Abstract

The ethical Principle of Proportionality requires combatants not to cause collateral harm excessive in comparison to the anticipated military advantage of an attack. This principle is considered a major (and perhaps insurmountable) obstacle to ethical use of autonomous weapon systems (AWS). This article reviews three possible solutions to the problem of achieving Proportionality compliance in AWS. In doing so, I describe and discuss the three components Proportionality judgments, namely collateral damage estimation, assessment of anticipated military advantage, and judgment of “excessiveness”. Some possible approaches to Proportionality compliance are then presented, such as restricting AWS operations to environments lacking civilian presence, using AWS in targeted strikes in which proportionality judgments are pre-made by human commanders, and a ‘price tag’ approach of pre-assigning acceptable collateral damage values to military hardware in conventional attritional warfare. The article argues that application of these three compliance methods would result in AWS’ achieving acceptable Proportionality compliance levels in many combat environments and scenarios, allowing AWS to perform most key tasks in conventional warfare.