From the Preface: The following pages provide a narrative analysis of the U.S. Army's development of armored organizations and their related doctrine, materiel, and training activities in the period 1917-1945. This period marked the emergence of clear principles of armored warfare that became the underpinning of the Armor Branch, influencing armored developments long after World War II ended. A unique style of mounted maneuver combat emerged that reflected a mix of tradition an innovation. In the process, American military culture changed, particularly through the adoption of combined-arms principles. Conversely, political actions, budgetary considerations, and senior leadership decisions also shaped the course of armor development. The emergence of an American armored force involved more than simply tank development. It included the creation of an armored division structure steeped in combined-arms principles, organizational flexibility, and revolutionary command and control processes. Parallel developments included the establishment of specialized units to provide antitank, reconnaissance, and infantry support capabilities. Several Army branches played a role in determining the precise path of armored development, and one of them-the Cavalry-became a casualty as a result.