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Further to the point: until recently, the artillery world was divided into two camps -- those who had embraced Extended Range Full Bore (ERFB) technology and those who had not.

Further to the point: until recently, the artillery world was divided into two camps -- those who had embraced Extended Range Full Bore (ERFB) technology and those who had not. ERFB adherents enjoyed the artillery benefits of ranges once regarded as in the science fiction bracket, while the more conventional gunners pointed to ERFB manufacturing and handling difficulties and to the long and heavy barrels (and carriages) that had to be used to gain maximum advantage from the ERFB. (Technology)

The debate continues, even though it has become apparent that the differences between the two camps have all but vanished. One of the main reasons is that ERFB technology has been advanced to the point where what may be regarded as the original variations from conventional projectile design (the long conical streamlined outline, the necessary and expensive bore-riding nubs and drive band niceties) have now been all but eliminated. The latest generation of projectiles has all the long-range advantages of the early ERFBs but now combined within a seemingly conventional but still carefully profiled and streamlined package.

Most of the old carpings relating to ERFB (Extended Range Full Bore) have also all but vanished. Artillery fire control system capabilities can take full advantage of the 50,000-metre plus ranges now possible. Target acquisition at such ranges, once a major argument against the immediate procurement of ERFB, can be overcome by the employment of suitable remotely controlled aerial platforms or even space satellite observation. Such measures may be taxing in terms of cost, resources and skilled personnel, but to the gunner the expense is worth such investments. Apart from the fact that battlefield survivability chances are enhanced and fewer gunners are needed, a single ERFB-equipped battery can deliver payloads to a much larger swathe of terrain than is possible with more conventional batteries, and with better long range accuracy than was once the case.

As for the criticisms regarding barrel length, 52-calibre barrels are now accepted as a norm.

Assegai

These recent changes can be readily appreciated by an examination of the Assegai family of 155 mm projectiles available from Naschem, part of Denel in South Africa. The South Africans have remained enthusiastic proponents of ERFB from the time during the late 1970s when the concept was developed under the aegis of the late Dr Gerald Bull and his Space Research Corporation team, and have since remained at the forefront of all recent ballistic developments.

Naschem has developed its 155 mm Assegai family to the point where not only is it optimised for the latest 52-calibre barrels but also compatible with 47-, 45- and 39-calibre barrels. This is a considerable technical achievement brought about by, among other details, a carefully designed drive band configuration. In addition, the revised bourrelet outline (that is, the nose shape) renders it fully compatible with Nato standard requirements (the original ERFBs were not). Assegai projectile natures remain as varied as with the original ERFB generation, including cargo (containing 42 dual-purpose bomblets with self-destruct mechanisms), illuminating, smoke and incendiary payloads. All projectiles within the Assegai family are ballistically matched, including a practice projectile with a spotting charge.

Assegai ranges are considerable once base bleed (or base burn -- BB) units are added to the projectile bases. Existing BB units can be employed with Assegai projectiles so that ranges of more than 40,000 metres can be achieved from a 52-calibre barrel. Even without BB the maximum range is over 30,000 metres.

For HE (High explosive) rounds, the Assegai on-target effects are considerably amplified by the 8.3 kg TNT payload creating more lethal fragments than more conventional equivalents, thanks to the forged high grade steel employed for the shell casing.

V-Lap

At one time the most widely applied method of extending the ballistic trajectories of artillery projectiles was adding a rocket motor to be ignited at the point during the trajectory where the initial barrel-induced momentum starts to fade away. This technique, Rocket-Assisted Propulsion or Rap, has been widely adopted, especially in the USA where it was for long preferred as a range extension technique, even after BB became available. The application of BB results in far better long range accuracy than when using Rap as there are too many variables regarding rocket ignition and burn times, even after following carefully-controlled manufacturing and handling procedures. As BB merely disrupts tail drag eddies and does not impart any propulsion, its effects can remain fairly constant compared to those for Rap.

However, Rap can still impart extra range and has thus been adopted, by Somchem in association with Naschem, for the Velocity-enhanced Long Range Projectiles (V-Lap), but in association with BB. First applied to the original `nubbed' Naschem/Somchem HE ERFB projectile, the V-Lap approach has now been adapted for the Assegai M2005 HE projectile. After firing, the BB unit ignites as before and is completely consumed before the Rap motor is ignited. The resultant thrust then provided enables ranges of over 53,000 metres to be reached when 52-calibre barrels are involved. There are few gunners who would consider firing V-Lap from anything less than the optimum 52-calibre barrels, although even when fired from a 39-calibre barrel Assegai M2005 HE V-Lap range is still over 41,000 metres.

Needless to say, this performance enhancement has to be paid for. The Rap and BB units occupy space inside the V-Lap projectile so the payload has to be reduced to 4.5 kg of TNT. It is doubtful if a recipient would appreciate the difference in the resultant detonation, especially if the V-Lap projectile is delivered to a target previously thought of as safely within a rear area.

Naschem and Somchem have yet to finish with the V-Lap concept. It is understood that they are currently investigating the installation of a nose-located ramjet motor that will start to produce thrust only when the projectile's maximum velocity has been achieved soon after firing. No range figures have yet been announced but they will no doubt display a considerable improvement compared to current achievements.

Leo

Before leaving the South African scene, mention must be made of the recently announced Denel 105 mm Light Experimental Ordnance, or Leo. Leo is an interesting development for, until only a few years ago, the 105 mm calibre was becoming increasingly neglected, apart from a few exceptions such as the BAE Systems/RO Defence 105 mm Light Gun. The 155 mm calibre offers so much potential range, destructive effect and versatility that, within most armies and apart from special or airborne forces, applications for 105 mm artillery have seemingly dwindled.

Recent developments have instigated a rethink. As the prospects of full-scale warfare between major powers are reducing by the year, the need for any extensive retention of heavy artillery calibres, including 155 mm, is being increasingly questioned. 155 mm artillery is heavy, bulky, expensive and demanding in personnel, so any alternative is now being considered when it is offered.

The Denel Leo approach could be just such an alternative. It has to be emphasised that the prototype Leo was constructed merely as a technology demonstrator and was never intended to be a practical field piece in its present form. Even so, the Leo test bed promises much.

Leo is a towed, split-trail design with a 105 mm 52-calibre barrel, or 57 calibres if the rifled muzzle brake is considered. It fires a 15.8 kg high explosive, pre-formed fragment (HE-PFF) projectile to a range of 24,000 metres, considerably less than for modern 155 mm equipment, but the gun and carriage weight is less than four tonnes. That range is without BB as compatible units are still under development. It is anticipated that with BB the maximum range will increase to 30,000 metres. A combustible modular propellant charge system has been involved with Leo since its conception.

The Leo 105 mm projectiles are scaled down versions of the Assegai family, essentially having a similar profile and made from the same special high grade fragmenting steel -- the HE-PFF projectile with a proximity fuze is stated to produce a lethal radius greater than a 155 mm HE M107 projectile. In the pipeline are smoke, illumination and cargo projectiles, the latter carrying 15 dual-purpose bomblets. One unusual feature regarding Leo is that its barrel length enables it to fire 105 mm armour-piercing, fin-stabilised, discarding sabot (APFSDS) projectiles normally fired from tank guns and with similar on-target effects, considerably extending the combat potential of what was meant to be a field artillery piece.

At the time of writing it was understood that all further development of the Leo had been suspended, not for technical reasons but for the usual future financing problems. However, it is difficult to believe that the potential of the Leo will be lost.

Smart

Good as the Assegai, V-Lap and Leo projectiles might be, they remain `dumb' in that they lack `smart' target-seeking guidance. Examples of current smart system submunitions are limited to the Giat/Bofors Bonus and the Rheinmetall SMArt 155, the US M898 Sadarm having finally been laid to rest after the expenditure of many millions of dollars. Similar systems have been mentioned from within the old Eastern Bloc but they do not appear to have advanced much beyond the early development or search for technical co-operation stage. 152 and 155 mm examples of the Russian Krasnopol laser-guided projectile have been produced in quantity but no follow-on has yet appeared (although a Krasnopol technical package has been sold to Norinco of China). Any remaining US M712 Copperheads are now fast approaching (or even past) the end of their anticipated service lives.

Perhaps the main reason for this stasis is that there no longer appears to be targets for such technical marvels. All the smart systems mentioned above were intended for the attack of massed armoured formations in the event of major conflict. The chances of such formations or major conflicts ever appearing are becoming increasingly unlikely as time passes; at least as far as the few major armament procurement nations who can afford such expensive and elaborate items are concerned. Consequently, those Bonus and SMArt 155 systems already ordered and in the manufacturing process at present will probably be the last of their type, even if they are still being marketed, this time as counter-battery weapons.

Corrections

The growth in potential range has brought some novel problems in its wake. Although artillery is an area weapon, as opposed to a point contact weapon, the area to be covered to neutralise a target (the footprint) still needs to be relatively compact to be effective. At long ranges the variables that can influence a projectile trajectory become considerable, resulting in an oversized footprint and leading to the need to fire more projectiles to ensure the target is dealt with as intended. Some method of reducing such dispersions to manageable proportions is required -- and it comes in the form of trajectory correction.

Terms such as trajectory correction induce visions of guided missiles with small wings and tails, but the systems developed to date are concerned only with range alteration. Azimuth (or line) corrections are still in the future and are likely to be costly, whereas range correction is relatively straightforward and available now. However, full trajectory correction projectiles are under development. One example is the Bofors Defence 155 mm Trajectory Correctable Munition (TCM), with a number of small impulse motors around the centre of the projectile body acting in association with spring-out tail stabiliser fins. TCM testing is in progress but a service model is still some way off.

The key to both range and line correction is the Global Positioning System (GPS). GPS satellites can provide precise geographical positioning of almost any point on the ground, so if gun and target positions are known the trajectory can be calculated to keep any impact footprint `tight'. Once the projectile has been fired at high barrel elevation to a position beyond the intended target, its in-flight position can be determined with considerable precision by a GPS receiver in a fuze-sized package on the projectile nose. Micro-processors in the GPS receiver can calculate exactly when small spoiler vanes can be extended from the receiver body to ensure the vanes can affect the trajectory and make the projectile fall within the required area.

Several programmes to develop range correction systems are known to be under development but only one need be mentioned. It is the one undertaken by a consortium of Thales Missile Electronics, BAE Systems/RO Defence, Rockwell Collins, and the UK Defence Research and Evaluation-Agency (now known as QinetiQ). The consortium is known as Team Star (Smart Trajectory Artillery Round) and their product (not yet in production) resembles an ordinary nose fuze. However, that fuze body (described as a fuze upgrade) is packed with all manner of advanced electronics and associated mechanisms.

Range correction principles can also be applied to artillery rocket systems. Rockets have always been regarded as area coverage weapons but recent rocket motor propellant improvements have doubled the maximum ranges once possible, and more improvements are on the way. A typical example is the widely deployed Russian 122 mm BM-21 Grad (Hail) in its many forms. The latest BM-21 rockets can reach 20,000 metres instead of 11,000 metres, while 32,000 metres versions are on the way. At such ranges, relatively low velocity artillery rockets can be assaulted by numerous influences, so the introduction of a range correction system could be a considerable advantage.

Range correction systems are also under consideration for the MLRS, the Contraves Rheinmetall Enhancement Correction for Trajectories (known as Corect) being but one example. Similar systems have been introduced by Israel Military Industries (IMI) for its AccuLAR 160 mm rocket system. AccuLAR employs a nose-mounted gas generator to introduce course corrections so some measure of line correction could be introduced as well.

XM982

Perhaps the most complex artillery projectile currently in the pipeline is the 155 mm XM982 Excalibur under development from a US team led by Raytheon Systems. Intended to have a maximum range of some 57,000 metres when fired from the XM297 barrel of the XM2001/XM2002 Crusader advanced field artillery system (Afas), the XM982 will employ GPS-based course correction to deliver extreme accuracy at extreme ranges -- one of the planned warheads is described as a `unitary' bunker buster, implying a point target. Now that the Sadarm has been abandoned the only current alternative XM982 payload comprises dual-purpose bomblets.

The XM982 attains its range by gliding throughout much of its trajectory, using spring-out tail fins and canards to assist the process. The canards also introduce course corrections.

However, the word on the block is that the XM982 is running into the usual cost overrun problems, so we await news regarding its future.
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Author:Gander, Terry J
Publication:Armada International
Date:Apr 1, 2002
Words:2455
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