In assessing international law governing submarine warfare, we consider how peacetime rules from the law of the sea apply in an armed conflict and focus on the law of neutrality and the law of armed conflict (international humanitarian law). The allocation of rights and duties within different maritime zones continues, albeit with some modifications, during an armed conflict. Most notably, the law of neutrality establishes how those rights and duties change depending on a State’s status as a belligerent or neutral. The use of submarines during armed conflict is also governed by the law of naval warfare and they are largely subject to the same rules that restrict surface warships in relation to targeting, as well as the means and methods of warfare. While submarines are predominantly governed as warships, we note how operational limitations of submarines may affect the interpretation of some rules.