Adam Badeau, Military history of Ulysses S. Grant from April 1861 to April 1865. Volume 1

[479] be seen, and their numbers estimated, by the enemy; but, as soon as they passed in rear of the hills, Bragg must be at a loss to know whether they were moving to Knoxville, or were held on the north side of the river, for further operations at Chattanooga. It was also known that the north end of Missionary ridge was imperfectly guarded; and, that the left bank of the Tennessee, from the mouth of South Chickamauga creek westward, to the main rebel line in front of Chattanooga, was watched by a small cavalry picket only. These facts determined Grant's plan of operations. As his main object was to mass all the forces possible against Missionary ridge, converging towards its northern end, which covered Chickamauga station, Bragg's depot of supplies, Grant finally deemed it best to countermand Hooker's attack on Lookout mountain, and bring most of the troops intended for that operation, to the other end of the line.

The instructions to Thomas were in these words:

All preparations should be made for attacking the enemy's position on Missionary ridge, by Saturday morning, at daylight. . . . . The general plan is for Sherman, with the force brought with him, strengthened by a division from your command, to effect a crossing of the Tennessee river, just below the mouth of the Chickamauga; his crossing to be protected by artillery from the heights of the north bank of the river (to be located by your chief of artillery), and to secure the heights (Missionary ridge) from the northern extremity to about the railroad tunnel, before the enemy can concentrate against him. You will cooperate with Sherman. The troops in Chattanooga valley should all be concentrated on your left flank, leaving only the necessary force to defend fortifications