The German leaders decided to use submarines. These submarines were named U-boats, from the German word Unterseeboot (meaning underwater boat). The U-boats attacked passenger ships such as RMS Lusitania carrying civilians to the United Kingdom. They did not follow the laws of war, because the British would be able to easily destroy them if they did. America was selling weapons to Germany's enemies but not to Germany, thus not being neutral ("neutral" means to not take a side during a conflict). Many American and British noncombatants were killed by the submarines.