Echelons I and II are provided by the operating forces as part of their table of organization and manning documents. Echelons III and IV are provided from service component resources in support of casualties generated by combat. Evacuation to Echelons I, II, and III is the responsibility of the component commander. Evacuation from Echelon III to Echelon IV is the responsibility of the unified command. Patients are evacuated to the echelon that will provide the level of care required to expedite their return to duty.
Tactical evacuation is a responsibility of the theater commander.
Requirements for mobility of medical personnel and facilities. Capabilities, equipment, and supplies of HSS personnel. The workload at each echelon of care, relative to its treatment capacity. Casualties are evacuated through the HSS system until they reach a facility capable of beginning decisive intervention, with sufficient time to perform necessary procedures and the bed capacity to retain the patient. This MTF or echelon of care is defined as the site of principal treatment.