The year 1917 was dominated by the Russian Revolution and America entering the war. On 3 February, America cut diplomatic ties with Germany following the announcement on 31 January that Germany would begin unrestricted submarine warfare. All III U-boats were ordered to sink any vessel at will. The hope was a Britain would be starved into submission. America declared war on 6 April and US destroyers joined the fight against the U-boats while US battleships joined the Grand Fleet at Scapa Flow. Losses the submarines were now so great that Britain was in danger of running out of food and the convoy system was brougth into force.