On August 16, 1863, Rosecrans moved his Federal army out from the Cumberland Plateau to the Tennessee River.  He intended to engage and defeat Bragg’s Confederates.

Map of Federal moves Bragg’s move in his battle report

Within a week of moving out the Feds were at the Tennessee River, and now needed the Bridgeport crossing rebuilt. [I have added a section of photos on the 1999 re-enactment of the battle of Bridgeport.] The river is very wide at this point and Rosecrans could not risk an opposed crossing, so deception would be the order of the day.  Crittenden had men, under Colonel Wilder, on the river above Chattanooga causing a diversion as if they were preparing a crossing, while artillery was placed on Stringer’s Ridge opposite Chattanooga to bombard the city. He wanted Bragg to believe that he would cross Walden Ridge and link up with Burnside from Knoxville.

Sheridan’s men built a bridge over the river at Bridgeport while other supplies were ferried over at Shellmound and Caperton’s Ferry. Using these routes Rosecrans had most of his army over the Tennessee River by September 4, this included all his artillery and ammunition sufficient for two large battles, also rations for more than three full weeks, if needed.  By September the 9th he had occupied Chattanooga, the day that Bragg evacuated the city.

Bragg had been taken in by the feints up-river, but it was his poor intelligence gathering that allowed him to be largely unaware of what was happening downstream where the Feds were making their crossings.  On August 31st he was told by a citizen of the Caperton’s Ferry area that Rosecrans was making a crossing, but he refused to believe this ‘unofficial’ intelligence source.  While Bragg was deciding his next move the Federals were climbing Lookout Mountain by the rough tracks, and on the 7th September Bragg decided he had to leave Chattanooga and move south to LaFayette where he would cover his communications and defeat the Union forces as they came out of their various mountain passes.

The following is from Bragg’s post battle report.

The nature of the country and the want of supplies in it, with the presence of Burnside's force on our right, rendered a movement on the enemy's rear with our inferior force extremely hazardous, if not impracticable. It was therefore determined to meet him in front whenever he should emerge from the   mountain gorges. To do this and hold Chattanooga was impossible without such a division of our small force as to endanger both parts. Accordingly our troops were put in motion on September 7 and 8, and took position from Lee and Gordon's Mills to La Fayette, on the road leading south from Chattanooga and fronting the east slope of Lookout Mountain

Rosecrans’ comment on Bragg leaving Chattanooga, from post battle report.

The reconnaissance of General Crittenden on the 9th developed the fact that  the enemy had evacuated Chattanooga the day and night previous and his advance took peaceable possession at 1 p.m.

At 10am on the 9th September Rosecrans dictated an order to General Thomas (who was against pursuing Bragg and preferred that the Federals should consolidate in Chattanooga) “The General commanding has ordered a general pursuit of the enemy by the whole army.  General Crittenden has started to occupy Chattanooga and pursue the line of Bragg’s retreat. .... General McCook has been ordered to move at once on Alpine and Summerville. The General commanding directs you to move your command as rapidly as possible to Lafayette and make every exertion to strike the enemy in flank, and if possible to cut off his escape.”

The orders for the three Union columns to take their routes were issued on the 9th September. By the 12th Rosecrans could see his mistake, the two wings of his army were more than 40 miles apart, and Bragg was concentrated against his centre under Thomas.

On the evening of the 9th September a Union force would be in action in McLemore’s Cove.