A British ship carrying hundreds of American passengers and weapons that was torpedoed by a German U-Boat. This helped America enter the war as the population began to view Germany as an enemy.
Lusitania is a ship that was sunk in World War One by one German U-boat. It was an English ship manufactured by the Cunard line and is considered by many as a major reason the USA entered WW1. It was a passenger vessel and therefore should not have been a military target, although it is suspected that it was used my England to illegally smuggle explosives into the country from America. This is based on reports of two huge explosives that caused the ships sinking. One from the torpedo from the U-boat and one from the explosives in the hold blowing up as a result of the U-boats attack. This theory of arms smuggling has never been fully proven though the English or Irish Navy were responsible for depth charging the remains of the wreck in the 1950's - as underwater recovery and diving technology improved meaning further exploration of the disaster would be possible. This is seen by many as an attempt to cover up evidence. Thousands of people died the night the ship sank many of them Americans and that is one of the reasons the US went to war in Europe.
On further review the Lusitania was carrying war weapons to Great Britain.