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.