Between the mid-fifteenth and mid-seventeenth centuries, norms on maritime warfare by both private and public actors developed through the intensification of maritime trade networks, European colonial and commercial expansion in other continents, the growing ascendancy of the sovereign state, and the emergence of a distinctive legal scholarship on topics of the law of nations. Although even among European political actors, there was still no general consensus on precise and binding norms governing maritime warfare, the building stones of a normative framework were gradually established which would be integrated from the later seventeenth century onwards into a more consistent body of international law. Prize courts played a crucial role in promoting the principles of such a legal framework, as did state practice on key issues such as blockade, contraband and neutrality.

This chapter offers a discussion on the laws of war, or jus in bello, as the previous one. However, it provides an exclusive focus on maritime warfare. Old Regime Europe was marked by the expansion of permanent state battlefleets and the strengthening of naval administrations. At the same time, a complementarity between public and private forms of maritime warfare, notably privateering, persisted as one of the defining aspects of naval warfare. The chapter deals with the specificity of waging war at sea and related legal issues. It draws both from state-military practice and from the specialised legal literature that started to appear at the time. Subjects which are covered include the main rules of naval warfare, privateering, the treatment of prisoners of war, the bombardment of coastal cities, prize law and the role of admiralty courts. Particular attention is devoted to the issue of maritime neutrality. Indeed, the recurrent tension between the respective rights and duties of neutrals and belligerents assumed great relevance in this period, being often dealt with in international treaties and legal scholars’ treatises.

By comparison with the continental powers, Britain had no more than a medium-sized army, but the largest navy in Europe.  This chapter seeks to explore the bases of Britain’s naval strength, going back to the seventeenth-century Navigation Acts, and then to consider how that strength was deployed in the war against Napoleon.  It argues that the Royal Navy, despite the limited impact it might be thought that it could have on land warfare, played an important part in the final defeat of Napoleon.