Since World War II erupted in Europe on 1 September 1939 after Nazi Germany invaded Poland, the United States had maintained its neutrality until the unannounced Japanese air attack on the American naval base at Pearl Harbor on 7 December 1941. In October 1940, China appealed to American president Franklin D. Roosevelt to allow the sale of military aircraft to China along with the recruitment of American pilots for the resistance war against the Japanese invasion. In December, Washington approved China's request to recruit American pilots who would resign from U.S. military services and volunteer to serve in the Chinese Air Force with significant monetary compensation. On 11 March 1941, the U.S. passed the Lend-Lease Act, which permitted the U.S. government to provide war equipment and material to Britain, France and other allied countries. On May 6, 1941, this policy was extended to China as well. With the full-scale war between the Soviets and Nazi Germany, all new fighter aircraft produced by the Soviets were now directed to the battlefronts against Nazi Germany. While the decision was made by the Americans to support Generalissimo Chiang Kai-shek in the War of Resistance against the Japanese with the Lend-Lease Act, much needed help also came by way of the American response to the Japanese invasion of French Indochina, which motivated the Americans to enact the U.S. scrap metal and oil embargo against Japan and the freezing of Japanese assets in summer of 1941.