World War I: Germany announces that its U-boats will resume unrestricted submarine warfare after a two-year hiatus.
The U-boat Campaign from 1914 to 1918 was the World War I naval campaign fought by German U-boats against the trade routes of the Allies. It took place largely in the seas around the British Isles and in the Mediterranean.
The German Empire relied on imports for food and domestic food production (especially fertilizer) and the United Kingdom relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade one another. The British had the Royal Navy which was superior in numbers and could operate on most of the world's oceans because of the British Empire, whereas the Imperial German Navy surface fleet was mainly restricted to the German Bight, and used commerce raiders and unrestricted submarine warfare to operate elsewhere.In the course of events in the Atlantic alone, German U-boats sank almost 5,000 ships with nearly 13 million gross register tonnage, losing 178 boats and about 5,000 men in combat. Other naval theatres saw U-boats operating in both the Far East and South East Asia, the Indian Ocean and the Mediterranean and North Seas.
U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role (commerce raiding) and enforcing a naval blockade against enemy shipping. The primary targets of the U-boat campaigns in both wars were the merchant convoys bringing supplies from Canada and other parts of the British Empire, and from the United States, to the United Kingdom and (during the Second World War) to the Soviet Union and the Allied territories in the Mediterranean. German submarines also destroyed Brazilian merchant ships during World War II, causing Brazil to declare war on both Germany and Italy on 22 August 1942.The term is an anglicised version of the German word U-Boot [ˈuːboːt] (listen), a shortening of Unterseeboot ('under-sea-boat'), though the German term refers to any submarine. Austro-Hungarian Navy submarines were also known as U-boats.