The German submarine attacked on merchant ships off the south coast of Ireland and this action prompted the British Admiralty to warn the Lusitania ship to avoid the area or take simple evasive action such as zigzagging to confuse U-boat submarine plotting the vessel's course.The captain of Lusitania ignored these recommendations and the ship was hit by an exploding torpedo.
The justification given by Germany was that by stating correctly that Lusitania was an enemy ship and that it was carrying munitions.