The American Civil War introduced the operational level of war and with its introduction came one of the greatest challenges ever confronted by military commanders--operational command and control. In that regard, the objective of this monograph is to determine by what means high level Civil War commanders, here defined as army or army group equivalent, dealt with that challenge. First, the characteristics of the war that led to its being considered the first conflict to experience "operations" is described. Second, the command structure and general staff organization of late Civil War Union field armies is addressed. A description of the different means of exercising command and control over those armies form the main body of this study and includes the roles played by staffs, aerial telegraphy and electro-magnetic telegraphic systems. Finally, an example of the ways in which the various command and control means were used is offered through an analysis of the planning and early execution of the Union Army's 1864 spring offensive--Grant's final campaign.