In summer 1941 the British appealed to Americans to conserve food to provide more to go to Britons fighting in the Second World War. The Office of Price Administration warned Americans of potential gasoline, steel, aluminum and electricity shortages. It believed that with factories converting to military production and consuming many critical supplies, rationing would become necessary if the country entered the war. It established a rationing system after the attack on Pearl Harbor. In June 1942 the Combined Food Board was set up to coordinate the worldwide supply of food to the Allies, with special attention to flows from the U.S. and Canada to Britain.