<P> 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 (also known as "cruiser rules"). Prize rules call for submarines to surface and search merchantmen and place crews in "a place of safety" (for which lifeboats did not qualify, except under particular circumstances) before sinking them, unless the ship showed "persistent refusal to stop...or active resistance to visit or search". The Germans disregarded the law during the First World War following the British introduction of Q - ships with concealed deck guns, and in the most dramatic episode sank Lusitania in 1915 in a few minutes because they believed it 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 . </P> <P> 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 (or raiders) 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 . </P> <P> There have been four major campaigns of unrestricted submarine warfare: </P>

What was the germany's policy of unrestricted submarine warfare