Sherman began his Atlanta Campaign on May 4. Johnston's Army of Tennessee fought defensive battles against the Federals at the approaches to Dalton, which was evacuated on May 13, then retreated 12 miles south to Resaca, and constructed defensive positions. However, after a brief battle, Johnston again yielded to Sherman, and retreated from Resaca on May 15. Johnston assembled the Confederate forces for an attack at Cassville. As his troops advanced, an enemy force of unknown strength appeared unexpectedly on his right flank. A skirmish ensued, forcing the corps commander, Lt. Gen. John Bell Hood, to halt his advance and reposition his troops to face the threat. Faced with this unexpected threat, Johnston abandoned his attack and renewed his retreat. On May 20 they again retreated 8 miles further south to Cartersville. The month of May 1864 ended with Sherman's forces attempting to move away from their railroad supply line with another turning movement, but became bogged down by the Confederates' fierce defenses at the Battle of New Hope Church on May 25, the Battle of Pickett's Mill on May 27, and the Battle of Dallas on May 28.