 Soon after World War I erupted in Europe, it became evident that the airplane was forcing a permanent change in warfare. By the time America entered the war on April 6, 1917, the airplane was well established as a military weapon. But the United States had only a small number of pilots and very few training planes. There were no bombers, fighters, or other combat-type airplanes. American air power ranked 14th in the world. Secretary of War Baker urged the nation to back the build-up of a vast air fleet. Congress rushed through a bill appropriating $640 million for the build-up of American airstream, and President Wilson signed it on July 24, 1917. A large-scale production of airplanes was initiated. Among them was the courthouse JN-4 called the Jenny. This two-seater was selected as the standard pilot training plane. The British-designed de Havilland-4 was adopted as the standard front-line bomber plane for combat. The famous American Liberty Engine was developed to power the DH-4, and it became one of America's greatest contributions to aviation during that era. 543 of the American-built DH-4 saw combat before war then, serving a dual role as observation plane and bomber. Not only were airplanes needed in large quantities, but men had to be trained to fly and maintain them. The Air War in Europe stirred America's young men. There was no shortage of volunteers. In the year following the declaration of war, over 38,000 of America's youth had volunteered for flying training with the Army. Training them was a mammoth undertaking. Successful applicants were sent first to ground school for an intensive eight-week course. Then they began flight training. This was divided into three phases. Dual instruction, solo practice, and cross-country training. Successful completion of these phases earned the flyer his commission and the right to wear the wings of a military aviator. When state-side training was completed, the new pilots were sent overseas, where they were taught to fly combat planes. Although the first American flying unit didn't arrive in Europe until September 1917, some Americans had already flown combat with the British and French beginning in 1915. Many of them flew with the famous Lafayette Eskidrill. After the United States entered the war, many of these pilots transferred to the air service. The nucleus of the 103rd Aero Squadron was made up of former members of the Lafayette Eskidrill. The 103rd was the first American squadron to see action as a unit. The 94th Pursuit Squadron became the first American-trained flying unit to see combat. The 94th was the famous Hat and the Ring Squadron, later commanded by Captain Eddie Rickenbacker, who became America's top ace in World War I with 26 victories. More American squadrons joined those already committed to battle. As the intensity of the war increased, so did the involvement of the American air services. As an example, American pilots flew over 3,300 sorties during a 5-day period in September of 1918. Great battles raged, both in the air and on the ground. The Germans attempted to smash the Allies before the influence of American forces could swing the tide of the war. It took large concentrations of air power to counter the German efforts. The Allies planned an all-out effort to wipe out the large German salient at San Miguel. The battle plan included the first independent attack by the American Army, and it called for a large air offensive. Colonel Billy Mitchell was to command the largest aggregation of air forces ever committed, up to that time, to a single operation during the war. Flying both American-built DH-4s as well as French and English-built planes, the Americans and French enjoyed numerical superiority for the first time. On the opening day of the battle, Mitchell committed 1,500 planes. He proved his theories on the effectiveness of concentrated air power, as his aircraft entered combat on the third day of the battle. Bombing and strafing helped to demoralize German ground troops, and was a major factor in forcing the Germans out of the San Miguel sails. Mitchell's aerial tactics were repeated during the Musard Dawn offensive in late September, accomplishing the greatest single aerial triumph of the war. The Allied Air Armada fought off waves of Germany's best planes and pilots. The already weakened Germany was unable to launch a planned counter-offensive. The defeat of Germany loomed closer. By the end of the war, November 11th, 1918, 71 Americans qualified as aces, each credited with shooting down or sharing the destruction of five or more German planes. Their total score was 450 planes and 50 balloons. A few of the never-to-be-forgotten American aces were Lieutenant Frank Luke, Major Raoul Lufverry, and the ace of aces, Captain Eddie Rickenbacker. Six months before the war ended, an event took place in the States, which influenced the evolution of American air power. On May 15th, Army fliers inaugurated America's first airmail service. In the years following, airmail pilots established routes and a system of airways that are still being utilized. Many ex-military fliers wanted to stay in aviation, but there were very few jobs for civilian pilots. Some bought surplus Army planes and flew them anywhere they could make a dollar, carnivals, county fairs, exhibitions. These barnstormers often made money by taking passengers for their first plane ride. Some earned a living by stunt flying, a very dangerous business which left crowds fell down. Many of these barnstormers invested in bigger planes and helped develop intercity taxi service, the stepping stones to today's commercial airlines. During the 20s, fliers accepted many challenges. They strived to fly higher, faster, and farther. Builders began to develop better planes, engines, and navigation equipment. Record flights came rapidly. One was the cross-country non-stop flight from New York to California. After two unsuccessful attempts, Army lieutenants McCready and Kelly took off from Long Island in May 1923. Just under 27 hours later, they landed in California, the first fliers to complete a non-stop coast-to-coast flight. One year after the record-breaking cross-country flight, four specially built Douglas World cruisers took off from a lake near Seattle on the first leg of an historic flight around the world. 175 days later, two of the original four Air Service planes returned to Seattle to successfully complete the 26,000-mile journey. By the time the name of the Air Services was changed to the Air Corps in the mid-20s, Army fliers had set numerous records and continued to work for technological advancement. Cold weather testing improved the ability of men and planes to operate in sub-zero temperatures. New speed records were set in 1925 when lieutenants Side Betis and Jimmy Doolittle won the Pulitzer and Schneider Cup races respectively within a two-week span. One month after Lindbergh's historic flight in May 1927, another flying achievement was accomplished by two Air Corps pilots, lieutenants L.J. Madeleine and A.F. Heggenberger. Taking off from California, they flew a Fokker Trimotor monoplane named the Bird of Paradise, non-stop to Hawaii in 25 hours and 50 minutes. With their destination a mere dot in the Pacific Ocean, their flight demanded exceptional navigation, superb flying skills, and real courage. In 1929, Air Corps fliers established an unofficial world flight endurance record in another Trimotor Fokker named the Question Mark. Using a mid-air refueling technique developed in 1923, aerial fuel transfers were successfully accomplished 43 times, nine of which were performed at night. The Question Mark, commanded by Major Carl Spotz and including Captain Ira C. Eaker and Lieutenant Elwood R. Casada among its crew, stayed aloft for almost 151 hours, landing only after one engine began to give them trouble. The decade of the 20s is often referred to as the Billy Mitchell era. Following World War I, General Mitchell was the chief proponent of air power, and he strongly voiced the opinion that America must maintain strong air defenses. Mitchell believed that bombers would spell the end of sea power. He asked for the opportunity to prove the effectiveness of air power over naval forces. The combined war and Navy departments granted his wish and gave him the chance to prove his theories. On two separate occasions, U.S. airplanes carried out attacks on warships that were going to be scuttled or scrapped, including the powerful German battleship Ostfriesland. Mitchell's bombers sank some of the supposedly unsinkables, including the U.S. battleships Alabama, New Jersey, and the Virginia. Many years were to pass before the significance of these bombing tests was fully recognized, as witnessed the destruction of American ships of the Pacific Fleet at Pearl Harbor. The decade of the 20s spawned many pioneers in aviation. Some of the names high on the list of non-military aviators were Amelia Earhart, Wiley Post, and the Lone Eagle Charles A. Lindberg. Considering the distinctive progress in aviation in the 20s, it seems justifiable that many historians turned this period a golden age of aviation.