Friday, June 27, 1862
Confederate General Robert E. Lee, undaunted by the previous day's events, attacked General Fitz-John Porter's Fifth Corps once again. Porter had repositioned his line from east to west on the north side of the Chickahominy River, near Gaines Mill. Union Commanding General George McClellan ordered Porter to hold his position at all costs.
Lee again ordered General Thomas "Stonewall" Jackson's division to attack Porter's Fifth Corps, with subsequent attacks by Generals Ambrose Powell Hill, Daniel Harvey Hill, and James Longstreet. For the second time in two days Jackson's division arrived late, and D.H. Hill's division went in to attack, with James Longstreet's division maneuvering for diversion. General Porter's line was reinforced, and the first series of attacks were repulsed. The Confederates resumed the attacks after nightfall and broke Porter's line.
The Confederate breakthrough at Gaines Mills convinced General George McClellan that he must remove the Army of the Potomac from their current position near Richmond to Harrison's Landing on the James River. He was certain that the Confederates outnumbered his forces more than two to one, which was entirely false. The Union forces had the greater strength in numbers. McClellan was unnerved by Lee's aggressiveness and surrendered the offensive initiative.
The Twentieth Massachusetts Regiment, remaining in position behind fortifications near Fair Oaks, was not engaged at Gaines Mill. Their time away from battle was about to change abruptly.1
1George A. Bruce, The Twentieth Regiment of Massachusetts Volunteer Infantry 1861 - 1865 (Cambridge, Massachusetts: The Riverside Press, 1906), 108-9. Richard F. Miller, Harvard's Civil War: A History of the Twentieth Massachusetts Volunteer Infantry (Lebanon, New Hampshire: University Press of New England, 2005), 137-38.