Soon after Major General William S. Rosecrans assumed command of the first Union Army of the Ohio and changed its name to the Army of the Cumberland on October 24 1862 he took steps to increase the number of men in the four Regular Army regiments ( Carson's 15th and the 16th 18th and 19th U. S. Infantry Regiments ) under his command to their authorized strength and to place them in a single Regular Brigade .