XIII Corps (Union Army)

XIII Corps was a corps of the Union Army during the American Civil War. It was first led by Ulysses S. Grant and later by John A. McClernand and Edward O.C. Ord. It served in the Western Theater of civil war, Trans-Mississippi Theater and along the Gulf of Mexico.

The XIII Corps, along with the XIV Corps, were both put into commission on October 24, 1862 with the passing of General Orders No. 168. These two corps were the first corps created in the Western Theater. While the XIV Corps constituted all forces under the command of William S. Rosecrans, the XIII Corps likewise constituted all the forces under Ulysses S. Grant.

Because of the corps' immense size and the fact that it was virtually synonymous with the Army of the Tennessee, Grant chose to subdivide the corps into the Right, Left and Center wings. In December 1862 it was officially divided into the XIII Corps, XV Corps, XVI Corps and XVII Corps. Grant remained in command of the Army of the Tennessee and John A. McClernand assumed command of the XIII Corps. Before the official order was passed along to all the wing commanders, William T. Sherman, commander of the Right Wing, embarked on an expedition against Vicksburg. Sherman's wing of the XIII Corps fought the Battle of Chickasaw Bayou on December 26–29. Although the official date which the Right Wing was designated the XV Corps was December 22, most of the reports regarding the battle at Chickasaw Bluffs still refer to the Union forces as part of the XIII Corps. No matter the designation, it was the first time many of the troops had been under fire.

Adding to the identity crisis the XIII Corps faced in its early years was John A. McClernand's expedition against Fort Hindman at Arkansas Post. McClernand was given his XIII Corps and Sherman's XV Corps (now officially using that designation). McClernand labeled these forces the Army of the Mississippi and renamed the XIII Corps "I Corps" and the XV Corps "II Corps". McClernand commanded the Army and placed General George W. Morgan in command of the I Corps (former XIII Corps). The divisions of Andrew J. Smith and Peter J. Osterhaus participated in the battle. Only Stephen Burbridge's brigade of Smith's division bore any heavy fighting.

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