Worried that the Soviets would not be able to hold out, the United States and Great Britain promised aid to Joseph Stalin. On July 12, Great Britain and the Soviet Union had pledged mutual assistance against the Nazis and agreed that neither would pursue peace with Germany without the other's consent. Although British prime minister Winston Churchill despised Communism, he also valued anyone who fought against the Nazis. Just before the Germans had attacked the Soviet Union, Churchill had remarked that if Hitler invaded hell, he would consider a favorable reference to the Devil.
Also in July, U.S. president Franklin D. Roosevelt sent his aide Harry Hopkins to meet with Stalin in Moscow to determine Soviet supply needs and judge their willingness to fight. Hopkins' report on Soviet grit and determination helped Roosevelt convince Congress to include the USSR in the Lend-Lease program.
American supply ships soon joined with British and other Allied vessels sailing across the Atlantic to the Soviet Union in some of the most dangerous naval voyages of the war. Although the British and other nations also aided the Soviets, the American Lend-Lease program provided the vast majority of materiel help.