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Overstating the case: an analysis of the utility of depleted uranium in kinetic energy penetrators

A discussion paper analysing claims by the users of depleted uranium munitions that their military effectiveness overules considerations of their health and environmental impact under international law.
9 May 2012 - ICBUW

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Executive Summary

In spite of longstanding concerns over their toxic and radioactive properties, depleted uranium (DU) weapons are retained by around 20 countries worldwide, primarily as kinetic energy weapons. Governments that use DU as a penetrator material often defend this choice by stating that its ability to penetrate armour is significantly greater than alternative materials.

ICBUW, and others, have questioned the legality of DU weapons, but in the past this debate has generally been restricted to the humanitarian and environmental effects of DU, rather than the military utility of DU weapons. This paper is intended to address the other side of the debate, to critically assess and to give some context to claims about the military utility of weapons containing DU.

While DU weapons do confer some military advantage, this advantage can also be gained through other means: DU does not therefore confer a unique military advantage. Thus, greater emphasis should be placed on humanitarian and environmental concerns when examining DU’s acceptability.


How effective is depleted uranium at piercing armour?
The reason that DU is considered to be so effective as a penetrator material is that it combines high strength and density with a type of deformation on impact known as 'adiabatic sheer'. While other penetrator materials (chiefly different alloys of tungsten) are of a comparable density to DU, they exhibit different deformation and fracture behaviours.

It is difficult to find information in the public domain about the effectiveness of DU and information that makes an exact comparison with other materials is even more difficult to access. However, internal UK government documents cite an improvement of about 15% in performance. A US government document suggests that DU offered an average of a 52% increase in penetration above that of the tungsten alloys.

These figures will not necessarily hold true for modern tungsten alloys, or indeed modern types of armour. Nevertheless, it seems reasonable to treat them as indicative and conclude that on a strict material-to-material comparison, DU is better at penetrating armour than presently available alternatives. However it seems likely that DU's advantages as a material will be matched at some stage by new compounds. A 2009 review of alternative materials by staff from the US Army Research Laboratory identified nanocrystalline tungsten and bulk metallic glasses (BMG) as showing promise in key areas.


Other variables determining effectiveness of kinetic energy rounds
Penetrator material is only one among many variables which determine the effectiveness of a kinetic energy round. Although DU appears to be the most effective material, it is quite possible to achieve similar improvements in performance by other means.

Other significant variables that can be adjusted to increase the effectiveness of armour piercing rounds include the dimensions and shape of the penetrator. Reducing the weight or other performance-improving changes to the sabot can increase velocity, as can modifications to the barrel or improvements to the explosive charge.

It appears that modifications to the round, gun or other factors, which are unconnected to the choice of penetrator material, will often give more significant improvements to performance than changing penetrator material.


Wider determinants of tank warfare effectiveness
The anti-armour capability of tanks is dependent on numerous variables besides the basic engineering characteristics of the ammunition and gun. The accuracy of a shot, the speed at which it can be fired in response to sighting an enemy and the rate of fire can all play a critical role in tank-on-tank confrontations.

Few, if any, of the criteria which contribute to the anti-armour capability of tanks are so significant that any comparative disadvantages in that field cannot be offset by gains in another. Certainly this is not the case when selecting penetrator material.


The best material for the job?

A historical case study of the development of the British CHARM rounds and Challenger 1 tank
While a simple conception of ammunition development might state that the most effective material should always be chosen, in reality, procurement and development decisions are more complicated. This is well illustrated by the case study of the British Challenger 1 tank and the DU rounds developed for it.

Anti-armour tank ammunition is designed to defeat specific armour configurations. It is judged against its ability to defeat a range of armour fielded by potential enemies and on predictions of future enemy armour developments.

In the late 1970s, efforts to develop a common US, UK and German tank gun failed and the UK planned to develop a new tank on its own with a 120mm rifled gun. However, due to a combination of external circumstances, it was decided that the UK would purchase a derivative of the Chieftain tank, to be known as Challenger 1.

A DU round and a new high pressure gun were planned following projections of the type of armour expected in the successor to the Soviet T80 tank, but the gun would still be compatible with the Chieftain ammunition already in service. UK DU ammunition was developed because it was deemed necessary for defeating a particular type of armour and circumstances had limited the possibilities for adjusting other characteristics of the weapons system without a considerable investment of time and money.


Consequences for present day UK tank ammunition
Problems with the Challenger 1 tank necessitated an upgrade to the whole UK tank fleet. The updated tank, known as the Challenger 2, featured the high pressure gun, and a high pressure DU round, known as CHARM 3. This round finally became available in 1999 and remains the UK’s main anti-armour tank ammunition.

Rather than the brand new tank envisaged by military planners in the early 70s, the UK is fielding a tank with a gun that is the result of evolutionary adaptations from the Chieftain, where backwards compatibility has been a consideration at each stage. As a result, design of the CHARM 3 round is determined in part by decisions taken for a tank which first came into service in 1965. The limitations of this round and the lack of an export market have prevented any further development of UK armour piercing ammunition.


Lessons from the CHARM case study
Rather than starting with a blank slate and choosing the best material for the job, ammunition and procurement decisions are taken within a wider political and economic context, which may be considerably more important in determining round characteristics.

Since around 2002, UK planners have recognised that for reasons of cost and compatibility, future British tank ammunition should be compatible with other NATO countries. However, a planned improvement involving non-DU ammunition, which has apparently proven to be more effective than CHARM 3 ammunition, has not been implemented for reasons of cost.

The UK’s switch to DU ammunition allowed them a ‘one-off’ increase in penetration, meaning that other procurement decisions could be taken for reasons of backwards compatibility and to support the British defence industry, rather than maximising effectiveness. However, in the long run, this has not prevented the round from becoming less effective than the non-DU system used by Germany.


The factors affecting ammunition design and penetrator material choice are far removed from a simple case of choosing the ammunition with the greatest possible military utility. Although straightforward engineering principles will inform the decision, wider considerations may be much more significant.

It is technically possible to design weapon systems that are equally as effective as DU using alternative materials. This is particularly true in the post Cold War era when the arms race between different armours and penetrators has largely ceased. All that is required is the political will for change within user states.

Although DU may, on consideration of penetrator material alone, be better at penetrating armour, this advantage is not so great that other adaptations cannot be substituted. When considered in light of the numerous disadvantages of using DU, ICBUW believes the perceived benefits well outweigh the costs.

There are some indications that this point of view is spreading from the many countries that have never sought to use DU weapons, to some of the states which were previously the most enthusiastic, with recent reports that the US is planning to develop a non-DU successor to its current 120mm DU round.

While DU may at present be the most effective penetrator material in a strict material-to-material comparison, this does not mean that DU ammunition is so militarily useful that alternatives cannot be found, given sufficient resources and political will. In light of the numerous problems regarding DU as a material, the case for user states to abandon these weapons is unanswerable.