Gen. Ulysses S. Grant, newly promoted to be general-in-chief of all the Union armies, summoned Sheridan to the Eastern Theater to command the Cavalry Corps of the Army of the Potomac. Unbeknownst to Sheridan, he was actually Grant's second choice, after Maj. Gen. William B. Franklin, but Grant agreed to a suggestion about Sheridan from Chief of Staff Henry W. Halleck. After the war, and in his memoirs, Grant claimed that Sheridan was the very man he wanted for the job. Sheridan arrived at the headquarters of the Army of the Potomac on April 5, 1864, less than a month before the start of Grant's massive Overland Campaign against Robert E. Lee.