While most law on the conduct of hostilities has been heavily scrutinized in recent years, the law dealing with armed conflict at sea has been largely ignored. This is not surprising. There have been few naval conflicts since 1945, and those that have occurred have been limited in scale; none has involved combat between major maritime powers. Nevertheless, navies have tripled in number since then, and today there are growing tensions between significant naval powers. There is a risk of conflict at sea. Conditions have changed since 1945, but the law has not developed in that time. Elements of it, especially that regulating economic warfare at sea, seem outdated and it is not clear that the law is well placed to regulate socalled “hybrid” warfare at sea. It seems timely to review the law, to confirm that which is appropriate and to develop that which is not. Perhaps a new edition of the San Remo Manual would be timely.