The United States In the War
Japan's carrier-plane attack on Pearl Harbor, Hawaii, December 7, 1941, brought the United States into the war. War was formally declared by Congress on the following day, and declarations of war between the United States and Germany and Italy were exchanged on December 11.Declaration of war. Franklin Delano Roosevelt signing the declaration of war against Japan.
Because of peacetime conscription, the United States had a million trained men under arms when the warbegan. Eventually an army of 11,260,000 was raised, including 90 divisions of ground forces and 2,340,000 men in the Air Forces. The Navy raised 4,183,000 men, the Marines 669,000.
A naval expansion program had been adopted in July, 1940, and construction of new ships was pushed vigorously. By 1945 the U.S. Navy had become the largest naval force ever afloat, with 10,562 ships, including 1,258 warships.
While the United States had built many planes for the Allies, the Army Air Corps was still weak in 1941. In 1945 it had 69,000 planes. During the war the United States devoted virtually all of its material resources to the war effort. When the war began, however, the United States was ill equipped.