7.7 BLOCKADE
7.7.1 General. Blockade is a belligerent operation to prevent vessels and/or aircraft of all nations, enemy as well as neutral, from entering or exiting specified ports, airfields, or coastal areas belonging to, occupied by, or under the control of an enemy nation. A belligerent's purpose in establishing a blockade is to deny the enemy the use of enemy and neutral vessels or aircraft to transport personnel and goods to or from enemy territory. While the belligerent right of visit and search is designed to interdict the flow of contraband goods, the belligerent right of blockade is intended to prevent vessels and aircraft, regardless of their cargo, from crossing an established and publicized cordon separating the enemy from international waters and/or airspace.
7.7.2 Traditional Rules. In order to be valid under the traditional rules of international law, a blockade must conform to the following criteria.
7.7.2.1 Establishment. A blockade must be established by the government of the belligerent nation. This is usually accomplished by a declaration of the belligerent government or by the commander of the blockading force acting on behalf of his government. The declaration should include, as a minimum, the date the blockade is to begin, its geographic limits, and the grace period granted neutral vessels and aircraft to leave the area to be blockaded.
7.7.2.2 Notification. It is customary for the belligerent nation establishing the blockade to notify all affected nations of its imposition. Because knowledge of the existence of a blockade is an essential element of the offenses of breach and attempted breach of blockade (see paragraph 7.7.4), neutral vessels and aircraft are always entitled to notification. The commander of the blockading forces will usually also notify local authorities in the blockaded area. The form of the notification is not material so long as it is effective.
7.7.2.3 Effectiveness. In order to be valid, a blockade must be effective. To be effective, it must be maintained by a surface, air, or subsurface force or other mechanism that is sufficient to render ingress or egress of the blockaded area dangerous. The requirement of effectiveness does not preclude temporary absence of the blockading force, if such absence is due to stress of weather or to some other reason connected with the blockade (e.g., pursuit of a blockade runner). Nor does effectiveness require that every possible avenue of approach to the blockaded area be covered.
7.7.2.4 Impartiality. A blockade must be applied impartially to the vessels and aircraft of all nations. Discrimination by the blockading belligerent in favor of or against the vessels and aircraft of particular nations, including those of its own or those of an allied nation, renders the blockade legally invalid.
7.7.2.5 Limitations. A blockade must not bar access to or departure from neutral ports and coasts. Neutral nations retain the right to engage in neutral commerce that does not involve trade or communications originating in or destined for the blockaded area.
7.7.3 Special Entry and Exit Authorization. Although neutral warships and military aircraft enjoy no positive right of access to blockaded areas, the belligerent imposing the blockade may authorize their entry and exit. Such special authorization may be made subject to such conditions as the blockading force considers to be necessary and expedient. Neutral vessels and aircraft in evident distress should be authorized entry into a blockaded area, and subsequently authorized to depart, under conditions prescribed by the officer in command of the blockading force or responsible for maintenance of the blockading instrumentality (e.g., mines). Similarly, neutral vessels and aircraft engaged in the carriage of qualifying relief supplies for the civilian population and the sick and wounded should be authorized to pass through the blockade cordon.
7.7.4 Breach and Attempted Breach of Blockade. Breach of blockade is the passage of a vessel or aircraft through a blockade without special entry or exit authorization from the blockading belligerent. Attempted breach of blockade occurs from the time a vessel or aircraft leaves a port or airfield with the intention of evading the blockade, and for vessels exiting the blockaded area, continues until the voyage is completed. Knowledge of the existence of the blockade is essential to the offenses of breach of blockade and attempted breach of blockade. Knowledge may be presumed once a blockade has been declared and appropriate notification provided to affected governments. It is immaterial that the vessel or aircraft is at the time of interception bound for neutral territory, if its ultimate destination is the blockaded area. There is a presumption of attempted breach of blockade where vessels or aircraft are bound for a neutral port or airfield serving as a point of transit to the blockaded area. Capture of such vessels is discussed in paragraph 7.10.
7.7.5 Contemporary Practice. The traditional rules of blockade, as set out above, are for the most part customary in nature, having derived their definitive form through the practice of maritime powers during the nineteenth century. The rules reflect a balance between the right of a belligerent possessing effective command of the sea to close enemy ports and coastlines to international commerce, and the right of neutral nations to carry out neutral commerce with the least possible interference from belligerent forces. The law of blockade is, therefore, premised on a system of controls designed to effect only a limited interference with neutral trade. This was traditionally accomplished by a relatively "close-in" cordon of surface warships stationed in the immediate vicinity of the blockaded area.
The increasing emphasis in modern warfare on seeking to isolate completely the enemy from outside assistance and resources by targeting enemy merchant vessels as well as warships, and on interdicting all neutral commerce with the enemy, is not furthered substantially by blockades established in strict conformity with the traditional rules. In World Wars I and II, belligerents of both sides resorted to methods which, although frequently referred to as measures of blockade, cannot be reconciled with the traditional concept of the close-in blockade. The so-called long-distance blockade of both World Wars departed materially from those traditional rules and were justified instead upon the belligerent right of reprisal against illegal acts of warfare on the part of the enemy. Moreover, recent developments in weapons systems and platforms, particularly submarines, supersonic aircraft, and cruise missiles, have rendered the in-shore blockade exceedingly difficult, if not impossible, to maintain during anything other than a local or limited armed conflict.
Notwithstanding this trend in belligerent practices (during general war) away from the establishment of blockades that conform to the traditional rules, blockade continues to be a useful means to regulate the competing interests of belligerents and neutrals in more limited armed conflict. The experience of the United States during the Vietnam Conflict provides a case in point. The mining of Haiphong and other North Vietnamese ports, accomplished by the emplacement of mines, was undertaken in conformity with traditional criteria of establishment, notification, effectiveness, limitation, and impartiality, although at the time the mining took place the term "blockade" was not used.
