Wednesday, June 25, 1862
Early in the morning Union General George McClellan began his attack on Richmond, hoping to seize the initiative against the Confederate Army before General Thomas "Stonewall" Jackson could deploy his forces as he relocated from the Shenandoah Valley. Union General Samuel Heintzelman's Third Corps attacked Confederate Major General Benjamin Huger's division between the Williamsburg and Charles City Roads in a dense forest near White Oak Swamp known as Oak Grove. In a battle that lasted all day the Union forces held the ground won, nearly four miles from Richmond. Oak Grove would prove to be the only encounter of the Seven Days Battles in which General McClellan took the offensive against General Robert E. Lee.
Most of General Napoleon Dana's brigade, which included the Twentieth Massachusetts Regiment, was not engaged at the Battle of Oak Grove. The Nineteenth Massachusetts Regiment was the only unit from Dana's brigade that took part in the battle, encountering a severe fight with the Confederates to secure the Union flank.1
1George A. Bruce, The Twentieth Regiment of Massachusetts Volunteer Infantry 1861 - 1865 (Cambridge, Massachusetts: The Riverside Press, 1906), 104-5. Richard F. Miller, Harvard's Civil War: A History of the Twentieth Massachusetts Volunteer Infantry (Lebanon, New Hampshire: University Press of New England, 2005), 136-37.