 On November 7 , 1862 , Maj. Gen. McClellan was removed from command of the Army of the Potomac and replaced with Maj. Gen. Burnside . Over the course of November , Burnside moved the army south to Falmouth , Virginia , opposite the Rappahannock River from Fredericksburg . The 21st arrived in Falmouth on November 19 . Nearly a month passed before Burnside could organize a crossing of the river and an assault on the city and the heights beyond . The Battle of Fredericksburg took place on December 13 , 1862 . 
