During its engagement in Afghanistan, the US military seriously tried to mitigate the risk of civilian casualties from airstrikes only when called for by changes in military doctrine emphasizing the need to gain the support of the population. Consistent efforts by external political and humanitarian actors to reduce casualties by demanding more transparency and clearer lines of accountability for ‘collateral damage’ had little immediate, observable effect. The case study underlines the contingent nature of progress towards protecting civilians in armed conflict even when a military institution formally accepts the principles of customary international humanitarian law, but concludes that, faute de mieux, strategies to enhance protection through greater accountability and attention to the kind of military ordinance used remain central.