The Blockade of Germany (1939–1945), also known as the Economic War, was carried out during World War II by the United Kingdom and France in order to restrict the supplies of minerals, metals, food and textiles needed by Nazi Germany - and later Fascist Italy - in order to sustain their war efforts. The economic war consisted mainly of a naval blockade which formed part of the wider Battle of the Atlantic, and included the preclusive buying of war materials from neutral countries to prevent their sale to the enemy.
There were four distinct phases of the blockade. The first period was from the beginning of European hostilities in September 1939 to the end of the "Phoney War," during which the Allies and Axis Powers both intercepted neutral merchant ships to seize deliveries en route to the enemy. The blockade was rendered less effective because the Axis could get crucial materials from the Soviet Union until June 1941, while harbours in Spain were used to import war materials for Germany. The second period began after the rapid Axis occupation of the majority of the European landmass which gave them control of major centres of industry and agriculture. The third period was from the end of 1941 after the beginning of hostilities between the United States and the Empire of Japan. The final period came after the tide of war finally turned against the Axis after heavy military defeats up to and after D-Day, which led to a gradual withdrawal from the occupied territories in the face of the overwhelming Allied military offensive.
At the beginning of the First World War in 1914, Great Britain used its powerful navy and its geographical location to dictate the movement of the world's commercial shipping. Britain dominated the North Sea, the Atlantic Ocean, the Mediterranean Sea and, due to its control of the Suez Canal with France, access into and out of the Indian Ocean for the allied ships, while their enemies were forced to go around Africa. The Ministry of Blockade published a comprehensive list of items that neutral commercial ships were not to transport to the Central Powers (Germany, Austria-Hungary, and the Ottoman Empire). This included food, weapons, gold and silver, flax, paper, silk, copra, minerals such as iron ore and animal hides used in the manufacture of shoes and boots. Because Britain and France together controlled 15 of the 20 refuelling points along the main shipping routes, they were able to threaten those who refused to comply, by the withdrawal of their bunker fuel control facilities.
In World War I, neutral ships were subject to being stopped to be searched for contraband. A large force, known as the Dover Patrol patrolled at one end of the North Sea while another, the Tenth Cruiser Squadron waited at the other. The Mediterranean Sea was effectively blocked at both ends and the dreadnought battleships of the Grand Fleet waited at Scapa Flow to sail out and meet any German offensive threat. Later in the war a large minefield, known as the Northern Barrage, was deployed between the Faroes and the coast of Norway to further restrict German ship movements.
Britain considered naval blockade to be a completely legitimate method of war, having previously deployed the strategy in the early nineteenth century to prevent Napoleon's fleet from leaving its harbours to attempt an invasion of England—Napoleon had also blockaded Britain. Germany in particular was heavily reliant on a wide range of foreign imports and suffered very badly from the blockade. Its own substantial fleet of modern warships was hemmed into its bases at Kiel and Wilhelmshaven by the Royal Navy and mostly forbidden by the leadership from venturing out. Germany carried out its own immensely effective counter-blockade during its war on Allied commerce (Handelskrieg), its U-boats sinking countless Allied merchant ships and by 1917 almost swung the war the way of the Central Powers. But because Britain found an answer to the U-boat by introducing the convoy system, the sustained Allied blockade led to the collapse and eventual defeat of the German armed forces by late 1918.
In 1933 Adolf Hitler became Chancellor of Germany and, following the remilitarization of the Rhineland, the Anschluss with Austria and the later occupation of Czechoslovakia, many people began to believe that a new 'Great War' was coming, and from late 1937 onwards Sir Frederick Leith-Ross, the British government's chief economics advisor, began to urge senior government figures to put thought into a plan to revive the blockade so that the Royal Navy – still the world's most powerful navy – would be ready to begin stopping shipments to Germany immediately once war was declared. Leigh-Ross had represented British interests abroad for many years, having embarked on a number of important overseas missions to countries including Italy, Germany, China and Russia, experience which gave him a very useful worldwide political perspective. His plan was to revive the original World War I blockade but to make it more streamlined, making better use of technology and Britain's vast overseas business and commercial network so that contacts in key trading locations such as New York, Rio de Janeiro, Tokyo, Rome or Buenos Aires could act as a vast information gathering system. Making use of tip-offs provided by a vast array of individuals such as bankers, merchant buyers, waterfront stevedores and ship operators doing their patriotic duty, the Navy could have priceless advance knowledge of which ships might be carrying contraband long before they reached port.
Initially the Prime Minister, Neville Chamberlain, was not keen on the idea and still hoped to avoid war, but following his appeasement of Hitler at Munich in September 1938, which was widely seen as a stopgap measure to buy time, he too began to realise the need for urgent preparations for war. During the last 12 months of peace, Britain and France carried out a vigorous buildup of their armed forces and weapons production. The long-awaited Spitfire fighter began to enter service, the first of the new naval vessels ordered under the 1936 emergency programme began to join the fleet, and the Air Ministry made the final touches to the Chain Home early warning network of radio direction-finding (later called radar) stations, to bring it up to full operational readiness.