York militia as a captain. Shortly after the fall of Fort Sumter, Butterfield joined the Clay Guards of Washington, D.C. as a first sergeant, but subsequently transferred to the 12th New York Volunteer Infantry as a colonel. He was commissioned brigadier and major general of the Volunteers and commanded a division of the V Corps. He fought at the First Battle of Bull Run on 21 July 1861. He wrote the 1862 Army field manual, Camp and Outpost Duty for Infantry. Butterfield joined Maj. Gen. George B. McClellan's Army of the Potomac for the Peninsula Campaign in the V Corps, commanded by Maj. Gen. Fitz John Porter. In the Seven Days Battles, at Gaines' Mill on June 27, 1862, he was wounded but demonstrated the bravery that was eventually recognized in 1892, with the Medal of Honor. Butterfield continued in brigade command at the Second Battle of Bull Run and the Battle of Antietam, became division commander and then V Corps commander for the Battle of Fredericksburg. His corps was one of those assaulting through the city before facing an assault from Marye's Heights. After the debacles of Fredericksburg and the Mud March, Maj. Gen. Joseph Hooker replaced Ambrose Burnside as Army of the Potomac commander and Butterfield became Hooker's chief of staff in January 1863. Butterfield was promoted to major general of volunteers in March 1863, with a date of rank of November 29, 1862. Hooker and Butterfield developed a close personal and political relationship. To the disgust of many army generals, their headquarters were frequented by women and liquor, being described as a combination of a "bar and brothel". Political infighting became rampant in the high command and Butterfield was widely disliked by most of his colleagues. However, in the spring of 1863, the two officers managed to turn around the poor morale of the army and greatly improved food, shelter and medical support. During this period Butterfield introduced another custom that remains in the Army today: the use of distinctive hat or shoulder patches to denote the unit to which a soldier belongs, in this case the corps. He was inspired by the division patches used earlier by Maj. Gen. Philip Kearny, but extended those to the full army; Butterfield designed most of the patches himself. Hooker was replaced after the Battle of Chancellorsville by Maj. Gen. George G. Meade, just before the Battle of Gettysburg. Meade