Great Britain declared the North Sea a war zone in the Winter. No protest was made by the United States or any neutral. Great Britain held up all neutral ships carrying non-contraband goods, detaining them, buying or confiscating their cargoes.
Great Britain constantly changed the contraband lists, so no foodstuffs of any kind have actually reached Germany since the war began. International law says foodstuffs destined for the civil population must pass. It does not recognize any right to starve out a whole people.
As a consequence, and in retaliation, Germany declared the waters around England a war zone, and started a submarine warfare. It became known in February that British ships were flying the American flag as a protection.
Great Britain replied by officially declaring its purpose to starve 120,000,000 Germans and Austrians. The United States very thoughtfully tried to mediate, proposing that foodstuffs should be passed and submarine warfare be stopped.
Germany agreed; England turned the proposal down. Then, in order to protect American passengers, they were warned by public advertisement of the danger of sailing under the flag of a belligerent.
Vessels carrying contraband of war are liable to destruction unless they can be taken to a port of the country that captures them. The right of search need not be exercised if it is certain such ships carry contraband.
Oil is contraband, like war ammunition and all metals. The master of the Gulflight (an American oil tank steamer sunk recently) swore before customs officials to his cargo of oil for France.
The master of the Lusitania similarly swore to his manifest of cargo of metals and ammunition. Both the Gulflight and the Lusitania carried contraband when attacked, it is obvious.
The Lusitania's manifest showed she carried for Liverpool 260,000 pounds of brass; 60,000 pounds of copper; 189 cases of military goods; 1,271 cases of ammunition, and for London, 4,200 cases of cartridges.
Vessels of that kind can be seized and be destroyed under The Hague rules without any respect to a war zone. The Lusitania was a British auxiliary cruiser, a man-of-war. On the same day she sailed the Cameronia, another Cunarder, was commandeered in New York Harbor for military service.