page_title: Submarine warfare
section_title: World War I
hierarchical_section_title: Submarine warfare / World War I
caption_attribution_description: English: The Freedom of the Seas. From the Hun Point of View. British WWI propaganda poster, c. 1916, reaction to the sinking of RMS Lusitania in 1915
context_page_description: Submarine warfare is one of the four divisions of underwater warfare, the others being anti-submarine warfare, mine warfare and mine countermeasures.
  Submarine warfare consists primarily of diesel and nuclear submarines using torpedoes, missiles or nuclear weapons, as well as advanced sensing equipment, to attack other submarines, ships, or land targets. Submarines may also be used for reconnaissance and landing of special forces as well as deterrence. In some navies they may be used for task force screening. The effectiveness of submarine warfare partly depends on the anti-submarine warfare carried out in response.
context_section_description: Submarine warfare in World War I was primarily a fight between German and Austro-Hungarian U-boats and supply convoys bound for the United Kingdom, France, and Russia. British and Allied submarines conducted widespread operations in the Baltic, North, Mediterranean and Black Seas along with the Atlantic Ocean. Only a few actions occurred outside the wider European-Atlantic theatre. German submarine attacks on Allied merchant ships, especially the sinking of Lusitania, turned American public opinion against the Central Powers. The U.S. demanded it stop, and Germany did so.  Admiral Henning von Holtzendorff (1853–1919), chief of the admiralty staff, argued successfully in January 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. and played a large role in the United States entering the war in April 1917.
  All participants were supposed to abide by the Hague Conventions of 1899 and 1907, but this was found to be impracticable for submarines. The German government maintained the British naval blockade was illegal under international law. Initially, German submarines did attempt to comply with the prize rules, but later switched to unrestricted submarine warfare following the British introduction of Q-ships with concealed deck guns. American diplomatic pressure forced the Germans to stop this for a while, but in January 1917 Germany declared a war zone around the British Isles and sank up to a quarter of shipping entering it, until escorted convoys were introduced.
   The sinking of HMS Pathfinder was the first combat victory of a modern submarine, and the exploits of SM U-9, which sank three British cruisers in under an hour, established the submarine as an important new component of naval warfare.
  German submarines were used to lay naval mines and to attack iron ore shipping in the Baltic. The British submarine flotilla in the Baltic operated in support of the Russians until the Treaty of Brest-Litovsk. During the war, the British invested efforts into developing a submarine that could operate in conjunction with a battleship fleet – the "Fleet Submarine".  To achieve the necessary 20 knots (37 km/h) (surfaced) the K-class submarines were steam powered. In practice, the K class were a constant problem and could not operate effectively with a fleet.
caption: British WWI propaganda poster
exif: {}