This thesis addresses the evolution of integrated close air support CAS from its birth to the present. By comparing three air arms development of CAS, it provides a historical bedrock for the controversies and discord that surround debate regarding the tactic. Viewing CASs air-ground synergy is a key design of the thesis, as many in the past have viewed it from only one side of the argument. The introduction defines and considers both the air and ground elements as essential to integrated CAS. Chapters One through Three outline the detailed histories of the tactics development by three air arms. Based on in-depth research, the conclusion emerges that the German Luftwaffe, the US Marine Corps, and the US Army Air Forces all conceived of the tactic concurrently, but evolved it through different priorities, pressures, and personalities.Historical chronology serves as a primary scaffold for the thesis, while the leadership of men in three separate air arms provides a secondary construct. Wolfram von Richthofen, Keith McCutcheon, and Elwood Pete Quesada were military leaders and innovators from different backgrounds. Their commonalities included dedicated, forceful leadership, tactical and operational prowess, and a focus on air-ground synergy. The thesis continues with the first year of US involvement in the Korean Conflict as a cautionary tale for integrated CAS. Many of the insights from late stage World War II CAS had to be relearned by the USAF during the Korean CAS Controversy. The thesis concludes with a review and then supposition based upon the glide-path established by nearly 100 years of CAS. The thesis ends with integrated CASs effects on the enemies of 3rd Battalion 1st Marines during the Second Battle of Fallujah. This section views the art and science of CAS in modern high intensity urban combat.