Throughout its first century, military aviation helped advance the interests of the United States. From a curiosity, fragile and of uncertain value, the warplane has become a devastating weapon. Moreover, ballistic missiles and surveillance satellites have joined aircraft in this aerial array. In these volumes, we try to describe and analyze, in the context of national policy and international rivalries, the evolution of land-based air power since the United States Army in 1907 established an Aeronautical Division responsible to the Chief Signal Officer. This work, in addition to commemorating the Air Force's fiftieth anniversary, also commemorates almost one hundred years of progress in the design and use of aerial weaponry. By placing airmen and their machines in an appropriate context, it provides a clearer understanding of the central role of the Air Force in current American defense policy. Early in the conceptualization of this work, it was decided that a collaborative effort would make the best use of whatever special skills or knowledge each of contributor might possess. The history is divided into two volumes. Volume I, containing the first 12 chapters, begins with balloons and the earliest heavier-than-air machines. It carries the story through World War II to the establishment of the United States Air Force as a service separate from, but equal to, the Army and the Navy. Volume II picks up the narrative at the Korean War, takes it through the War in Southeast Asia, the Gulf War, to the drawdown following the end of the Cold War.