Unrestricted submarine warfare is a type of naval warfare in which submarines sink vessels such as freighters and tankers without warning, as opposed to attacks per prize rules. Prize rules call for submarines to surface and search merchantmen and place crews in "a place of safety" before sinking them, unless the ship showed "persistent refusal to stop... or active resistance to visit or search". During the First World War, the British introduced Q-ships with concealed deck guns, and armed many merchantmen, leading the Germans to ignore the prize rules; in the most dramatic episode they sank in 1915 in a few minutes because she was carrying war munitions. The U.S. demanded it stop, and Germany did so. Admiral Henning von Holtzendorff, chief of the Admiralty staff, argued successfully in early 1917 to resume the attacks and thus starve the British. The German high command realized the resumption of unrestricted submarine warfare meant war with the United States but calculated that American mobilization would be too slow to stop a German victory on the Western Front. Following Germany's resumption of unrestricted submarine warfare on February 1, 1917, countries tried to limit or even abolish submarines. Instead, the Declaration of London required submarines to abide by prize rules. These regulations did not prohibit arming merchantmen but having them report contact with submarines made them de facto naval auxiliaries and removed the protection of the prize rules. This rendered the restrictions on submarines effectively useless. While such tactics increase the combat effectiveness of the submarine and improve its chances of survival, some regard them as a breach of the rules of war, especially when employed against neutral vessels in a war zone. In 1922 the United States, Britain, Japan, France and Italy signed a Washington Treaty on Poison Gas and Submarines, to so restrict the use of submarines as to make them useless as commerce raiders. France did not ratify, so the treaty did not go into effect.
Instances
There have been four major campaigns of unrestricted submarine warfare, one in World War I and three in World War II:
The U-boat campaign of World War I, waged intermittently by Germany between 1915 and 1918 against Britain and her allies. One of the most famous acts was on May 7, 1915 when U-boat deliberately torpedoed the British Cunard luxury liner RMS Lusitania. Germany's resumption of unrestricted submarine warfare in February 1917, together with the Zimmermann Telegram, brought the United States into the war on the British side.
The Battle of the Atlantic during World War II. Between 1939 and 1945, it was waged between Germany and the Allies and also from 1940 to 1943 between Italy and the Allies.
The Baltic Sea Campaigns on the Eastern Front, during World War II between 1941 and 1945, especially from 1942. Waged by Germany and the USSR against each other, primarily in the Baltic Sea.
The Pacific War during World War II, between 1941 and 1945, waged by the United States against Japan.
The four cases were attempts to impose a naval blockade on countries, especially those heavily dependent on merchant shipping to supply their war industries and feed their populations, even though the countries waging the unrestricted submarine warfare were unable to institute a conventional naval blockade.
