The Germans had a policy of unrestricted submarine warfare, and this caused them to attack any ship within designated areas. On May 7, 1915, a German U-boat sunk a British ocean liner heading to Liverpool, England from New York. This ship was the RMS Lusitania, and there were about 1,900 passengers. Out of all of those people, 1,100 died, and 120 of the dead were American. Before the ship left the harbor, there was a warning sent to America from Germany that they would attack all ships in certain places ships, and Germans had a history of attacking neutral ships. The captain of the Lusitania saw the warning, but departed anyway, fully aware of the threat. A U-boat fired a torpedo into the ship, and it triggered an explosion within the large vessel. The ship sank in about twenty minutes off the coast of Ireland. The Germans attacked the boat because they thought the ship contained ammunition and other weapons for war, and they ended up being right. The U.S. was not happy, and even though Germany apologized, it was still a big factor for the U.S. to enter WWI.