<Ol> <Li> 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 U-20 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 . It was also a casus belli for the entry of Brazil into the war in 1917 . </Li> <Li> The Battle of the Atlantic during World War II . Between 1939 and 1945, it was waged between Germany and the Allies and from 1940 to 1943 between Italy and the Allies . </Li> <Li> 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 . </Li> <Li> The Pacific War during World War II, between 1941 and 1945, waged by the United States against Japan . </Li> </Ol> <Li> 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 U-20 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 . It was also a casus belli for the entry of Brazil into the war in 1917 . </Li> <Li> The Battle of the Atlantic during World War II . Between 1939 and 1945, it was waged between Germany and the Allies and from 1940 to 1943 between Italy and the Allies . </Li> <Li> 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 . </Li>

How did the german policy of unrestricted submarine warfare affect the united states