<P> In February 1915, a submarine U-6 (Lepsius) was rammed and both periscopes were destroyed off Beachy Head by the collier SS Thordis commanded by Captain John Bell RNR after firing a torpedo . On 7 May 1915, SM U-20 sank the liner RMS Lusitania . The sinking claimed 1,198 lives, 128 of them American civilians, and the attack of this unarmed civilian ship deeply shocked the Allies . According to the ship's manifest, Lusitania was carrying military cargo, though none of this information was relayed to the citizens of Britain and the United States who thought that the ship contained no ammunition or military weaponry whatsoever and it was an act of brutal murder . Munitions that it carried were thousands of crates full of ammunition for rifles, 3 - inch artillery shells, and also various other standard ammunition used by infantry . The sinking of the Lusitania was widely used as propaganda against the German Empire and caused greater support for the war effort . A widespread reaction in the U.S was not seen until the sinking of the ferry SS Sussex . The sinking occurred in 1915 and the United States entered the war in 1917 . </P> <P> The initial U.S. response was to threaten to sever diplomatic ties, which persuaded the Germans to issue the Sussex pledge that reimposed restrictions on U-boat activity . The U.S. reiterated its objections to German submarine warfare whenever U.S. civilians died as a result of German attacks, which prompted the Germans to fully reapply prize rules . This, however, removed the effectiveness of the U-boat fleet, and the Germans consequently sought a decisive surface action, a strategy that culminated in the Battle of Jutland . </P> <P> Although the Germans claimed victory at Jutland, the British Grand Fleet remained in control at sea . It was necessary to return to effective anticommerce warfare by U-boats . Vice-Admiral Reinhard Scheer, Commander in Chief of the High Seas Fleet, pressed for all - out U-boat war, convinced that a high rate of shipping losses would force Britain to seek an early peace before the United States could react effectively . </P> <P> The renewed German campaign was effective, sinking 1.4 million tons of shipping between October 1916 and January 1917 . Despite this, the political situation demanded even greater pressure, and on 31 January 1917, Germany announced that its U-boats would engage in unrestricted submarine warfare beginning 1 February . On 17 March, German submarines sank three American merchant vessels, and the U.S. declared war on Germany in April 1917 . </P>

Who invented the u boat in world war 1