Merging man and machine: A legal assessment of brain–computer interfaces in armed conflict

Abstract Imagine a future where man and machine become one on the battlefield, where soldiers direct weapon systems through a neural implant. Research advances on brain–computer interfaces (BCIs) may eventually allow such control of arms at the speed of thought. This article sketches two modes of BCI-controlled weapon systems. In Mode A (active BCI), the soldier opens fire by actively imagining that he is pushing a button with his hand. By contrast, Mode B (reactive BCI) captures neural signals evoked instantly after having spotted a target, before the operator becomes consciously aware of it. If he deems the target lawful, the brain signal is translated into a command to fire. Arguing that such man–machine collaboration transforms the operating soldier into a means of warfare, this article conducts a weapon review in line with Article 36 of Additional Protocol I (AP I) to answer the question of whether BCIs can be lawfully used to control weapons in international armed conflict. Consequently, the two set-ups are reviewed on their compliance with the customary targeting principles of international humanitarian law. Since Mode B casts doubt on the amount of control that the soldier retains over his targeting decision, the concept of meaningful human control is transposed from the debate on lethal autonomous weapon systems and applied to BCIs. It is found that reactive BCIs cannot be meaningfully controlled and thus violate the principles of distinction and proportionality. Hence, reactive BCIs are unlawful under Article 36 of AP I.