United States Air Force (USAF), one of the major components of the United States armed forces, with primary responsibility for air warfare, air defence, and the development of military space research. The Air Force also coordinates air services with the other military branches.The Union Balloon Corps and the balloon Intrepid Union Army Balloon Corps ground crew filled the balloon Intrepid at Fair Oaks, Virginia, in May 1862, during the American Civil War.U.S. military activities in the air began with the use of balloons by the army for reconnaissance during the American Civil War and the Spanish-American War. The Aeronautical Division of the Signal Corps of the U.S. Army was created on Aug. 1, 1907. Congress passed the first appropriations for aeronautics in 1911 and on July 18, 1914, created the Aviation Section of the Signal Corps. (For the development of naval aviation, see The United States Navy.)The first use of military aircraft, in an action against Pancho Villa in Mexico in 1916, was a failure. The next year the United States entered World War I with one ill-equipped air unit, the 1st Aero Squadron. The Appropriations Act of July 24, 1917, provided increased funds, and an executive order of May 20, 1918, removed aviation from the Signal Corps by establishing the U.S. Army Air Service. By the war’s end, the Air Service had attained a strength of 195,000 officers and men and had organized 45 squadrons with a complement of 740 planes. Until the later stages of the war, U.S. squadrons in France were equipped mainly with British and French planes.