The relationship between the phlegmatic Grant and the tempestuous Sherman has been beautifully detailed in Grant and Sherman: The Friendship That Won the Civil War. Biographer Charles Bracelen Flood shows how these two men—from such different backgrounds—became such good commanders and friends.

Sherman was two years older, and, by most accounts, much brighter than Grant, who for his part was much steadier (except when he was drunk). The two knew each other, faintly, from West Point, and their acquaintance turned to friendship in the campaign that terminated at the Battle of Shiloh. Throughout the Vicksburg campaign, Grant considered Sherman his irreplaceable second-in-command, and by the time he went to Chattanooga, Sherman was convinced that Grant was the greatest general in the war. At times, Sherman attempted to bolster his self-opinion; he wrote in his diary and in letters to his wife that Grant possessed only an average mind, while admitting that he had an uncanny ability to seek and obtain victory. Their friendship blossomed by the autumn of 1863 and would only become stronger in 1864.