The 1BCT, which consists of about 3,500 people, was placed on lockdown for a few hours on Wednesday while military police searched for the ammunition.
So far, it has not been found.
The ammo is typically stored in an above-ground depot, and in a secure area. Specially-trained handlers are responsible for its safekeeping.
Officials say any time ammunition goes missing, there is concern, and they are taking this incident seriously.
But, they add, there is no reason at this point to believe the ammo was taken intentionally.
The ammunition that was taken can be used in an M4 or M16 assault rifle.