The Lusitania is struck by a torpedo

The Lusitania sailed from New York Harbor to Liverpool in the UK in the Spring of 1915. She was sunk by a German hunter submarine the U-10. The furor over the sinking of a civilian passenger liner helped drive America into joining the Allies during WWI.

Though there were two large explosions, we now know that the U-10 only fired one torpedo. The second and fatal explosion was most likely cause by munitions that the ship was secretly carrying to the allies.