Blockade A blockade is an effort to cut off food , supplies , war material or communications from a particular area by force , either in part or totally . A blockade should not be confused with an embargo or sanctions , which are legal barriers to trade , and is distinct from a siege in that a blockade is usually directed at an entire country or region , rather than a fortress or city . Most blockades historically took place at sea , with the blockading power seeking to cut off all maritime transport from and to the blockaded country ; although stopping all land transport to and from an area may also be considered a blockade . In the 20th century air power has also been used to enhance the effectiveness of the blockade by halting all air traffic within the blockaded air space . Close patrol of the hostile ports , in order to prevent naval forces from putting to sea , is also referred to as a blockade . When coastal cities or fortresses were besieged from the landward side , the besiegers would often blockade the seaward side as well . Most recently , blockades have sometimes included cutting off electronic communications by jamming radio signals and severing undersea cables . Types of blockade . Close , distant , and loose blockades . A " close " blockade entails placing warships within sight of the blockaded coast or port , to ensure the immediate interception of any ship entering or leaving . It is both the most effective and the most difficult form of blockade to implement . Difficulties arise because the blockading ships must remain continuously at sea , exposed to storms and hardship , usually far from any support , and vulnerable to sudden attack from the blockaded side , whose ships may stay safe in harbor until they choose to come out . In a " distant " blockade , the blockaders stay well away from the blockaded coast and try to intercept any ships going in or out . This may require more ships on station , but they can usually operate closer to their bases , and are at much less risk from enemy raids . This was almost impossible prior to the 16th century due to the nature of the ships used . A " loose " blockade is a close blockade where the blockading ships are withdrawn out of sight from the coast ( behind the horizon ) but no farther . The object of loose blockade is to lure the enemy into venturing out but to stay close enough to strike . British admiral Horatio Nelson applied a loose blockade at Cádiz in 1805 . The Franco - Spanish fleet under Pierre - Charles Villeneuve then came out , resulting in the Battle of Trafalgar . Pacific blockade . Until 1827 , blockades were always a part of a war . This changed when France , Russia and Britain came to the aid of the Greek rebels against Turkey . They blockaded the Turkish - occupied coast , which led to the battle of Navarino . War was never declared , however , so it is considered the first " pacific " — i . e . peaceful — blockade . The first truly pacific blockade , involving no shooting at all , was the British blockade of the Republic of New Granada in 1837 , established to compel New Granada to release an imprisoned British consul . Legal status . Since 1945 , the UN Security Council determines the legal status of blockades and by article 42 of the UN Charter , the Council can also apply blockades . According to the not ratified document San Remo Manual on International Law Applicable to Armed Conflicts at Sea , 12 June 1994 , a blockade is a legal method of warfare at sea but is governed by rules . The manual describes what can never be contraband . The blockading nation is free to select anything else as contraband in a list , which it must publish . The blockading nation typically establish a blockaded area of water , but any ship can be inspected as soon as it is established that it is attempting to break the blockade . This inspection can occur inside the blockaded area or in international waters , but never inside the territorial waters of a neutral nation . A neutral ship must obey a request to stop for inspection from the blockading nation . If the situation so demands , the blockading nation can request that the ship divert to a known place or harbour for inspection . If the ship does not stop , then the ship is subject to capture . If people aboard the ship resist capture , they can be lawfully attacked . Act of war . Whether or not a blockade was seen as lawful depended on the laws of the nations whose trade was influenced by the blockade . The Brazilian blockade of Río de la Plata in 1826 , for instance , was considered lawful according to British law but unlawful according to French and American law . The latter two countries announced they would actively defend their ships against Brazilian blockaders , while Britain was forced to steer for a peaceful solution between Brazil and Argentina . Blockade planning . Blockades depend on four general factors : Value of the thing to be blockaded . The value of the item being blockaded must warrant the need to blockade . For example , during the 1962 Cuban Missile Crisis , the items to be blockaded ( or " quarantined " to use the more legally neutral and politically neutral term selected by President John F . Kennedy ) were medium - range missiles , capable of delivering nuclear weapon ry , bound for Cuba . The need for the blockade was high because of the value of the missiles as a military threat against the United States . Blockading strength versus that of the opposing force . The strength of the blockading force must be equal to or greater in strength than the opposition . The blockade is only successful if the ' thing ' in question is prevented from reaching its receiver . Again , the Cuban blockade illustration shows that the United States put to sea a number of warships to inspect and blockade the waters around Cuba . This show of strength showed the United States Navy forces were much larger and stronger in the area than their Soviet Navy counterparts . Suitability of the terrain for the blockade . In the case of land blockades , choosing suitable terrain . Knowing where the force will be travelling will help the blockader choose where to blockade : for example , forcing a garrison between a high mountain pass in order to bottleneck the opposing force . Willpower to maintain the blockade . The success of a blockade is based almost entirely on the will of those who maintain it . The Cuban blockade is an example of maintaining willpower to block the missiles from reaching Cuba despite the risk of starting a nuclear Third World War . Blockade running . Blockade running is the practice of delivering cargo ( food , for example ) to a blockaded area . It has mainly been done by ships ( called blockade runner s ) across ports under naval blockade . Blockade runners were typically the fastest ships available and often lightly armed and armored . However , it is now also been done by aircraft , forming airbridges , such as over the Berlin blockade after World War II .