production in 2001 although pre-production examples were previously deployed in Chechnya, being responsible for much of the structural destruction wreaked throughout Grozny. So destructive was the Schmel that many overseas observers took note, the result being that several other nations are actively developing their own equivalents. Thermobaric warheads for laser-guided aircraft bombs have already been deployed operationally in Afghanistan, where they proved to be dreadfully effective against targets within caves.

Artillery projectiles with thermobaric warheads may still be some way off but the infantry soldiers that the gunners usually support already have their own short-range delivery systems in the form of the formidable Schmel. Once the time period required to form the aerosol clouds essential to thermobaric warhead performance has been reduced by technical development artillery applications will follow.

A number of missile and rocket warhead manufacturers, like Ruag, are investigating the potential of thermobaric warheads. Indeed, as the trend for urban warfare increases, small thermobaric warheads appear as an attractive solution to 'treat' a building or a bunker.

Heat and Hesh

In contrast to the warheads mentioned above, Heat (High Explosive Anti-Tank, the well-established shaped charge) and Hesh (High Explosive Squash Head, also known as Hep, or High Explosive Plastic) are currently not in favour. Both are primarily intended for use against armour but with tank guns Heat projectiles are too inaccurate at the longer ranges, being too slow in flight to overcome environmental factors such as side winds. Many nations have never regarded the versatile Hesh as worthy of adoption, but that is beginning to change.

One reason is that recent experience has demonstrated that armoured vehicles can be expected to be deployed in built-up urban areas to a greater extent that was once foreseen, and that includes self-propelled artillery as well as tanks (as in Iraq). During Fighting In Built Up Areas (Fibua), armoured vehicles have to operate with close infantry support to keep enemy tank-killer squads at bay. In their turn, the infantry must be provided with fire support such as demolishing strong points or smashing holes through walls or doors to allow the infantry to pass through. While simple high explosive projectiles might suffice for such tasks, the anti-armour capabilities of Heat and Hesh add to mission flexibility. It is for this reason that large calibre Heat and Hesh projectiles are once again under examination for the artillery.

Recent developments relating to Heat charges have resulted in some novel shapes for the shaped-charge warhead cavities. While a simple, straight cone contour might be effective enough for most purposes, recent innovations have resulted in a cavity resembling a trumpet bell that concentrates the armour penetrating high temperature jet considerably. This feature enables a projectile such as the Bofors 106 mm 106 3A-Heat-T fired from 106 mm M40 series recoilless rifles to penetrate over 700 mm of armour, further protected with add-on explosive reaction armour modules.

As explained to Armada by a Ruag specialist, there is still quite a lot of room for improvement in warhead technology, but oddly enough, more in shaping and manufacturing processes than in chemical contents. For instance, the Swiss firm is actively developing shrink-fit techniques, which not only enable the explosives to be more coherent and crack-free, but also allows them to snugly fit their respective shell or liner cavities.

Cargo

Cargo projectiles are now so commonplace that it is often forgotten that they have been around for only a couple of decades. The introduction of the 155 mm Improved Conventional Munition (ICM) M483A1 arrived in time for it to see operational use as recently as the first Gulf War of 1990-1991 but since then has proliferated considerably, and many other comparable cargo projectiles have appeared, including mortar cargo bombs.

By scattering dual-purpose anti-armour/anti-personnel sub-munitions (also known as bomblets) over a wide area (up to as much as six times greater than possible with conventional HE projectiles) the cargo projectile considerably expands the utility of artillery as an area target weapon. The small submunitions usually employed may have only a limited armour penetration performance but it is enough to cause damage to lightly armoured vehicles and inflict secondary damage to heavier vehicles such as tanks.

Submunition development continues, mainly to correct an unfortunate shortcoming of the first generation of M42/ M46 pattern rounds. These submunitions rely on mechanical action impact fuzes, which, for various reasons, do not always function as intended. One generally accepted figure is that about 15 per cent of any M483A1 projectile's payload will not detonate on impact, the duds remaining around to present a serious hazard to all who approach; enemy or friendly, soldier or civilian. Clearing up the aftermath of a cargo projectile fire mission thus became a serious (and dangerous) chore, therefore, the latest generation of submunitions feature integrated self-destruct mechanisms.

Typical of these is the Israel Military Industries' (IMI) M85, which will self-destruct about 15 seconds after impact should the impact fuze fail to function. The M85 is utilised with several IMI cargo projectile products, one being the 155 mm CL 3013-U-A2 procured by the British Army to extend the effectiveness of the AS90 self-propelled field batteries. The British Army designation is Extended Range Bomblet Shell (ERBS) L20A1. Rheinmetall DeTec has made an agreement to promote the use of IMI submunitions, including integrating them with its own products. The company has already produced its 155 mm DM 662 cargo projectile carrying 49 M85 bomblets for Norway. Switzerland purchased projectiles direct from IMI, again containing M85 submunitions with their all-important self-destruct feature. With these Rheinmetall and IMI cargo projectiles, most of the dispensed submunitions will fall into a circle with a diameter of 100 to 120 metres.

To extend the self-destruct feature still further, the Spanish Instalaza Mat-120 cargo projectile for 120 mm mortars has an impact fuze backed up by an electronic self-destruct mechanism. Instalaza even pushed the art to the extent that should the self-destruction device fail to operate, the submunition becomes totally inert thanks to a fail-safe system. In addition, Instalaza's fuze design is such that all can be tested prior to final assembly. Electrical power for the submunition and bomb time fuze operations is created by a small air-driven turbine in the fuze nose so there is no form of stored energy when the bomb is stored or transported. The Mat-120 carries 21 submunitions, each large enough to defeat 150 mm of armour while spreading 650 anti-personnel fragments. It seems almost certain that electronics will intrude into the world of artillery projectiles a great deal in the years to come.

In their usual fashion, the Russians have adopted the cargo projectile and submunition but have chosen to dispense far larger submunitions. Their 152 mm 3013 projectile carries just eight submunitions, each weighing 1.4 kg (an IMI M85 submunition weighs 44 grams). The area coverage may not be as great as with the small DP submunitions but any impact with an armoured target will almost certainly inflict serious harm.

Cargo projectiles can carry payloads other than explosive submunitions. Another Russian 152 mm cargo projectile, the 3RB30, contains a single body containing a radio jammer, the intention being to fire the cargo projectile to a pre-selected target area and then eject the jammer to fall, under parachute control, to the ground. Once there, the jammer will start broadcasting to disrupt radio communications over a radius of up to 700 metres for about one hour, and then cease operating.

Some may object that anti-armour warheads have not been covered in this article. This is because they were extensively described in a recent issue of Armada (see 6/2002).
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Title Annotation:Technology
Author:Gander, Terry J
Publication:Armada International
Date:Aug 1, 2003
Words:2559
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