What is a Division?

The Division: The Building Block of the US Army

The US Army is composed of various-sized units arranged in a hierarchical structure from the smallest to the largest in size and responsibility. A division is the smallest unit in the US Army capable of sustained, independent combat operations.

The Army division is structured to provide leadership, organization and logistics to smaller dependent combat and support units, such as brigades, regiments and battalions in descending order. Division headquarters carries out its missions by leading its subordinate units to defeat enemy forces, while supporting and managing those units to prepare them for future action.

The US Army has used temporary divisions since the Civil War. World War I made it clear that a more structured and permanent organization was needed. The US Army chose the division as the basic organization of the American Expeditionary Forces. In 1917, the first divisional unit created by the US Army for combat in Europe was the 1st Division.

Since 1917 the division has been the building block of the US Army. Over the years, it has changed in structure and has fluctuated between 10,000 and 28,000 soldiers. The division has survived over the years because of its success in adapting to changing circumstances, and by being the crucial organizational and command interface between smaller combat units and higher levels of command. The 1st Infantry Division has led the way in the success of the division as an essential unit of the US Army. Starting in 1939, the Army fielded types of divisions: infantry, armor, cavalry and airborne. The 1st Division—today’s 1st Infantry Division—is the Army’s first and oldest division, having been on continuous active duty since June 8, 1917.

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