At first, Garfield approved of Rosecrans' delay, but as soon as his army was thoroughly reinforced with men and supplies, he urged him to make an advance. Through the secret service system which he had established since Jordan's wonderful expedition, Garfield discovered that Bragg's army was greatly reduced, and he felt assured that the time had come for a decisive blow. At last, General Rosecrans sent a formal letter to his corps, division, and cavalry generals asking their opinion concerning the feasibility and wisdom of such a movement. Not one of the seventeen generals was in favor of an immediate or even an early advance. Garfield took the answers sent in from the generals, and in one of the ablest military documents on record,[A] he refuted every objection raised, and added therewith such powerful arguments in favor of an immediate advance, that General Rosecrans was convinced. Twelve days later, the army moved, much to the chagrin of the other officers, who declared it was a rash and fatal step for which Garfield alone should be held responsible. It was the opening of the famous Tullahoma campaign--a campaign remarkable throughout for its fine conception and able execution. Bragg's army would have been utterly destroyed had the advance been made a few days earlier; as it was, the rebel forces were finally driven south of the Tennessee, a thousand five hundred and seventy-five prisoners were captured, together with considerable ammunition, and the state of Tennessee was again under the flag of the Union. Almost on the boundary line between Tennessee and Georgia stands the village of Chattanooga. It is on the southern bank of the Tennessee river, and to the north Lookout Mountain rises almost perpendicularly to a height of twenty-four hundred feet. Missionary Ridge, which is a much lower elevation, lies upon the eastern side, and along its base flows the West Chickamauga Creek that empties into the Tennessee just at Chattanooga. On the opposite side is Pigeon Mountain. The Tullahoma campaign had forced Bragg and his remaining troops across the Tennessee, and they were now posted all along the southern bank of the stream from Chattanooga far down toward Atlanta. Rosecrans' army had encamped themselves on the west with a line of fortifications one hundred and fifty miles long, while General Burnside had moved into Eastern Tennessee, and taken possession of Knoxville. The great problem now was how to force Bragg from his position at Chattanooga. It was about this time that Rosecrans received a letter, in which a plan for arming the negroes and sending them throughout the slave states, was proposed. "It would doubtless end the rebellion at once," said one of Rosecrans' officers; "and the letter says that no blood would be shed except in self-defence." "But, think what vengeance the blacks might take, if suddenly let loose upon their masters!" exclaimed Rosecrans. "I must talk the matter over with Garfield."