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.