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Unpublished Paper
Applying Jus in Bello Proportionality to Drone Warfare
ExpressO (2013)
  • David J. Akerson, University of Denver

This article applies the international humanitarian law (IHL) principle of proportionality to the use of unmanned aerial vehicles (UAVs), commonly referred to as drones,[1] by the United States military forces (US Military) and the United States Central Intelligence Agency (CIA) in its armed conflicts in Iraq and Afghanistan and the “war on terror” in places such as Pakistan, Yemen, Somalia and Mali.[2] Iraq and Afghanistan at some point were more conventional armed conflicts that yielded to occupations with a continuing conflict against irregular insurgents. Pakistan, Yemen, Somalia and Mali fall into the so-called “targeted killings” genre, defined as “premeditated attacks of lethal force employed by states in times of peace or during armed conflict to eliminate specific individuals outside their custody.”[3]

Both of these types of situations are emblematic of what we can expect future military engagements to resemble: asymmetrical conflicts involving the use of highly sophisticated UAVs deployed by professional armed forces, remotely piloted from outside the theatre of conflict, attacking irregular militants who operate in or near civilian populations. For the purposes of this article, collectively this tactic will be termed “UAV warfare.”

In armed conflicts, the IHL proportionality rule (IHL Proportionality) prohibits an attack when the anticipated military advantage of the attack is excessive compared to the expected civilian harm. UAV warfare to date has resulted in a significant number of civilian casualties, leading some to conclude that the tactic is inherently disproportionate. These conclusions are often problematic. First, they commonly confuse or conflate IHL proportionality with similar concepts found in international jus ad bellum and human rights law or a colloquial sense of the term. Second, they nearly always issue summary conclusions of its effect with little explanation about the actual operation of the rule.

In this article, I examine IHL proportionality in detail and as applied in the context of the unique aspects of UAV warfare. Existing cases and commentary regularly assume that proportionality is a one-sized-fits-all rule, whether the impugned attacker is a four-star general or a lowly platoon commander. This Article asserts that proportionality requires different applications in the cases of high-ranking and low-ranking belligerents. The Article also emphasizes how courts and commentators frequently fall into the trap of retrospectively applying casualty statistics to assess the proportionality of an attack, rather than using those statistics to inform the reasonableness of the attacker’s a prioriassessment.

[1] There are hundreds of kinds of unmanned aerial vehicles. This article focuses on two that have the capability to deploy lethal force – Predator and Reapers drones – and have been used extensively in this capacity. This Article will use the terms UAVs and drones interchangeably to refer exclusively to Predator and Reaper drones.

[2] Jonathan Masters, Targeted Killings, Council on Foreign Relations (May 23, 2013), available at

[3] Philip Alston, UN: Report of the Special Rapporteur on Extrajudicial Summary, or Arbitrary Executions, Council on Foreign Relations (May 28, 2010),

  • Proportionality,
  • Drones,
  • UAVs,
  • Humanitarian Law,
  • Law of Armed Conflict
Publication Date
November 13, 2013
Citation Information
David J. Akerson. "Applying Jus in Bello Proportionality to Drone Warfare" ExpressO (2013)
Available at: