army corps
A military unit larger than a division, typically consisting of two or more divisions. Used in historical and modern military contexts.
The army corps was deployed to the front line.
The government organized a new army corps.
The general led the army corps to the front line.
The enemy's army corps is advancing toward the border.
師団 refers to a division, a smaller military unit than 兵団 (a corps made up of multiple divisions), so the two are easily confused in scale.
Compound of 兵 (hei, 'soldier') and 団 (dan, 'group, corps'). The term is a modern military coinage, likely from the Meiji period when Western military structures were adopted.