Battle of Gaines's Mill - Background

Background

McClellan's Army of the Potomac had pushed to within a few miles of the Confederate capital of Richmond and had stalled following the Battle of Seven Pines in late May 1862. Lee wanted to take the initiative, believing that remaining on the strategic defensive would play into Union hands and allow the Confederacy to be worn down. He planned to shift his 90,000-man Confederate army to the north of Richmond, and attack McClellan's right flank. The Confederate cavalry under the command of Maj. Gen. J.E.B. Stuart had ridden around McClellan's army, confirming that the flank was open—not anchored on Totopotomoy Creek—and vulnerable. Lee planned to use Maj. Gen. Stonewall Jackson's force, transported by rail from the Shenandoah Valley, to attack on McClellan's right and rear, while the remainder of his army under Maj. Gens. A.P. Hill, James Longstreet, and D.H. Hill attacked from the direction of Mechanicsville.

The Seven Days Battles began with a Union attack in the minor Battle of Oak Grove on June 25, but the first major battle started the next day when Lee launched a large-scale assault against McClellan at the Battle of Beaver Dam Creek (or Mechanicsville). Lee attacked Porter's V Corps north of the Chickahominy, while the bulk of the Union Army was relatively unoccupied south of the river. Although this battle was a tactical victory for the Union, McClellan realized that he could not keep Porter's corps in place with Jackson threatening his flank. He ordered Porter to begin a withdrawal and at the same time decided to change the army's base of supply from White House on the Pamunkey River to Harrison's Landing on the James River. (This decision was fatal to McClellan's campaign because by abandoning the railroad that led from the Pamunkey, he would no longer be able to supply his planned siege of Richmond with the necessary heavy artillery.)

Several of McClellan's subordinates urged him to attack the Confederate division of Maj. Gen. John B. Magruder south of the Chickahominy, but he feared the vast numbers of Confederates he believed to be before him and failed to capitalize on the overwhelming superiority he actually held on that front. Magruder assisted in this misapprehension by ordering frequent, noisy movements of small units back and forth and by using groups of slaves with drums to simulate large marching columns. Furthermore, the Union Army Balloon Corps, which had performed the only aerial observation during the Peninsula Campaign, was now joined by a Confederate competitor. Capt. Langdon Cheves of South Carolina had constructed a multicolored balloon of dress silk obtained from Charleston and Savannah, which sailed aloft tethered to a boxcar on the York River Railroad, manned by Maj. Edward Porter Alexander. The appearance of this balloon reinforced McClellan's fear that the Confederates were planning for an offensive against his left flank. For the second day, the Confederates were able to continue fooling McClellan south of the river by employing minor diversionary attacks to command the attention of 60,000 Federal troops while the heavier action occurred north of the river.

The order to Porter's corps came just before dawn and they did not have adequate time to prepare a strong rear guard for the withdrawal, resulting in numerous men from Brig. Gen. George A. McCall's division being captured by the advancing Confederates. Porter selected a new defensive line on a plateau behind Boatswain's Swamp, just to the southeast of a mill owned by Dr. William F. Gaines. It was a strong position, with two divisions laid out in a semicircle—Brig. Gen. George W. Morell on the left and Brig. Gen. George Sykes on the right—and two divisions in reserve—Brig. Gen. George A. McCall and Brig. Gen. Henry W. Slocum, the latter on loan to Porter from Brig. Gen. William B. Franklin's VI Corps. Slocum's division had not crossed the river by the start of the battle, held up by McClellan's concern about an impending attack on Franklin's front.

Lee's offensive plan for June 27 was similar to that of the preceding day. He would use A.P. Hill's and Longstreet's divisions to pressure Porter's corps as it withdrew, while Stonewall Jackson, augmented by D.H. Hill (Jackson's brother-in-law), hit Porter's right and rear. The combined effort of all of Lee's force was destined to be the largest Confederate attack of the war, about 57,000 men in six divisions. Lee traveled to Walnut Grove Church to meet with Jackson and describe the plan, which called for Jackson to march toward Old Cold Harbor, and then south beyond Porter's flank. Unfortunately, Lee made incorrect assumptions about Porter's disposition. He assumed that the V Corps would defend the line of Powhite Creek, somewhat to the west of Porter's actual location.