Following the outbreak of the Civil War, Hatch was ordered to the East and assigned to the cavalry of George B. McClellan. He was made a brigadier general of volunteers on September 28, 1861. In December, he was assigned command of a brigade of cavalry stationed at Annapolis, Maryland, serving under General Rufus King. Hatch's brigade made a series of daring raids on enemy positions near the Rapidan and Rappahannock rivers. These raids gained his brigade the Nickname Iron Brigade, which followed that brigade up until January 1863, long after Hatch had moved on.
