noun
battalion; large force
Refers to a large military unit, typically a battalion or a sizable force. Can also be used figuratively for a large group of people working together.
敵の大部隊が国境に集結している。
A large enemy force is massing at the border.
彼は大部隊を率いて前線に向かった。
He led a battalion to the front line.
大隊 is the standard military term for 'battalion', whereas 大部隊 is a broader term for any large force, not necessarily a formal battalion.
Compound of 大 (large) and 部隊 (unit, force).