This publication, Army Techniques Publication ATP 4-02.55 Army Health System Support Planning September 2015, replaces FM 8-55 and updates key planning topics while adopting current terminology and concepts as necessary. The AHS is a complex system of interrelated and interdependent systems which provides a continuum of medical treatment from point of injury or wounding through successive roles of medical care to definitive, rehabilitative, and convalescent care in the continental United States (CONUS), as required. Planning is an essential element which facilitates the successful accomplishment of the Army Medical Department (AMEDD) mission. The medical planner, by carefully applying AMEDD doctrine and principles, is able to provide the best possible AHS for all Army operations. The AHS provides support to forces deployed across the full range of military operations with its various operational arrangements. The AHS is a complex system of highly synchronized, interrelated and interdependent systems comprised of ten medical functions. It is a system of systems. The medical functions align with medical disciplines and specialty training with the capabilities required to provide state-of-the-art care to Soldiers regardless of where they are deployed or assigned. The functions include: medical mission command, medical treatment (area support), hospitalization, dental services, preventive medicine services, combat and operational stress control, veterinary services, medical evacuation, medical logistics, and medical laboratory. Army Techniques Publication 4-02.55 consists of four chapters and four appendixes as follows: Chapter 1 provides an overview of the characteristics of the AHS, its principles, functions, the role of medical care, and medical planning factors. It also discusses the fundamental aspects used by medical planners to determine the best possible AHS to support Army operations. Chapter 2 describes the ten medical functions and how they are aligned with specific medical disciplines of health service support (HSS) or force health protection (FHP) or sustainment medical tasks. It also provides the primary purposes of the functions to give the medical planner a planning reference point to work from. Chapter 3 provides guidance for some of the unique complexity inherent to AHS planning. It also provides a brief review of and references the Army planning process and how it applies to AHS planning. Chapter 4 discusses some of the many different and unique factors, terms, and computation the medical planner can use to develop the AHS estimate. Appendix A provides a detailed example of the AHS estimate with planning considerations. Appendix B provides an explanation of rate calculations and provides some of the more commonly used rate formulas. Appendix C provides an example and guidance on the preparation of an AHS appendix to an operation order (OPORD) or operation plan (OPLAN). Appendix D provides a methodology to manually calculate hospital bed requirements. It includes current and historical information to perform the calculations to assist in preparing the AHS estimate.