There were five corps in the Union Army designated as II Corps (Second Army Corps) during the American Civil War. These formations were the Army of the Cumberland II Corps commanded by Thomas L. Crittenden from October 24, 1862, to November 5, 1862, later renumbered XXI Corps; the Army of the Mississippi II corps led by William T. Sherman from January 4, 1863, to January 12, 1863, renumbered XV Corps; Army of the Ohio II Corps commanded by Thomas L. Crittenden from September 29, 1862, to October 24, 1862, transferred to Army of the Cumberland; Army of Virginia II Corps led by Nathaniel P. Banks from June 26, 1862, to September 4, 1862, and Alpheus S. Williams from September 4, 1862, to September 12, 1862, renumbered XII Corps; and the Army of the Potomac II Corps from March 13, 1862, to June 28, 1865.
Of these five, the one most widely known was the Army of the Potomac formation, the subject of this article.
Corps history
The II Corps was prominent by reason of its longer and continuous service, larger organization, hardest fighting, and greatest number of casualties. Within its ranks was the regiment that sustained the largest percentage of loss in any one action; the regiment that sustained the greatest numerical loss in any one action; and the regiment that sustained the greatest numerical loss during its term of service. Of the one hundred regiments in the Union Army that lost the most men in battle, thirty-five of them belonged to the II Corps. The II Corps also fought in nearly every battle in the main Eastern Theater, from the 1862 Peninsula Campaign to the Confederate surrender at Appomattox Court House.
The corps was organized under General Orders No. 101, March 21, 1862, which assigned Brigadier General Edwin Vose Sumner to its command, and Brigadier Generals Israel B. Richardson, John Sedgwick, and Louis Blenker to the command of its divisions. Within three weeks of its organization the corps moved with George B. McClellan's Army of the Potomac on the Peninsula Campaign, except for Blenker's division, which was withdrawn on March 31 from McClellan's command, and ordered to reinforce John C. Frémont's army in western Virginia. Blenker's division never rejoined the corps. The remaining two divisions numbered 21,500 men, of whom 18,000 were present for duty.
The first general engagement of the corps occurred at the Battle of Seven Pines, where Sumner's prompt and soldierly action brought the corps on the field in time to retrieve a serious disaster, and change a rout into a victory. In a fierce engagement with Confederate general Gustavus W. Smith's division, Brig. Gen Oliver Howard was shot in the arm and had to have it amputated, causing him to miss all of the summer campaigning of the army. The casualties of the two divisions in that battle amounted to 196 killed, 899 wounded, and 90 missing. In the Seven Days Battles, the II Corps was not engaged until Savage's Station when it held off Confederate general John B. Magruder's troops. The following day, the corps was engaged at Glendale, where John Sedgwick's division was in the thick of the fighting. Israel Richardson's division spent the battle to the north engaged in a standoff with "Stonewall" Jackson's troops on opposite sides of White Oak Swamp; fighting here was limited to artillery dueling. The corps was held in reserve at Malvern Hill. Total II Corps casualties in the Seven Days were 201 killed, 1,195 wounded, and 1,024 missing. Afterwards, Sumner, Sedgwick, and Richardson all received promotions to major general as part of a blanket promotion of each corps and division commander in the Army of the Potomac. The II Corps spent the Northern Virginia Campaign in Washington, D.C., and did not participate in it except at the very end when it moved out to cover the retreat of Maj. Gen John Pope's army.