It was at this time that I recommended to the general-in-chief the movement against Mobile.  I knew the peril the Army of the Cumberland was in, being depleted continually, not only by ordinary casualties, but also by having to detach troops to hold its constantly extending line over which to draw supplies, while the enemy in front was as constantly being strengthened.  Mobile was important to the enemy, and in the absence of a threatening force was guarded by little else than artillery.  If threatened by land and from the water at the same time the prize would fall easily, or troops would have to be sent to its defence.  Those troops would necessarily come from Bragg.  My judgment was overruled, and the troops under my command were dissipated over other parts of the country where it was thought they could render the most service.

Soon it was discovered in Washington that Rosecrans was in trouble and required assistance.  The emergency was now too immediate to allow us to give this assistance by making an attack in rear of Bragg upon Mobile.  It was therefore necessary to reinforce directly, and troops were sent from every available point.

Rosecrans had very skilfully manoeuvred Bragg south of the Tennessee River, and through and beyond Chattanooga.  If he had stopped and intrenched, and made himself strong there, all would have been right and the mistake of not moving earlier partially compensated.  But he pushed on, with his forces very much scattered, until Bragg’s troops from Mississippi began to join him.  Then Bragg took the initiative.  Rosecrans had to fall back in turn, and was able to get his army together at Chickamauga, some miles south-east of Chattanooga, before the main battle was brought on.  The battle was fought on the 19th and 20th of September, and Rosecrans was badly defeated, with a heavy loss in artillery and some sixteen thousand men killed, wounded and captured.  The corps under Major-General George H. Thomas stood its ground, while Rosecrans, with Crittenden and McCook, returned to Chattanooga.  Thomas returned also, but later, and with his troops in good order.  Bragg followed and took possession of Missionary Ridge, overlooking Chattanooga.  He also occupied Lookout Mountain, west of the town, which Rosecrans had abandoned, and with it his control of the river and the river road as far back as Bridgeport.  The National troops were now strongly intrenched in Chattanooga Valley, with the Tennessee River behind them and the enemy occupying commanding heights to the east and west, with a strong line across the valley from mountain to mountain, and with Chattanooga Creek, for a large part of the way, in front of their line.

On the 29th Halleck telegraphed me the above results, and directed all the forces that could be spared from my department to be sent to Rosecrans.  Long before this dispatch was received Sherman was on his way, and McPherson was moving east with most of the garrison of Vicksburg.