thumb|right|275px|[[Admiral Horatio Nelson's English fleet blockaded
Toulon, France in 1810-1814.]]
thumb|right|275px|[[C47s unloading at
Tempelhof Airport in
Berlin, part of the airlift of supplies which broke the
Soviet Union's 1948
land blockade of West Berlin]]
A
blockade is an effort to cut off food, supplies, war matériel or communications from a particular area by force, either in part or
in toto. 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. Also, a blockade 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.
Close patrol of a hostile port, in order to prevent naval forces from putting to sea, is also referred to as a blockade. When a coastal city or fortress was besieged from the landward side, the besiegers would often blockade the seaward side as well. In the twentieth century, blockades sometimes included stopping all air traffic within the blockaded area. Most recently, blockades have sometimes included cutting off electronic communications by
jamming radio signals and severing undersea cables.
The
International Criminal Court plans to include blockades against coasts and ports in its list of
acts of war in 2009.
Types of blockade
thumb|left|225px|In World War II, [[Nazi Germany|German U boats attempted to stop ships carrying food, supplies and matériel from reaching the United Kingdom, an example of a
distant 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, vulnerable to sudden attack from the blockaded side, whose ships may stay safe in harbor till they choose to come out and usually far from any support.
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.
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, while staying close enough to strike.
British
admiral Horatio Nelson applied a loose blockade at
Cádiz in 1805. The Franco-Spanish fleet under
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
thumb|right|215px|[[John F. Kennedy|President Kennedy and his advisors discuss the
Cuban Missile Crisis. Part of the US response to
Soviet missiles being placed in
Cuba was a naval blockade of the island.]]
Act of war
A blockade is defined by the
Encyclopedia Britannica as an "an act of war by which a belligerent prevents access to or departure from a defined part of the enemy’s coasts".
Governing laws
Whether or not a blockade was seen as lawful depended on the national 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.
Blockades were first defined in
international law at the
Congress of Paris in 1856. One of the agreed rules was that a blockade had to be effective in order to be lawful. This banned so-called "paper" blockades – blockades that were declared to the blockaded nation, but were not actively enforced, allowing the blockading party to seize the cargo of neutral states trading with blockaded harbors. At the
Declaration of London in 1909 another attempt was made to further protect the rights of neutral traders. The treaty was only ratified by a few nations, preventing any application of the agreements. Parts of it were, however, applied during blockades in
World War I.
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.
Blockade planning
thumb|right|325px|A Northern cartoonist ridicules the [[Union (American Civil War)|Union's initial attempts to blockade ports of the
Confederacy in the
American Civil War.]]
Blockades depend on four general factors:
- The value of the thing to be blockaded
- The blockading strength versus that of the opposing force
- The suitability of the terrain for the blockade
- The willpower to maintain the blockade
First: 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- and politically-neutral term selected by
President John F. Kennedy) were medium-range missiles, capable of delivering
nuclear weaponry, 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.
Second: 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
U.S. Navy forces were much larger and stronger in the area than their
Soviet Navy counterparts.
Third: 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.
Fourth: the willpower to maintain a blockade. The success of a blockade is based almost entirely on the will of the people 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 worldwide
nuclear 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 runners) across ports under naval blockade. Blockade runners were typically the fastest ships available and often lightly armed and armored. However, in the modern age, it has also been done by aircraft, forming
airbridges, such as over the
Berlin blockade after
World War II.
Historical blockades
thumb|right|350px|On the blockade off [[San Juan, Puerto Rico in 1898 during the
Spanish American War]]
- During the Peloponnesian War (431 BC–404 BCE), Spartan forces surrounded Athens on land. Athens withstood the landward attack, and subsisted on food imported by ship. After the battle of Aegospotami, Sparta also blockaded Athens by sea, and Athens surrendered.
- When Alexander the Great sought to take the city of Tyre in 332 BCE, he first blockaded the city for several months.
- 1915 to 1918 Ottoman blockade of Lebanon.
