NOTICE! TRAVELLERS intending to embark on the Atlantic voyage are reminded that a state of war exists between Germany and her allies and Great Britain and her allies; that the zone of war includes the waters adjacent to the British Isles; that, in accordance with formal notice given by the Imperial German Government, vessels flying the flag of Great Britain, or any of her allies, are liable to destruction in those waters and that travellers sailing in the war zone on the ships of Great Britain or her allies do so at their own risk.
–IMPERIAL GERMAN EMBASSY,
Washington, DC, April 22, 1915

What is the greatest risk Germany took by establishing this policy?

wasting its energy chasing down passenger ships
harming innocent people and making new enemies
angering the British by denying them war supplies
failing to prevent delivery of supplies by other routes