Following the failures of the Peninsula campaign, Stoneman was reassigned to the infantry, and received command of the 1st Division of the III Corps on September 10 after its former commander, Maj. Gen. Phil Kearny, had been killed a week earlier. The III Corps remained in Washington, D.C., during the Maryland campaign. On October 30, Stoneman was placed in command of the entire III corps. At Fredericksburg, it formed part of Maj. Gen. Joseph Hooker's Center Grand Division and helped drive back a Confederate assault during the battle. Following Fredericksburg, Hooker became commander of the Army of the Potomac and decided to re-organize the cavalry into a single corps with Stoneman at its head.