Hill resigned from the military in March 1861 and joined the Confederacy. He entered the Civil War as a colonel in command of the 13th Virginia Infantry. Hill’s regiment was held in support during the early Confederate victory at the First Battle of Bull Run (Manassas) in July 1861, and he was later promoted to brigadier general in February 1862. Hill next served during the Peninsula Campaign, in which Union General George McClellan—Hill’s former West Point roommate—attempted to land his army on the Virginia coast and move on Richmond. Hill performed well in the early stages of the invasion, and was noted for his aggressive performance at the Battle of Williamsburg in May 1862. He earned his second major promotion in three months—to the rank of major general—shortly thereafter.
Even though it was one of largest divisions in the Confederate Army, Hill christened his new command the Light Division—likely due to the breakneck pace at which he moved his troops. Hill’s reputation as a fearless commander continued to grow during the Seven Days Battles in June 1862; he was noted for riding near the front of his lines during the Battle of Beaver Dam Creek. During this time Hill also engaged in public arguments with his commander, General James Longstreet, over a series of newspaper articles that inflated Hill’s role in the Battle of Glendale. The feud reached a boiling point when Longstreet placed Hill under arrest for insubordination. With the possibility of a duel looming, in July 1862 Robert E. Lee transferred Hill and his Light Division to General Thomas “Stonewall” Jackson’s Army of the Shenandoah.
Hill quickly proved valuable in his new command, participating in a successful counterattack during the Battle of Cedar Mountain in August 1862. He later played a key defensive role in the Second Battle of Bull Run (Second Manassas), in which his troops thwarted repeated Union attacks. Despite these strong early results, Hill clashed with Jackson over marching orders during the Maryland Campaign and was placed under arrest for neglect of duty. He was soon reinstated, however, and performed admirably during the Battle of Antietam in September 1862. Hill’s fleet-footed Light Division proved invaluable during the bloody engagement, undertaking a force march from Harpers Ferry to the battlefield at a blistering pace. Arriving at a crucial time in the engagement, Hill was able to reinforce Lee’s army and repel the forces of General Ambrose Burnside.
Hill next served during the overwhelming Confederate victory at the Battle of Fredericksburg in December 1862. His actions during the battle proved controversial, as his was the only Confederate line breached by a Union charge, requiring an emergency counterattack from forces under the command of General Jubal Early. At the Battle of Chancellorsville in May 1863, Hill briefly took command of Jackson’s Second Corps after Jackson was mortally wounded. Hill was then forced to turn command over to General J.E.B. Stuart after being wounded in his calves by a musket shot.