[1]: 6–12 Burns was stationed at Fort Smith, Arkansas, when the war began, narrowly avoiding capture when that place fell to Confederate militia forces on April 23, 1861.

Burns served in that capacity during McClellan's successful campaign in western Virginia that summer, and was promoted to the Regular Army rank of major in August 1861.

He led the brigade in a pivotal role at the battle of Savage Station (June 29), a rear-guard action fought to protect the Army of the Potomac as it retreated from Richmond.

Despite receiving a painful facial wound, Burns and his brigade successfully drove off a Confederate attack and allowed the Union withdrawal to continue without interference.

Perhaps his greatest contribution to history occurred earlier in the campaign; during the battle of Fair Oaks (May 31), Burns had ordered his men to assist an artillery battery that had gotten stuck on a rickety plank bridge over a flooded river.

Burns's men helped move the cannon off the bridge and through the mud on the other side, allowing the battery to be in place in time to play a significant role in driving off the last Confederate attack of the day.

Even more importantly, a shot fired by that battery severely wounded Confederate General Joseph E. Johnston, who was replaced after the battle by Robert E.