Chattanooga is on the south bank of the Tennessee, where that river runs nearly due west.  It is at the northern end of a valley five or six miles in width, through which Chattanooga Creek runs.  To the east of the valley is Missionary Ridge, rising from five to eight hundred feet above the creek and terminating somewhat abruptly a half mile or more before reaching the Tennessee.  On the west of the valley is Lookout Mountain, twenty-two hundred feet above-tide water.  Just below the town the Tennessee makes a turn to the south and runs to the base of Lookout Mountain, leaving no level ground between the mountain and river.  The Memphis and Charleston Railroad passes this point, where the mountain stands nearly perpendicular.  East of Missionary Ridge flows the South Chickamauga River; west of Lookout Mountain is Lookout Creek; and west of that, Raccoon Mountains.  Lookout Mountain, at its northern end, rises almost perpendicularly for some distance, then breaks off in a gentle slope of cultivated fields to near the summit, where it ends in a palisade thirty or more feet in height.  On the gently sloping ground, between the upper and lower palisades, there is a single farmhouse, which is reached by a wagon-road from the valley east.

The intrenched line of the enemy commenced on the north end of Missionary Ridge and extended along the crest for some distance south, thence across Chattanooga valley to Lookout Mountain.  Lookout Mountain was also fortified and held by the enemy, who also kept troops in Lookout valley west, and on Raccoon Mountain, with pickets extending down the river so as to command the road on the north bank and render it useless to us.  In addition to this there was an intrenched line in Chattanooga valley extending from the river east of the town to Lookout Mountain, to make the investment complete.  Besides the fortifications on Mission Ridge, there was a line at the base of the hill, with occasional spurs of rifle-pits half-way up the front.  The enemy’s pickets extended out into the valley towards the town, so far that the pickets of the two armies could converse.  At one point they were separated only by the narrow creek which gives its name to the valley and town, and from which both sides drew water.  The Union lines were shorter than those of the enemy.

Thus the enemy, with a vastly superior force, was strongly fortified to the east, south, and west, and commanded the river below.  Practically, the Army of the Cumberland was besieged.  The enemy had stopped with his cavalry north of the river the passing of a train loaded with ammunition and medical supplies.  The Union army was short of both, not having ammunition enough for a day’s fighting.

General Halleck had, long before my coming into this new field, ordered parts of the 11th and 12th corps, commanded respectively by Generals Howard and Slocum, Hooker in command of the whole, from the Army of the Potomac to reinforce Rosecrans.  It would have been folly to send them to Chattanooga to help eat up the few rations left there.  They were consequently left on the railroad, where supplies could be brought to them.  Before my arrival, Thomas ordered their concentration at Bridgeport.