BY THE EARLY NINETEENTH CENTURY maritime blockade was the offensive arm of economic warfare, used against an enemy in conjunction with the convoy protection of a nation's own overseas trade. The term ‘offensive blockade’ was used to describe the interception of an enemy's merchant, transport or naval vessels, usually on their entering or leaving harbour. Defensive economic warfare involved the gathering of merchant vessels to sail as convoys under the armed protection of as many warships as could be spared. Belligerents with sufficient naval means were increasingly expected to impose a policy of ‘stop and search’ on all vessels found in specified areas, and those carrying goods ‘interdicted’ by proclamation as ‘contraband’ were at best turned back or, otherwise, detained. Crews and cargoes thought likely to benefit an enemy were either subject to an enforced sale or, subject to law, confiscated. At the beginning of each European war legislation was needed to legitimise what otherwise would have constituted piracy, a practice almost universally condemned but nonetheless still carried out in some parts of the world.