Biometrics on the Battlefield


| Oct 21, 2020


We use biometrics on a daily basis. You need only think of unlocking your phone with your fingerprint, using iris recognition to pass through airport security, or the biometrics integrated into your passport.

Considering the possibilities this technology offers, its increasing use by armed forces is unsurprising. On the modern battlefield, parties to armed conflict—particularly terrorist groups—often rely on anonymity. Biometrics can be a powerful tool to deny that anonymity.

As with other relatively new technologies, biometrics raises questions regarding how existing law can regulate its use and whether the law needs to be supplemented. The international legal regimes most relevant to the general use of biometrics include international human rights law and data protection law. The use of biometrics during armed conflict, however, would also implicate international humanitarian law (IHL).

This post seeks to explore the relationship between IHL and biometrics. It will first briefly describe the technology and its possible uses by armed forces. It will then discuss how the use of biometrics could contribute to better IHL compliance. Lastly, it will attempt to identify IHL rules that could affect whether and how this technology may be employed during armed conflict.

What is Biometrics?

The NATO definition of Biometrics is “automated recognition of individuals based on their behavioral and biological characteristics.”[1] Examples include finger and hand topography, iris structure, DNA, voice dynamics, and gait. Repeatable biometric features can be extracted from these characteristics to facilitate biometric recognition. Recognition involves various steps, including enrolment and identification or verification.

Enrolment is the act of creating and storing someone’s biometric feature. The process by which one compares that feature to those of all individuals previously stored is known as identification. Through the verification process, an individual’s feature is compared to his own stored biometric file. This latter step helps determine whether an individual is who he claims to be and can help identify those deceased.

Biometrics in Military Operations

Biometrics can be used in a variety of ways during military operations. It can, for example, be employed to control access to a military installation by verifying that only authorized individuals are granted such access. Another use could include identifying individuals considered to pose a threat to friendly forces. Biometric technology was used in this manner during operations in Afghanistan and Iraq. Among other uses, devices capable of biometrically identifying persons were employed at check points and by units on patrol to scan persons whom they encountered. Associated with this use is the possibility of employing biometrics for the purpose of kinetic targeting from the air, in other words in a stand-off situation. Voice recognition, for example, has reportedly been used in the context of drone strikes.

Biometrics and International Humanitarian Law

The principal IHL treaties date from 1949 and 1977. It is therefore unsurprising that they do not specially address biometrics—a technology developed in the last few decades. This does not necessarily mean that IHL is silent on the use of biometrics. In principle, the law is expressed in technologically neutral terms. As the International Court of Justice famously said in its Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, IHL “applies to all forms of warfare and to all kinds of weapons, those of past, those of the present, and those of the future” (para. 86). This statement not only applies to weapons technology but also to other technologies that are introduced on the battlefield.

Biometrics and Increased IHL Compliance

Identification is key to compliance with IHL. One of the most important principles of IHL is the principle of distinction. This principle—which has been codified in Article 48 of Additional Protocol I and forms part of customary international law—requires parties to an armed conflict to distinguish between civilians and combatants at all times. A logical corollary is that civilians may not be made the object of an attack. Another is that those who plan or decide upon an attack must do everything feasible to verify that an objective to be attacked is not a civilian.

Reliable identification or verification of individuals is therefore of vital importance under IHL. Biometrics can contribute to this—particularly in cases concerning known individuals—by helping to ensure that the right person is targeted. As was mentioned before, it appears that voice recognition technology has already been used for this purpose. Other biometric characteristics such as facial recognition and gait could also be used similarly.

Although biometrics can offer more certainty than was previously available about someone’s identity, not all uses of biometrics will necessarily lead to better compliance. In reality the technology is not infallible. A biometric system can merely provide a score indicating the degree of certainty of a match. Many factors impact the reliability of the technology, some relating to the technology itself and others to the environment in which it is employed.

This can lead to two kinds of errors in the outcome of a biometric process. One type of error can occur when the technology fails to identify a person already enrolled (also referred to as a “false negative”). The other type transpires when an erroneous match is made, thus misidentifying a person (also referred to as a “false positive”). The latter can clearly have serious repercussions for compliance with the principle of distinction. Combining different biometric characteristics (so-called “multi-modal biometrics”) can mitigate the risk of false positives. However, their occurrence cannot be excluded.

Biometrics can also contribute to the identification of persons outside the context of targeting. Geneva Conventions III and IV provide for the institution by parties to an armed conflict of national information bureaux. These bureaux function to collect information on POWs and civilians and to exchange that information with other concerned Powers. If biometric information were included as part of the information exchange, the identification of the missing and dead could be made easier and the process of informing next of kin facilitated.

Whether and How Biometrics may be Employed during Armed Conflict

IHL is primarily of a prohibitive nature. Although there are no provisions in IHL treaties that address biometrics as such, let alone prohibit its use, there are a number of rules that arguably limit whether and how biometric enrolment may take place.

Article 17 of the Third Geneva Convention, for example, provides that every POW, “when questioned on the subject, is bound to give only his surname, first names and rank, date of birth, and army, regimental, personal or serial number, or failing this, equivalent information.” The article continues by stating that if a POW “willfully infringes this rule,” the only possible sanction is a restriction of the privileges accorded to his rank or status. This means that other sanctions are not allowed, arguably including compelling the POW to give information in the form of his biometric characteristics.

The updated ICRC commentary to Article 17 only mentions the possibility of using biometrics in connection with paragraph 5 of the article (para. 1833). That paragraph provides that the identity of POWs who, “owing to their physical or mental condition, are unable to state their identity … shall be established by all possible means.” This suggests biometrics may be used in the case of that particular category of POWs, but not when POWs are able to provide information concerning their identity but decline to do so.

Article 31 of the Fourth Geneva Convention states, “No physical or moral coercion shall be exercised against protected persons, in particular to obtain information from them or from third parties.” This can arguably be read as also prohibiting compelling civilians to be biometrically enrolled. The ICRC commentary states that the coercion referred to in the article is coercion for any purpose or whatever motive.

Article 27 of the Fourth Geneva Convention provides that “protected persons are entitled, in all circumstances, to respect for their persons.” According to the ICRC commentary, this covers “in particular the right to physical, moral and intellectual integrity.” If this right would include a right to privacy, the article would limit the possibilities for biometric enrolment. However, as far as I am aware this is not how the article is interpreted. Separately, Article 27 states that the parties to the conflict “may take such measures of control and security in regard to protected persons as may be necessary as a result of the war.” One could argue that such measures may include biometric enrolment. However, this does not affect the obligation to respect the fundamental rights of protected persons which must be respected “in all circumstances,” as set out in the aforementioned article.


In legal terms, biometrics on the battlefield is a double-edged sword. On the one hand, as discussed above, it has the potential to improve compliance with IHL, in particular with regard to the principle of distinction.

On the other hand, the technology can have serious repercussions for the privacy of the population in conflict areas. As shown above, IHL contains only a few provisions that arguably address this aspect of biometrics. Moreover, these IHL provisions apply only in international armed conflicts, while most contemporary armed conflicts are of a non-international character.

Some might argue that this is not problematic, because international human rights law protects the right to privacy and other rights that may be impacted by the use of biometrics in military operations. The application of international human rights law on the battlefield raises many of its own questions, however. These include the extent to which human rights obligations apply extraterritorially and the interrelationship between IHL and international human rights law. Both are hotly debated issues on which it is unlikely that consensus will be found any time soon.

All this suggests that it is important for governments and academics to pay more attention to the legal framework for the use of biometrics on the battlefield. One small part of such an effort would be to take a closer look at the applicable IHL rules. Do governments and academics share the interpretations of those rules discussed above? Do they consider that those interpretations impose overbroad limitations on the use of biometrics during armed conflict? If so, do they consider that we need new IHL rules to address biometrics specifically, or more broadly the use of data during armed conflict?

More generally, there is a need for increased clarity on the broader legal framework for the use of biometrics. As the pervasiveness of use on the battlefield intensifies, so too does the need for such clarity. Clarity is not only needed for those whose rights may be affected by it, but also for military personnel who require clear guidance.


Marten Zwanenburg is Professor of Military Law at the Faculty of Military Sciences of the Netherlands Defence Academy and a legal counsel with the International Law Division of the Ministry of Foreign Affairs of the Netherlands.

The views expressed are those of Professor Zwanenburg and do not necessarily represent those of the Ministry of Foreign Affairs or any other part of the government of the Netherlands.






[1] This is the definition used by NATO. See M. Lunan, New Doctrinal Concepts: Biometrics, 33 The Three Swords Magazine 37 (2018), 37.