- The Sussex Pledge was a commitment by the German Empire, given to the United States in May 1916, that it would not sink merchant ships without warning or without saving the lives of non-combatants.
- The pledge was made in response to the sinking of the British passenger ship RMS Sussex by a German U-boat, which had left the liner's passengers and crew stranded in lifeboats for hours before being rescued.
- The sinking of the Sussex caused outrage in the United States which came close to entering the First World War on the side of the Allied powers.
- Although Germany apologized for the Sussex incident and promised to change its U-boat tactics, it quickly became apparent that the German military could not or would not adhere to the pledge.
- In February 1917, Germany resumed unrestricted submarine warfare, sinking merchant ships without warning and killing thousands of civilians.
- This action by Germany was one of the main reasons that the United States declared war on Germany on April 6, 1917.