From the early days of hot air ballooning to supersonic aircraft, High Frontier chronicles the history of flight in Pennsylvania. Early experimentation with lighter-than-air craft in the nineteenth century was followed by significant advances in aerodynamics, the advent of the airplane, and its gradual acceptance by the public. The state had its own contingent of inventors and aviators, who flew and crashed their homemade machines in countless exhibitions. After World War I commercial flights took wing, including government airmail delivery, and expanded airports, federal and state regulation of aeronautics laid the groundwork for the growth of the industry.