From breaking wild horses in Colorado to fighting the Red Baron's squadrons in the skies over France, here in his own words is the true story of a forgotten American hero: the cowboy who became our first ace and the first pilot to fly the American colors over enemy lines.     Growing up on a ranch in Sterling, Colorado, Frederick Libby mastered the cowboy arts of roping, punching cattle, and taming horses. As a young man he exercised his skills in the mountains and on the ranges of Arizona and New Mexico as well as the Colorado prairie. When World War I broke out, he found himself in Calgary, Alberta, and joined the Canadian army. In France, he transferred to the Royal Flying Corps as an "observer," the gunner in a two-person biplane. Libby shot down an enemy plane on his first day in battle over the Somme, which was also the first day he flew in a plane or fired a machine gun. He went on to become a pilot. He fought against the legendary German aces Oswald Boelcke and Manfred von Richthofen, and became the first American to down five enemy planes. He won the Military Cross for conspicuous gallantry in action.   Libby's memoir of his cowboy days in the last years of the Old West evokes a real-life Cormac McCarthy novel. His description of World War I combines a rattling good account of the air war over France with captivating and sometimes poignant depictions of wartime London, the sorrow for friends lost in combat, and the courage and camaraderie of the Royal Flying Corps. Told in charming, straightforward vernacular, Horses Don't Fly is an unforgettable piece of Americana.