Members of the combat service support branches, like their comrades in the other branches, prepare plans, estimates, and orders participate in the development of doctrine and materiel and conduct training in their respective specialties. Its forces provide immediate support as organic elements of the forward combat units (battalions, brigades, divisions, and corps), as well as administrative and technical services in rear areas and at the highest national level. At the tactical level of war, it includes but is not limited to that support rendered by service troops in ensuring the operational and tactical aspects of supply, maintenance, transportation, health services, and other services required by aviation and ground combat troops to permit those units to accomplish their missions in combat.” Thus, combat service support incorporates those functions necessary to man, arm, feed, fuel, maintain, and move the fighting forces and their equipment in the field. According to the official armed forces definition, combat service support covers “the essential logistic functions, activities, and tasks necessary to sustain all elements of operating forces in an area of operations. Finally, the combat service support branches include the Adjutant General's Corps, the Chaplain's Corps, the Finance Corps, the Judge Advocate General's Corps, the Military Police Corps, the Ordnance Corps, the Quartermaster Corps, the Transportation Corps, and the six branches of the Army Medical Service. In many respects, the Signal Corps and the Chemical Corps also perform both functions.

Army Corps of Engineers is considered both a combat arm and a combat support branch in that engineers perform direct combat missions as well as support functions. The combat support branches include the Corps of Engineers, the Military Intelligence Corps, the Chemical Corps, and the Signal Corps. The combat arms (branches) are Infantry, Armor, Artillery, Air Defense Artillery, Aviation, and Special Forces. The basic and special branches of the army are aligned with the three functional categories. Rather, officers and enlisted personnel are detailed to the General Staff Corps or Inspector General's Corps for limited periods and then return to their basic branch. The General Staff Corps and the Inspector General's Corps are not in fact separate branches at all, even though they have distinctive insignia. One additional special branch, Civil Affairs, is found only in the reserve components. Technical services include the Corps of Engineers, Army Medical Service, and the Chemical, Ordnance, Quartermaster, Signal, and Transportation Corps. The Adjutant General's, Chaplain's, Finance, Judge Advocate General's, and Military Police Corps are considered administrative services. The special branches include the Chaplain's and Judge Advocate General's Corps and the six branches of the Army Medical Service (the Medical, Dental, Veterinary, Army Nurse, Army Medical Service, and Medical Specialist Corps). The basic branches are: Armor, Artillery, Air Defense Artillery, Aviation, Infantry, Military Intelligence, and Special Forces the Corps of Engineers and the Adjutant General's, Chemical, Finance, Military Police, Ordnance, Quartermaster, Signal, and Transportation Corps. With the exception of general officers, every officer, soldier, and unit of the army is assigned to one of the army's twenty‐five basic and special branches. This division of forces into three functional groups applies specifically to the army, but navy, Marine Corps, and air force units and personnel fall into the same general categories. Combat service support forces provide administrative and technical (logistical) services to ensure that the combat and combat support forces are adequately manned, armed, fed, fueled, maintained, and moved as required. Combat support forces provide direct support of the forces on the battlefield by providing intelligence, communications, engineering, and chemical warfare services of immediate impact on the course of the battle. Combat forces engage in direct confrontation with enemy forces to kill or capture them, to break their will to continue the fight, and to seize and hold terrain or to deny it to the enemy. Army, and army forces are divided into three categories according to their function on the battlefield: combat, combat support, and combat service support.

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