Military history of the United States during World War II
The military history of the United States during World War II covers the nation's role as one of the major Allies in their victory over the Axis powers. The United States is generally considered to have entered the conflict with the 7 December 1941 surprise attack on Pearl Harbor by Japan and exited it with the surrender of Japan on 2 September 1945. During the first two years of World War II, the U.S. maintained formal neutrality, which was officially announced in the Quarantine Speech delivered by President Franklin D. Roosevelt in 1937. While officially neutral, the U.S. supplied Britain, the Soviet Union, and China with war materiel through the Lend-Lease Act signed into law on 11 March 1941, and deployed the U.S. military to replace the British forces stationed in Iceland. Following the 4 September 1941 Greer incident involving a German submarine, Roosevelt publicly confirmed a "shoot on sight" order on 11 September, effectively declaring naval war on Germany and Italy in the Battle of the Atlantic. In the Pacific Theater, there was unofficial early US combat activity such as the Flying Tigers.
During the war, some 16,112,566 Americans served in the United States Armed Forces, with 407,316 killed and 671,278 wounded. According to the US Department of Defense, of the 407,316 dead, about 250,000 were killed in the European theater, the remaining 160,000 died in the Pacific War. There were also 130,201 American prisoners of war, of whom 116,129 returned home after the war. Key civilian advisors to President Roosevelt included Secretary of War Henry L. Stimson, who mobilized the nation's industries and induction centers to supply the U.S. Army, commanded by General George C. Marshall and the Army Air Forces under General Henry H. Arnold. The U.S. Navy, led by Secretary of the Navy Frank Knox and Admiral Ernest J. King, proved more autonomous. Overall priorities were set by Roosevelt and the Joint Chiefs of Staff, chaired by William D. Leahy. The defeat of the Nazis was the U.S.'s official highest priority per its agreement with Britain; however, in practice, the US devoted more resources to the Pacific than Europe and Africa until 1944.
Admiral King put Admiral Chester W. Nimitz, based in Hawaii, in charge of the Pacific War against Japan. The Imperial Japanese Navy had the advantage, taking the Philippines as well as British and Dutch possessions and threatening Australia. However, in June 1942, its main carriers were sunk during the Battle of Midway, and the Americans seized the initiative. The Pacific War became one of island hopping, so as to move air bases closer and closer to Japan. The Army, based in Australia under General Douglas MacArthur, steadily advanced across New Guinea to the Philippines, with plans to invade the Japanese home islands in late 1945. With its merchant fleet sunk by American submarines, Japan ran short of aviation gasoline and fuel oil, as the US Navy in June 1944 captured islands within bombing range of the Japanese home islands. Strategic bombing directed by General Curtis Lemay destroyed all the major Japanese cities, as the U.S. captured Okinawa after heavy losses in spring 1945. With the atomic bombings of Hiroshima and Nagasaki, the Soviet invasion of Manchuria, and the imminent invasion of the home islands, Japan surrendered.
The war in Europe involved aid to Britain, its allies, and the Soviet Union, with the US supplying munitions until it could ready an invasion force. U.S. forces were first tested to a limited degree in the Tunisian campaign and then employed more significantly with the British Forces in Italy in 1943–1945, where U.S. forces, representing about a third of the Allied forces deployed, bogged down after Italy surrendered and the Germans took over. Finally, the main invasion of France took place in June 1944, under General Dwight D. Eisenhower. Meanwhile, the U.S. Army Air Forces and the British Royal Air Force engaged in the area bombardment of German cities and systematically targeted German transportation links and synthetic oil plants, as it knocked out what was left of the Luftwaffe post Battle of Britain in 1945. Being invaded from all sides, it became clear that Germany would lose the war. Berlin fell to the Soviets in May 1945, and with Adolf Hitler dead from suicide, the Germans surrendered.
The American 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 $296 billion in 1945 dollars, and at their highest in 1945, military expenditures comprised 38% of the national GDP.
Origins
American public opinion was hostile to the Axis, but how much aid to give the Allies was controversial. The United States returned to its typical isolationist foreign policy after the First World War and President Woodrow Wilson's failure to have the Treaty of Versailles ratified. Although President Franklin D. Roosevelt personally favored a more assertive foreign policy, his administration remained committed to isolationism during the 1930s to ensure congressional support for the New Deal, and allowed Congress to pass the Neutrality Acts. As a result, the United States played no role in the Second Italo-Ethiopian War and the Spanish Civil War. After the German invasion of Poland and the beginning of the war in September 1939, Congress allowed foreign countries to purchase war materiel from the United States on a "cash-and-carry" basis, but assistance to the United Kingdom was still limited by British hard currency shortages and the Johnson Act, and President Roosevelt's military advisers believed that the Axis Powers would be defeated and that US military assets should be focused on defending the Western Hemisphere.By 1940, the US, while still neutral, was becoming the "Arsenal of Democracy" for the Allies, supplying money and war materials. Prime Minister Winston Churchill and President Roosevelt agreed to exchange 50 US destroyers for 99-year-leases to British military bases in Newfoundland and the Caribbean. The sudden defeat of France in spring 1940 caused the nation to begin to expand its armed forces, including the first peacetime draft. In preparation for expected German aggression against the Soviet Union, negotiations for better diplomatic relations began between Undersecretary of State Sumner Welles and Soviet Ambassador to the United States Konstantin Umansky. 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. Although President Franklin D. Roosevelt's advisers warned that the Soviet Union would collapse from the Nazi advance within weeks, he barred Congress from blocking aid to the Soviet Union on the advice of Harry Hopkins. In August 1941, President Roosevelt and Prime Minister Churchill met aboard the USS Augusta at Naval Station Argentia in Placentia Bay, Newfoundland, and produced the Atlantic Charter outlining mutual aims for a postwar liberalized international system.
Public opinion was even more hostile to Japan, and there was little opposition to increased support for China. After the 1931 Japanese invasion of Manchuria, the United States articulated the Stimson Doctrine, named for Secretary of State Henry L. Stimson, stating that no territory conquered by military force would be recognized. The United States also withdrew from the Washington Naval Treaty limiting naval tonnage in response to Japan's violations of the Nine-Power Treaty and the Kellogg–Briand Pact. Public opposition to Japanese expansionism in Asia had mounted during the Second Sino-Japanese War when the Imperial Japanese Army Air Service attacked and sank the US Yangtze Patrol gunboat in the Yangtze River while the ship was evacuating civilians from the Nanjing Massacre. Although the US government accepted Japanese official apologies and indemnities for the incident, it resulted in increasing trade restrictions against Japan and corresponding increases of US credit and aid to China. After the United States abrogated the 1911 Treaty of Commerce and Navigation with Japan, Japan ratified the Tripartite Pact and embarked on an invasion of French Indochina. The United States responded by placing a complete embargo on Japan through the Export Control Act of 1940, freezing Japanese bank accounts, halting negotiations with Japanese diplomats, and supplying China through the Burma Road.
American volunteers
Before America entered 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 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 Royal Air Force. Charles Sweeney's nephew, also named Charles, formed a Home Guard unit from American volunteers living in London.One notable example was the Eagle Squadrons, which were RAF squadrons made up of American volunteers and British personnel. The first to be formed was No. 71 Squadron on 19 September 1940, 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 got to serve with the three Eagle squadrons; 16 Britons also served as squadron and flight commanders. The first 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 US Army Air Forces and became the 4th Fighter Group. In their time with the RAF the squadrons claim to have shot 73½ German planes; 77 Americans and 5 Britons were killed.
Another notable example was the Flying Tigers, created by Claire L. Chennault, a retired US Army Air Corps officer working in the Republic of China since August 1937, first as military aviation advisor to Generalissimo Chiang Kai-shek in the early months of the Sino-Japanese War. Officially known as the 1st American Volunteer Group but nicknamed the "Flying Tigers", this was a group of American pilots already serving in the US Armed forces and recruited under presidential authority. As a unit they served in the Chinese Air Force against the Japanese. The group comprised three fighter squadrons of around 30 aircraft each. The AVG's first combat mission was on 20 December 1941, twelve days after the Pearl Harbor attack. On 4 July 1942 the AVG was disbanded, and was replaced by the 23rd Fighter Group of the United States Army Air Forces, which was later absorbed into the US Fourteenth Air Force. During their time in the Chinese Air Force, they succeeded in destroying 296 enemy aircraft, while losing only 14 pilots in combat.