World War II: The United Kingdom and France begin a naval blockade of Germany that lasts until the end of the war. This also marks the beginning of the Battle of the Atlantic.

The Blockade of Germany (1939–1945), also known as the Economic War, involved operations carried out during World War II by the British Empire and by France in order to restrict the supplies of minerals, fuel, metals, food and textiles needed by Nazi Germany – and later by 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, but also included the bombing of economically important targets and the preclusive buying of war materials from neutral countries in order to prevent their sale to the Axis powers.

• The first period, from the beginning of European hostilities in September 1939 to the end of the "Phoney War", saw both the Allies and the Axis powers intercepting neutral merchant ships to seize deliveries en route to their respective enemies. Naval blockade at this time proved less than effective because the Axis could get crucial materials from the Soviet Union until June 1941, while Berlin used harbours in Spain to import war materials into Germany.
• The second period began after the rapid Axis occupation of the majority of the European landmass in 1940–1941, resulting in Axis control of major centres of industry and agriculture.
• The third period started in December 1941 after the attack on Pearl Harbor by the Imperial Japanese Navy Air Service brought the U.S. officially into the European war.
• The final period came after the tide of war finally turned against the Axis after heavy military defeats up to and after D-Day in June 1944, which led to gradual Axis withdrawals from the occupied territories in the face of the overwhelming Allied military offensives.

The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counterblockade. The campaign peaked from mid-1940 to the end of 1943.