Evolution of US Army Divisional Structures
Prior to World War I, the regiment was the Army's largest fixed administrative and tactical command. During World War I, regiments combined into brigades to form infantry divisions. Each division had two infantry brigades; each brigade had two regiments. Field artillery and service units supported each brigade.
World War II divisions were infantry, armored, cavalry, airborne, and motorized. Brigade headquarters were eliminated to streamline the divisions. This meant the division commander directly commanded three regiments, supported by engineer and service units and four field artillery battalions. Regiments were still responsible for their own administration and logistics.
Combat commands replaced regiments in some armored divisions. Each combat command had attached tank and armored infantry battalions. Combat commands were tactical operations control headquarters. The logistics and administrative operations extended from division level directly to the battalions. Battalions cross-attached companies to form task forces. Cavalry provided reconnaissance and security and was grouped as the situation demanded. Armored field artillery battalions and engineer companies normally supported the combat commands.
In the late 1950s, the Army reorganized each infantry division into a "pentomic division" with five battle groups in preparation for tactical nuclear war in Europe. These groups were, in effect, large battalions. Each battle group had five rifle companies, a combat support company, and appropriate field artillery and service support. The battle groups were self-sustaining, could be employed singly or in combinations, and remained largely unchanged during the 1950s.
The pentomic division structure was abandoned in the early 1960s when the Army adopted for all divisions the combat command organization of the armored division. Combat commands were renamed brigades. Each division had three brigade headquarters into which various numbers of battalions could be grouped. All divisions were similarly organized. Some were heavy (armored or mechanized) and some were light (infantry and airborne), depending on the mission and types of battalions assigned.
In the mid-1960s, the Army added the air assault division. Principal differences between divisions were in the types of battalions assigned and the composition of the division base. Divisions also differed in how they entered into combat. The war in Vietnam was fought primarily with airmobile and infantry divisions.
During the 1980s, the Army fielded a motorized division and several light infantry divisions. The motorized division could rapidly deploy to a contingency area, establish or expand a lodgment, and defeat enemy forces ranging from light infantry to tank and motorized forces. Light divisions provided versatility and strategic flexibility through their capability for rapid deployment.
The early 1990s brought significant changes to the world and the Army. The motorized division was deleted from the force structure. The dissolution of the Soviet Union and the apparent end of the Cold War presented threats that were more ambiguous and regionally focused. The US Army's current warfighting doctrine reflects the nature of modern warfare. It is inherently joint doctrine, recognizing the teamwork required of all the services.
US Army divisions conduct Army operations both in war and other than war arenas. All divisions are generally organized with a similar basic design. This design comprises a division headquarters and headquarters company (HHC), three ground maneuver brigades, an aviation brigade, a division artillery, a support command, a cavalry squadron, an air defense artillery battalion, an engineer battalion or brigade, a signal battalion, a military intelligence battalion, a military police company and, in most cases, a chemical company.