<P> The military effort was strongly supported by civilians on the home front, who provided the military personnel, the munitions, the money, and the morale to fight the war to victory . World War II cost the United States an estimated $341 billion in 1945 dollars--equivalent to 74% of America's GDP and expenditures during the war . In 2015 dollars, the war cost over $4.5 trillion . </P> <P> American public opinion was hostile to Hitler's Germany, but how much aid to give the Allies was controversial . Public opinion was even more hostile to Japan, and there was little opposition to increased support for China . By 1940 the U.S., while still neutral, was becoming the "Arsenal of Democracy" for the Allies, supplying money and war materials . The sudden defeat of France in spring 1940 caused the nation to begin to greatly grow its armed forces, including the first peacetime draft . After the German invasion of the Soviet Union in June 1941, America began sending Lend Lease aid to the Soviet Union as well as Britain and China . </P> <P> Prior to America's entry into World War II in December 1941, individual Americans volunteered to fight against the Axis powers in other nations' armed forces . Although under American law, it was illegal for United States citizens to join the armed forces of foreign nations and in doing so, they lost their citizenship, many American volunteers changed their nationality to Canadian . However Congress passed a blanket pardon in 1944 . American mercenary Colonel Charles Sweeny living in London began recruiting American citizens to fight as a US volunteer detachment in the French Air force, however France fell before this was implemented . During the Battle of Britain, 11 American pilots flew in the RAF, one of whom was killed, Charles Sweeney's nephew, also called Charles formed a Home Guard unit from American volunteers living in London . </P> <P> One notable example were the Eagle Squadrons, these were RAF Squadrons made up of American volunteers and British personnel . The first squadron was formed; No. 71 Squadron on 19 September 1940 by followed by No. 121 Squadron on 14 May 1941 and No. 133 Squadron on 1 August 1941 . 6,700 Americans applied to join but only 244 Americans got to serve with the three Eagle Squadrons, 16 Britons also served as squadron and flight commanders . The first Eagle Squadron became operational in February 1941 and the Squadrons scored their first kill in July 1941 . On 29 September 1942, the three squadrons were officially turned over by the RAF to the Eighth Air Force of the U.S. Army Air Forces and became the 4th Fighter Group, in their time with the RAF the squadrons claim to have shot, 731⁄2 German planes among them, 77 Americans and 5 Britons were killed . </P>

When did the united states get involved in world war ii