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In our daily lives, we often make decisions and take actions that have unintended consequences. When these unintended consequences translate into someone or something being damaged, they are known as “collateral damage”. 

Collateral damage can have a significant impact on us and others, both in the short and long term. In military contexts, the term “collateral damage” refers to harm or damage caused to civilians or civilian infrastructure during military operations. The concept can also be used more broadly in other contexts, such as politics, economics, and personal relationships, proving it is just a part of life and unavoidable. This is, of course, not an excuse for legitimizing it but, as a matter of fact, humans do not have the capability to remove the chance of collateral damage or unintended consequences in every aspect of their lives. Collateral damage is a concept that proves relevant to many aspects of our lives, from personal relationships to global events. Only by being mindful of the potential unintended consequences of our actions can we take steps to minimize – not eliminate – the possibility of causing collateral damage and create more positive outcomes for ourselves and others. 

In military operations, the imperative of minimizing collateral damage is intimately linked with that of protecting civilians. Protection of civilians and civilian property is founded in the universally accepted rules of international humanitarian law, human rights and refugee law, which are set out in a range of international legal instruments. The most important of these are the Geneva Conventions of 12 August 1949, in particular the Fourth Convention, and their 1977 Additional Protocol I relating to the Protection of Victims of International Armed Conflicts and Protocol II relating to the Protection of Victims of Non-International Armed Conflicts. Collateral damage is becoming more and more relevant because it is a stark reality of contemporary theatres of war. Regardless of the moral integrity of all the actors operating in contemporary war scenarios, where collateral damage is often intentionally caused, NATO Alliance Nations and their military units refrain from deliberately causing collateral damage and have in place numerous procedures to minimize it, in adherence to and inspired by the Law of Armed Conflicts (LOAC).

All the relevant international legislation, most fundamentally, dictates that civilians and civilian objects are protected from both direct and indiscriminate attacks. The most significant practical protection for civilians and civilian objects, however, comes with the requirement for everyone to take precautions in conducting military operations, which in practice translates into exploring and assessing all the available operational options. Attackers must take all feasible measures to verify that the target is a lawful military target. They must also consider feasible targets, tactics, and weapons options that achieve the desired effects of the operation (the “military advantage” in LOAC terms) while limiting collateral damage. And attackers must precede their attacks with warnings if the circumstances permit. 

Once all the possible precautions have been explored and all of them that can be applied have been applied, an attacker must then evaluate proportionality. According to the rule of proportionality, attacks are prohibited against military objectives if the attack is expected to cause incidental harm to civilians or civilian objects that would be excessive in relation to the concrete and direct military advantage that can reasonably be anticipated. Thus, proportionality determinations are made before an attack will be conducted and not during the attack, on the base of the intelligence available at the time; in other words, the determinative factors are what the attacker knew, or should have known, regarding collateral damage and what military advantage the attacker reasonably expected to achieve. 

The principle of proportionality closely resembles and is likely based on the “Doctrine of Double Effect” (DDE), a theory of moral philosophy that dates to Thomas Aquinas. This theory states, in general terms, that an act may be morally permitted, despite causing bad consequences, provided that the act itself is directed at achieving a moral good, the actor intends solely to achieve that moral good, the bad consequence is not a means to produce the moral good and finally the positive intended effects outweigh the unintended negative ones. Compliance with these rules constitutes a huge burden for units and staffs and can seriously challenge leadership freedom of action. While conducting military operations, the imperative of minimizing collateral damage is operationalized in the first instance through guidance imposed by higher echelons of command. Other concurrent ways for the military to address collateral damage are the implementation of analytical processes designed to assess the likelihood of collateral damage, and the use of technologies that offer better precision, greater clarity in the battlespace, and redundant capabilities. The most common way of delivering guidance on collateral damage prevention in the military is the use of rules of engagement (ROE) to restrict the application of force during armed conflict. ROE are the result of the fusion and the best achievable compromise between military, political and legal restraints or constraints. The use of no-strike and restricted target lists also contribute to detailing guidance on the avoidance of civilian harm. No-strike lists (NSL) identify objects, termed “no-strike entities,” that are non-military and protected from the effects of military operations. Restricted target lists (RTL) are likewise developed to mitigate civilian harm. They differ from NSLs in the sense that restricted targets are valid military objectives, but restrictions are placed on attacking them for various reasons, as in restricting damage to a bridge that needs to be crossed by friendly forces later in the conflict. The last key piece of guidance aimed at minimizing civilian harm is the requirement of a positive identification (PID) of a target before its engagement. This requirement is satisfied when there is “reasonable certainty” that the proposed target is a legitimate military objective. 

Among the various processes employed to avoid collateral damage during military operations, the most important is the Collateral Damage Estimation Methodology (CDEM). Developed by the US military on the basis of experimental measurements of weapon effects produced by the entire spectrum of the US inventory of weapons, CDEM is a logical and repeatable analytical process used by military planners to assess and estimate the potential impact and consequences of an attack on a target; it aims to predict and quantify the potential collateral damage, including civilian casualties, damage to infrastructure, and other unintended effects that may result from military operations. 

The methodology is designed to provide a credible estimation, not a verdict, on the potential for collateral damage, to enable the identification of possible and alternative courses of action for attacking a target, based on the associated level of risk, thereby allowing commanders to understand, consider and mitigate risks. In its practical use, the CDEM is used to identify any “collateral concerns” (i.e., civilians, civilian objects, or other protected objects) within the collateral effects radius (CER) of the warhead, weapon, or weapon class (a circle outlining the furthest line the effects of a weapon can reach) being considered for use in the attack. 

If collateral concerns are present within the CER, progressively more demanding mitigation techniques are used to protect such concerns from weapon effects and then progressive collateral damage thresholds or CDE levels will be dictated, which will progressively restrict courses of action to engage the target, while minimizing the chance of collateral damage. Should collateral concerns within the CER still exist after mitigation techniques have been exhausted, CDEM provides a numeric estimate of the number of civilians who may be injured or killed if the attack goes forward. This estimate will then be used to determine if the attack can proceed under any circumstances at all (e.g., whether it is prohibited because it will be disproportionate under LOAC) and, if it can, who may approve the attack. 

In conclusion, we acknowledge that the mere existence of the guidance, processes, and technologies to avoid civilian harm described above does not solve the tragedy of collateral damage. They must be employed in good faith and with a pervasive commitment to avoiding collateral damage whenever possible. That said, civilian casualties do not necessarily equate to a failure to comply with LOAC or apply best practices in civilian casualty minimization on the battlefield. NATO forces take exceptional measures to reduce the pain inflicted by war, but this does not necessarily mean that we will always be successful.