Sherman proceeded to invade the state of Georgia with three armies: the 60,000-strong Army of the Cumberland under George Henry Thomas, the 25,000-strong Army of the Tennessee under James B. McPherson, and the 13,000-strong Army of the Ohio under John M. Schofield. He commanded a lengthy campaign of maneuver through mountainous terrain against Confederate General Joseph E. Johnston's Army of Tennessee, attempting a direct assault only at the Battle of Kennesaw Mountain. In July, the cautious Johnston was replaced by the more aggressive John Bell Hood, who played to Sherman's strength by challenging him to direct battles on open ground. Meanwhile, in August, Sherman "learned that I had been commissioned a major-general in the regular army, which was unexpected, and not desired until successful in the capture of Atlanta".