This article discusses the potential influence of the existence of an underlying armed conflict in Gaza on the applicability and application of jus ad bellum. It rejects the Israeli ‘displacement’ approach whereby jus ad bellum does not play a role during an ongoing armed conflict as it finds no support in the sources of international law, in particular state practice. The article then provides possible explanations for the Israeli reliance on ‘displacement’ regardless of its shaky foundations: namely, the preference to provide overall justification for the operation, to avoid difficult political topics, and to allow Israel freedom of action in other arenas (such as Lebanon and Syria). Regardless of such findings, the article acknowledges that jus ad bellum faces challenges to its application during hostilities. It analyses the right of self-defence, as Israel has relied on such right to justify its use of force in Gaza, addressing relatively briefly jus ad bellum necessity while focusing on the various approaches to jus ad bellum proportionality, and the differences between such approaches when it comes to the legality of the use of force in self-defence in Gaza. Ultimately, the article argues that states must provide clear pronouncements on this issue to prevent the adoption of an overly permissive approach to the regulation of jus ad bellum during hostilities.