One of the key functions of Canadian armed forces in the Gulf War was the naval enforcement of the trade embargo on Iraq. Such action has been considered a critical component of international affairs for centuries. In this study Nicholas Tracy considers the motives for attack on maritime trade, and assesses its strategic utility. He begins with a discussion of the strategic purposes of this kind of activity, and goes on to consider its applications in the twentieth century: during the First World War, through the Belligerents' Rights dispute and the rise of the 'New Mercantilism,' in trade control between the wars, and on several fronts in the Second World War. Finally he examines instances of naval blockade and attack on shipping since 1945, and offers a number of conclusions about its effectiveness.