1921 to 1933 the Division was structured around the horse riding concept in defined Regiments.
1933 to 1943 the Division was structured around the Triangle mechanized and motorized concept.
1943 to 1949 the Division was changed to the square concept as mainly a Infantry Division for fighting in the jungles of the Pacific.
1949 to 1957 The Division was changed to the Triangular Division. The 5th, 7th and 8th Cavalry Regiments were retained and the 12th Cavalry Regiment was deactivated. This was for Korean War and duty on the Korean DMZ.
1957 to 1964 The Division was changed to the Pentomic structure into Battle Groups
1965 to 1971 The Division became Air Mobile structure as they deployed to Vietnam.
1971 to 1975 The Division was configured into the TRICAP (Triple Capability) Division was organized with Armored, Infantry and Air Cavalry Brigades.
1975 to 2001 The division was converted to an Armored Division.
2001 to 2005 The Division had initiated a series of unit change overs of the division organization and equipment replacements to support and field the FORCE XXI integrated combat system capabilities.
2005 to 2013 The division Division was reorganized and transitioned to a (Modular) Modified Table of Organization and Equipment (MTOE) Unit of Action.
2013 to 2016 The Division implementing ARFORGEN, a transformational force generation model. This returned the Division Artillery, The 4th BCT was inactivated, The Sustainment Brigade was renamed and added, All STBs within the Division were inactivated.
2016 to present The Army announced a pilot program, 'associated units', in which a National Guard or Reserve unit would now train with a specific active Army formation. These units would wear the patch of the specific Army division before their deployment to a theater.
