The 4th Cavalry Brigade is an AC/RC unit based at Fort Knox, Kentucky. The unit is responsible for training selected United States Army Reserve & National Guard units that are based East of the Mississippi River. The brigade was originally formed as an element of the 2nd Cavalry Division but was inactivated after the division was broken up. The unit was formerly designated as 4th Brigade, 85th Division. The brigade is a subordinate unit of 1st Army