On the morning of May 1, 1915, a warning appeared in U.S. newspapers. Germany published a notice to Americans not to travel on British ships -- Germany and England were at war, and British ships were targets. That was the morning the Lusitania set sail, and her passengers probably never saw the notice.
The British passenger ship Lusitania was heading from New York to Liverpool, loaded with civilian passengers. Six days into her voyage, a German submarine spotted her and fired a torpedo without warning. The torpedo struck the ship and caused a second explosion onboard. Britain claimed the second explosion resulted from coal dust; Germany claimed it was gunpowder. The ship sank in 20 minutes off the southern coast of Ireland, killing approximately 1,200 people and igniting a controversy that could have changed the course of history.
Britain claimed the Lusitania was a civilian ship with no military ties. Germany claimed the Lusitania was in fact carrying munitions for the Allies. When the ship sank with more than 100 Americans onboard, the U.S. population called for military action against Germany. U.S. President Wilson resisted the cries for war, and instead insisted on reparations from Germany. Although Germany maintained that there were munitions on the ship, she eventually took responsibility for the misdeed. This helped to delay U.S. involvement in World War I. Later, WWI recruitment posters would read "Remember the Lusitania."
Years after the incident, British documents revealed that the ship was in fact carrying munitions for the Allies. The Lusitania was transporting 4.2 million rounds of Remington .303 rifle cartridges, 1,250 cases of shrapnel shells and 18 cases of fuses. And according to the Discovery Channel, at the outbreak of the war in 1914 the Lusitania had been fitted with a broadside for potential use by the Royal Navy.