During Maj. Gen. William Tecumseh Sherman's advance through Georgia in the spring of 1864, the Army of the Cumberland numbered over 60,000 men, and Thomas's staff did the logistics and engineering for Sherman's entire army group, including developing a novel series of Cumberland pontoons. At the Battle of Peachtree Creek (July 20, 1864), Thomas's defense severely damaged Lt. Gen. John B. Hood's army in its first attempt to break the siege of Atlanta.