A blockade, historically, is the use of a nation’s (or alliance of nations’) naval forces to prevent ships from entering or leaving an enemy’s ports, coasts or waters.
Blockades have been for military or commercial ends, though often it has been a combination of both. In either there is the necessity for the blockading power to have the greater force in the area being blockaded, especially if is a “close” blockade; that is of a particular port or coastline where the blockading fleets can keep permanent watch. An “open blockade” is one where the general lines of trade across oceans are attacked. A prime example of an open blockade was the Battle of the Atlantic during World War II where U-boats were used in an attempt to cut off the supply of food, fuel and materials to the British Isles. There is a fine line here between a blockade and what might be called “commerce raiding.”
The concept is relatively recent and could only be applied when ships had reached a high level of seaworthiness and the lines of supply and communications improved accordingly. Once a nation could keep a fleet close to the enemy’s coast for a long enough period to cause economic or material hardship the blockade as a strategy came into being. During the Anglo-Dutch Wars of the mid-seventeenth century the development of the ship of the line, the parallel development of a system of communications by flags and the creation of a naval supply system under Samuel Pepys led to the British being able to blockade the Netherlands coast at great economic cost to the Dutch.
The Royal Navy's blockade of the French Atlantic and Mediterranean coasts – especially of its naval dockyards - in 1759 during the Seven Years' War effectively caused French preparations for an invasion of Britain to grind to a halt. Men and material were being collected on the south coast of Brittany where hundreds of barges were being prepared as troop carriers. The main French fleets – those that weren’t being kept busy in the Caribbean and off India – were being blockaded in Brest at the westernmost part of France and in the Mediterranean naval dockyard at Toulon. It was the French “escape”, first from Toulon in August of that year whilst the English were making repairs at Gibraltar and then from Brest in atrocious weather in November that brought about the two decisive naval battles of the war. The Battle of Lagos and the Battle of Quiberon Bay effectively ended any chance of a French invasion.
During the Napoleonic Wars the whole thing happened again. Napoleon wanted to invade Britain and began preparations. The Royal Navy blockaded the French and Spanish coasts for months on end disrupting all coastal trade and making it impossible for all the “ingredients” necessary for the invasion to be brought together in one place. When Nelson’s fleet met the Franco/Spanish fleet off Trafalgar, there was one great similarity to 1759; a hardened experienced, well-drilled British fleet was meeting a fleet soft and unsure of itself from months cooped up in port.
Napoleon countered with a blockade of his own, ordering that all British ships entering continental Europe to be seized – the “Continental System”. The British increased their blockade to all of Europe. Napoleon was forced to back down when the economy started to suffer.
British attempts at blockading the Americans during the American Revolution were made difficult by the intervention of the French and in the War of 1812 Britain was already blockading the whole Atlantic coast of Europe and had not the resources for a close blockade.
Maritime blockades continued through the nineteenth century. Specialist blockades occurred, particularly in fighting the slave trade. The Union began a blockade of Confederate ports immediately after the start of hostilities in 1861. There has been debate whether the blockade was more effective in its denial of imports of manufactured items to the South or in the disruption to its export of cotton. Whilst considered extremely effective it is not known whether it shortened the war. In the 1904-1905 Russo-Chinese War, the Japanese blockaded the Russian Eastern fleet in Port Arthur harbour where it was destroyed after a land siege. This may have been the end of the “close blockade” as the development of longer range weapons, radio and fast patrol vessels negated the need to be “in sight” of the targeted coast and it was officially abandoned by the British in 1912. Mines became an element of blockades during World War I. The laying of mines in particular areas with proclaimed freeways made it easier to intercept commercial vessels plying certain routes in the north-eastern Atlantic. The Allied blockade became so effective that only 3 ships supplying Germany reached ports under German control in the last half of 1916.
Blockades were not as successful during the Second World War but still played a part in the commercial isolation of the Axis nations. The United Nations blockaded North Korea during the Korean War however it was of limited value because of the land contact with China.
The last full naval blockade occurred during the Cuban Missile Crisis of 1962 when the U.S. Navy completely blockaded Cuba. Since then naval blockades have become part of embargoes or sanctions called against certain nations – Iraq, the former Yugoslavia etc.,