Army of the Mississippi
In 1863 Maj. Gen. John A. McClernand was put in command of the expedition against down the Mississippi. He was given command of two corps from the Army of the Tennessee, his own XIII Corps led by Brig. Gen. George W. Morgan and Maj. Gen. William T. Sherman's XV Corps. McClernand named his force the "Army of the Mississippi" and redesignated the XIII Corps the I Corps, Army of the Mississippi, and the XV Corps became the II Corps, Army of the Mississippi. McClernand was successful in capturing Arkansas Post. Maj. Gen. Ulysses S. Grant did not like McClernand and after Sherman and Admiral Andrew H. Foote both voiced their opinions that McClernand was unfit to command, Grant personally took command of the expedition against Vicksburg and the old XIII Corps and XV Corps were returned to the Army of the Tennessee on January 12, 1863.