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.

The use of submarines in World War II and the development of submarine technology into the Cold War had implications for different fields of international law. This chapter addresses the peace negotiations and agreements that were adopted after World War II, which concerned the decommissioning (to varying degrees) of submarines and efforts to revise the Montreux Treaty. International law developments were sometimes slow, as evident in responses to violations of the law of naval warfare. Equally, the chapter highlights the rise of nuclear technology in relation to submarines and the modest advances in international agreements on nuclear tests. Despite the growing strategic importance of submarines in the Cold War, their explicit regulation in the 1958 conference and treaties on the law of the sea was scant. Instead, international laws relating to the passage of warships and military activities on the high seas generally impacted international laws regulating submarine operations.