Deterring Chemical, Biological, Radiological, Nuclear, and High-Energy Weapons Use in the War Against Terrorism: 

The Moral Dimension


by Lieutenant Colonel John Mark Mattox, US Army

Supreme Headquarters Allied Powers Europe


The Changing Face of Deterrence


Almost twenty years ago, during the Cold War, philosopher Sir Anthony Kenny wrote, “Deterrence is the key concept for the understanding of the strategy and diplomacy of the age.  It is a concept which is used to justify decisions of high cost and great moment.  Deterrence is a simple idea, but like many simple ideas it has a complicated logic.”[1] Indeed, its logic is complicated.  Moreover, the face of deterrence is changing.  Today, I wish to defend the thesis that, for the first time in half a century, the West cannot rely completely upon a strategy of deterrence as it was understood during the Cold War to protect it from the threatened use of chemical, biological, radiological, nuclear, and high-energy weapons (now frequently referred to as CBRNE weapons).  For students of moral philosophy confronted with the challenges of countering terrorism, the ramifications of this thesis are of great consequence and worthy of careful reflection. 


What is “Deterrence”?

In the present context, by “deterrence” I mean the ability to dissuade an acknowledged or a potential adversary from using CBRNE weapons by implicitly or explicitly threatening retaliation, usually in kind.  Of course, broader understandings of deterrence exist, but because of the unique problems associated with CBRNE weapons, we shall limit our discussion of deterrence to how it applies to these weapons.  Understanding this definition is important because much of the literature on nuclear weapons, and to a lesser extent on biological and chemical weapons, has assumed that deterrence thus or similarly defined is the key to preventing an angry exchange involving them.  Radiological weapons (that is, weapons designed to disperse radioactive materials as contaminants), when discussed at all, traditionally have been included under the general rubric of nuclear weapons.  However, the present reality that terrorist organizations are seeking access to CBRNE weapons has resulted in a renewed concern over radiological weapons in their own right.  Similarly, high-energy mechanisms, while technically “conventional” in nature, have assumed a new level of importance since such weapons now include not only theatre ballistic missiles, but also Oklahoma City-style truck bombs and large commercial aircraft laden with fuel and used in kamikaze-style attacks. 

In addition to understanding what deterrence is, it is worth considering what made CBRNE weapon deterrence—particularly nuclear deterrence—work during the Cold War.  It seems clear that deterrence required three things:

  First, deterrence required the physical presence of deployed weaponry and not mere bluff or threat.  It is precisely for this reason that some nations possessing CBRNE weapons historically elected to “showcase” them so as to convince other nations that the weapons really existed.  (Recall, for example, the endless procession of Soviet nuclear weapons on Red Square during annual May Day parades.) 

Some may argue that physical presence was not actually required.  Rather, they may hold that the mere belief in an adversary’s mind that the weapons were deployed was sufficient to deter.  However, an argument of this kind seems to confuse deterrence with deception.  Indeed, merely pretending to have the weapons might have dissuaded an adversary in the short term.  However, given the increasingly sophisticated means available for surveillance and intelligence gathering—not to mention the various international inspection regimes designed to reveal the likely presence of CBRNE weapons—it is rather unlikely that an adversary could have been deceived in the long term. 

Second, the deterrent had to be credible.  That is to say, merely the known possession of  CBRNE weaponry was not enough, and even the possession of superior numbers of CBRNE weapons could not, in and of itself, ensure the success of a deterrence strategy.[2]  Rather, the possessor also had to possess the capability to deliver the weapon in a way that posed a threat.  For this reason, even a nuclear power (as, for example, South Africa used to be) could not have been said to possess a nuclear “deterrent”—except perhaps against its immediate neighbors—in the relevant sense.

Third, those with their fingers on the triggers had to be seen to possess the political will to pull the triggers if deterrence failed.


Deterrence Then and Now

The world that gave rise to this understanding of deterrence was a bipolar world consisting of the Warsaw Pact (read the Soviet Union) and the North Atlantic Treaty Organization (read the United States).  Those who lived through the Cold War and remember the fears that arose from the thought that, in thirty minutes, intercontinental ballistic missiles from the other side of the planet could be directly overhead, may have taken some solace from the concept of deterrence. After all, the idea of mutual assured destruction in any of its various policy incarnations should have been enough to deter any rational actor from attacking the other side; and, if rationality failed, there was always the warm, fuzzy realization that the instigator would live only long enough to regret his decision to launch.

However, the world today is not merely a little different from the world of the Cold War; it is radically different.  Almost nothing remains of Cold War bipolarity.  There is no United States-Soviet Union dichotomy because there is no Soviet Union.  There is no NATO-Warsaw Pact dichotomy because there is no Warsaw Pact.  In fact, with the formation last year of the NATO-Russia Council, it would appear that the old enemy is now the West’s new friend, and the new enemy is the somewhat elusive “axis of evil.”  As a matter of current U.S. policy, that includes Iran, Iraq, Syria, and North Korea, but it might be more generally construed to mean forces that pose a threat to NATO and, presumably, to Russian interests as well, wherever those forces may appear.  The trouble is that there seem to be so many forces of that description!    What is worse, many of those forces have or aspire to have CBRNE weapons.  Moreover—and this is the aspect of the problem that concerns us here today—many of those forces are terrorist in nature.  Those forces may or may not be states in the Westphalian sense, and they are willing to take extraordinary risks, to include tactics that necessarily involve self-destruction.


The Moral Problem with Deterrence

During the Cold War, there was some tendency for moral philosophers to decry deterrence on all but utilitarian grounds.  However, for those willing to wax utilitarian, deterrence seemed to be morally justifiable because it could be argued that deterrence contributed greatly toward the aim of averting world-altering politico-military catastrophe.  As is sometimes the case in utilitarian logic, the theory of deterrence was understood to include the willingness to underwrite a certain evil (namely, the threat of utter destruction) in order to secure a potential good (namely, the hope that catastrophe would be avoided altogether).

Let us proceed on the premise that deterrence is, as utilitarians might claim, a morally defensible idea.  However philosophically messy and problematic that claim may be, it is one which—short of a transcendental solution—seems to trump all others in the Hobbsian state of nature (an apt model for much of what happens in international relations).  For that matter, note that many models which are based on deterrence, but which have nothing to do with CBRNE weapons, are found in the domestic relations of all societies.  Indeed, every edict of every legal code was written with the idea of deterrence in mind.  The idea always has been to dissuade human beings from pursuing self-interests beyond the bounds of reasonable toleration by threatening them with a penalty that would induce a greater balance of pain (to appropriate the language of Mill) than any pleasure they could obtain by the unbounded pursuit of self-interests. 

Deterrence, like many other widely practiced social arrangements, assumes that all agents will play by essentially the same set of rules; there is no provision for agents to act outside the framework of the system.  In contrast, terrorism involves agents who are committed to deliberate action outside the framework of the system that deterrence was designed to constrain.  Trying to deal effectively with the acts of terrorists who, by definition, operate outside of the system is already a daunting task.  However, when those terrorists possess CBRNE weapons, the problem becomes particularly intractable because of the destructive potential of these weapons.

Deterrence and Terrorism

            At the heart of the issue are two questions.  First: 

If deterrence finds its moral-philosophical defense in the claim that the threat of retributive violence dissuades potential adversaries, is it still defensible if the threat of violence fails to dissuade terrorists from using CBRNE weapons?


There may be some hope that deterrence will prove efficacious in the case of CBNRE terrorist acts either perpetrated or overtly sponsored by states.  These states, faced with the possibility of large-scale (perhaps even nuclear) retaliation would have reason to be hesitant; and the reason is an old one, woven deeply into the fabric of the Western worldview.  It is that states can be counted on to act in self-preserving ways.  As Cicero argues, nothing is worse than the death of the state.  In his view, the state’s preservation is essential to the moral and physical well being of the human race.  Hence, the death of any person—no matter how great the person may be—is less to be lamented than the extinction of the state.  Indeed, “there is some similarity,” Cicero argues, “between the overthrow, destruction, and extinction of a State, and the decay and dissolution of the whole universe.”[3]

Unfortunately, Cicero’s rationale serves also to highlight the problem associated with deterring terrorists who either are not overtly state sponsored or else are not state sponsored at all.  In these cases, there is no state whose death is at risk; and, indeed many terrorist groups embrace ideologies that hold that the death of individual actors is not to be lamented at all, provided that their departure from this present world is accompanied by their wreaking terrorist havoc in the name of their cause. The thought that the commission of terrorist acts will result in a martyr’s reward in eternity is hardly a deterrent to terrorist action.  Indeed, it would seem that the terrorists of September 11, 2001, either did not read Cicero, or, perhaps worse, they did read Cicero and deduced thereby how to press beyond bounds that most Westerners are unwilling to transgress.  This reality poses an enormous problem for the traditional notion of deterrence, because deterrence assumes—indeed must assume—that the adversary will not submit to the possibility of self-destruction.  Indeed, it is this reality more than any other that constitutes a defense of the thesis that the traditional concept of deterrence cannot be expected to prevent the use of CBRNE weapons by terrorists whose ties with states are at best tenuous or informal.

This conclusion leads naturally to the second question at the heart of the present issue:

If, deterrence having failed, terrorists use CBRNE weapons, is a military response morally permissible?


To begin, it seems clear that any military response must meet the jus in bello test of “proportionality.”  Ironically, as disproportionate as a massive Cold War superpower CBRNE exchange may have been, that exchange itself had a grotesque proportionality to it; that is to say, each side was able to annihilate the other, and therefore each kept the other in check.  Terrorists, on the other hand, seek to achieve vastly disproportionate results in terms of body count, even if their own lives are lost in the process.  There is significant incentive for the terrorist to act disproportionately.  Terrorists do not seek CBRNE weapons in order to maintain some balance in the world order.  Rather, they seek to destroy the world order or important aspects of it. 

Having so said, of what might a proportional military response to terrorism consist?  At present, various governments and international agencies, to include NATO, are taking measures, including the creation of CBRNE crisis response teams, to deal with the eventuality of CBRNE terrorist attacks.  This is an important first step; for, in the light of the abiding requirement for proportionality, an appropriate initial response to CBRNE terrorism should include heightened security measures, individual protective clothing or other prophylactic measures, all of which are designed to mitigate the effects of a CBRNE attack.  We should note that steps like these have some deterrent value.  For, while perfect deterrence cannot be assured against terrorists willing to sacrifice their lives for their cause, those same terrorists may feel dissuaded if they perceive that the safeguards erected between them and their target population are such that the sacrifice of terrorist lives would not yield a sufficient payoff.  Hence, it is arguable that not only are such preventive measures morally praiseworthy for their deterrent value, they are in fact morally required.

By the same token, it is doubtful that such measures could be understood to constitute an entirely adequate response—morally or otherwise—to CBRNE terrorism.  Indeed, the work of a CBRNE crisis response team is analogous to the placement of a gauze bandage on a sucking chest wound:  a soldier would not want to be without the bandage if the need arose, but merely applying such a bandage is not a proportionate response to the magnitude of the injury and no response at all to the cause.

            Most probably would agree that domestic acts of terrorism to not warrant an uninvited international response.  However, let us assume that a terrorist—state-sponsored or otherwise—commits a terrorist act across international borders using CBRNE weapons.  If the perpetrator could be identified beyond reasonable doubt, then strenuous exertions to bring the perpetrator to justice—including the possibility of either a conventional or appropriately constrained nuclear attack upon key nodes of the terrorist organization—seem not to be morally problematic. 

At this point, it is important to distinguish clearly between the moral-philosophical and the practical dimensions of the problem.  For example, questions such as whether one state can enter another state in pursuit of terrorists without the latter’s permission are primarily political or legal matters—not necessarily moral ones.  Similarly, emotional cries to the effect that it is impossible to target terrorists precisely and without appreciable collateral effects highlight important technological issues, but again, not necessarily moral ones.  What is politically acceptable or legally permissible today may not be tomorrow and vice-versa.  Similarly, if an appropriately surgical conventional or nuclear response to certain targets is not now possible, advancing technology may render it possible, thereby assuring that the responding governments, commanders, and targeteers can respect their moral and legal responsibilities toward non-combatants.


Pre-emptive Action

Cold War conventional wisdom exhorted deterrence by suggesting that “an ounce of prevention is worth a pound of cure.”  Unfortunately, resources by the ounce are insufficient to prevent the use or to mitigate the effects of CBRNE weapons. The preventive measures are monumentally expensive—in many cases, more so than the weapons themselves.  Hence, if preventive measures are not sufficient to deter terrorists from action, the question naturally arises concerning the moral propriety of a pre-emptive action against agencies that evidence a capacity, willingness, or intent to use CBRNE weapons. 

By way of clarification, one should take care to distinguish between a so-called “preventive war” and a “pre-emptive action.”  These terms are not used consistently in professional literature, and so the following distinction is made for present purposes:  A preventive war is one that is initiated before any immediate threat of hostilities with an eye toward overpowering a potential opponent so that the opponent cannot strike.  A pre-emptive action, on the other hand, is one in which an adversary has set in motion the chain of events that is reasonably judged to lead inevitably to a yet unconsummated attack.[4]

Historically, just war theory has maintained a prohibition against what we are calling preventive wars and at least a strong prima facie presumption against the moral permissibility of what we are calling pre-emptive action.  However, it may be that terrorist acts fall outside the scope of this negative presumption.  The terrorist use of CBRNE weapons typically involves the unconstrained and indiscriminate killing of non-combatants with substances whose best or only use is to produce death or destruction.  Many Western societies arrest and impose criminal sanctions upon persons who possess, without legal license, substances regarded as inherently harmful (such as narcotics, etc.), and whose illicit possession can only be malevolent.  Perhaps the same standard might be applied to terrorists groups possessing or seeking to possess the essential components for CBRNE weapons.  If, for example, clandestine plans to perpetrate a CBRNE attack were discovered and those involved were identified with sufficiently high resolution, there may well exist grounds on which an appropriately constrained military action of some sort is morally permissible.  Viewed in this way, if the offense against law and morality consists in the mere illicit possession of substances whose sole or primary use can only be malevolent, then to act against the possessor is not, strictly speaking, “pre-emptive” at all.  Rather, it is a retributive act against one who already has committed an offense.


How to Respond

 Assuming, then, that it is morally permissible to respond to a CBRNE terrorist attack—perhaps even to the point of responding “pre-emptively” in the sense just described (i.e., after one has obtained the components for, demonstrated both capacity and intent to use, but before one actually has detonated, a CBRNE weapon)—one final question arises:

What attack mechanism could be used with moral justification to respond to terrorist use of CBRNE weapons?


The initial reaction might be to respond “in kind.”  In fact, much of the literature on CBRNE banters around the phrase “response in kind” as if this really were possible, when in fact a “response in kind” generally is either technically infeasible or politically or morally inappropriate.  Consider the following:

With respect to radiological weapons, no morally permissible retaliation in kind is conceivable.  Radiological weapons of the kind that concern us are terrorist weapons par excellence; they scatter radioactive debris in ways that can result in long-term and utterly indiscriminate effects.

With respect to biological and chemical weapons, the nations of the Western Alliance possess no “in kind” retaliatory capability whatsoever.  They have divested, or are in the process of divesting, themselves of all offensive biological and chemical weapons.  Whatever residual capability remains beyond that earmarked for destruction is for research purposes only and in such quantities that its use for offensive purposes would not be effective.  This means that, for all practical purposes, the West could retaliate militarily against the terrorist use of radiological, biological, or chemical weapons in two ways only:  either with nuclear weapons or with conventional weapons.  

A response in kind with high-energy weapons is possible, but only with qualifications.  Of course, a response in kind to the attacks of September 11, 2001, would be unthinkable.  However, it is readily conceivable that a standard “high-energy” conventional munition (such as the so-called “daisy cutter” bomb used in Afghanistan) could be used, if technically appropriate for the target and taking collateral effects into account, as a response “in kind” without the need for hesitancy on moral grounds.  It should be noted that high-energy precision weapons, far more elegant in their operation than the daisy cutter, are now on or beyond the drawing board and potentially will obviate the need for many present concerns over collateral damage.

A response in kind with nuclear weapons is possible, and this is what many authors actually have in mind when they rather carelessly invoke the phrase “in kind” with respect to CBRNE weapons.  There are good and prudent reasons to reserve the right to respond “in kind” to a nuclear attack.  First, state sponsors of terrorists may be very reluctant to risk using nuclear weapons precisely because they do not want an in-kind response.  In this case, traditional deterrence still might prove to be an effective tool.  Second, there still are targets in the world for which nuclear weapons provide the most effective attack mechanism.  For example, even non-state-sponsored terrorists require some kind of infrastructure if they intend to use CBRNE weapons, and attacks on their CBRNE infrastructure may, in certain cases, be most appropriately conducted with nuclear weapons.  Unfortunately, as already noted, attacking such facilities only after the fact does little or nothing to deter the terrorist who is willing to “go for broke” with the realization that his infrastructure may not last very long after his initial use of CBRNE weapons.  Hence, even here, responding in kind may do little to deter the terrorist, and this in turn may serve as an argument for some kind of carefully constrained pre-emptive action.

In the light of the foregoing, it should be plain that much of what is written on the matter of in-kind responses to CBRNE attacks is not very helpful.  As students of moral philosophy, we recognize that there is no particular moral imperative to respond in kind—in degree, perhaps, but not necessarily in kind.  The requirement for responding to terrorist preparations or actions is merely that the response, whether pre-emptive or after the fact, should be appropriate in technical, political, and moral terms.


            In sum, the present threat of terrorism poses a very different set of challenges from those encountered during the Cold War—especially as pertaining to the threatened use of CBRNE weapons.  Hence, while our moral sensibilities need not and indeed should not change, we must take into account the reality that the lawless terrorists that threaten the West appear to have no intention to play by the traditional rules that for centuries have governed the just conduct of war.  Make no mistake:  that does not mean that the West should feel at liberty to wage war without moral constraint.  Rather, it means that we must reassess how much malevolent preparation we are willing to tolerate from known terrorists before we consider that action is morally justifiable.  Indeed, in the age of swords, one did not respond until a sword was raised.  In the age of gunpowder, one waited until a shot was fired.  The question before us now is, in the age of terrorists armed or seeking to be armed with CBRNE weapons, what constitutes an intolerable offense and how long does morality require that we wait before we respond?

Whatever the answer to these questions, it would seem that the time has come to expand the search for morally acceptable solutions in combating CBRNE terrorism, for we can no longer depend upon the traditional notion of deterrence to make the search unnecessary.[5]



[1] Anthony Kenny, The Logic of Deterrence (Chicago:  The University of Chicago Press, 1985), ix.

[2] See Bernard Brodie, Strategy in the Missile Age (Princeton:  Princeton University Press, 1965), 274.

[3] Marcus Tullius Cicero, De Re Publica III.xxiii, in De Re Publica and De Legibus, trans. C. W. Keyes (Cambridge:  Harvard University Press, 1928):  211-213.

[4] See Brodie, 242.

[5] I am indebted to U.S. Army Colonel (Retired) John Robbins, U.S. Air Force Colonel (Retired) Henry Keese, and Dr. Joseph Wolfsheimer of the Defense Threat Reduction Agency Field Office, Chievres, Belgium, for their review of preliminary versions of this paper and for their invaluable insights.