What kind of Union occupation force remained in Chattanooga after Atlanta was abandoned? Were they occupying the defenses built by the AotC in 1863?
In Chattanooga? I would assume so. During the old Chattanooga Campaign, Rosecrans took two regiments and formed them into a temporary brigade to garrison the city -- these troops never left. Originally just the 44th Indiana and 15th Kentucky, they were soon joined by the 8th Kentucky, 15th Wisconsin, and the 15th, 29th, and 32nd Indiana. During the Atlanta Campaign, Chattanooga became a staging area for Sherman's armies: all reinforcements passed through the city at one time or another. To spare veteran troops hard fighting right before muster-out, several regiments were detached from the AotC and AotT a few months before their time expired, and sent to garrison Chattanooga and other points along that road. The original garrison regiments remained where they were, and the field-worthy batteries of the Army of the Cumberland/Army of the Tennessee Artillery Reserves were transferred from Nashville and Memphis, respectively, to Chattanooga, where they formed an artillery corps under Colonel James Barnett.
After the Atlanta Campaign, the Western Regular Brigade was so reduced in numbers that it was detached from the Fourteenth Corps and sent to Chattanooga. Until the end of the war, the Regulars camped on and picketed Lookout Mountain. But during Sherman's March, Sherman ordered the collection of all miscellaneous men at Chattanooga. All men who had straggled, been on sick leave, veteran furlough, new recruits,
from Sherman's army were to be collected at Chattanooga. By December, 1864, roughly 6,000 men had reached the rendezvouses at the camp, and were organized into two divisions -- one under Brig. Gen. Charles Cruft and another under famed Brig. Gen. Thomas F. Meagher. As it was December, 1864, Cruft's division (the only one fully organized, if you could call it that) was immediately sent to Nashville under District commander Steedman's command. Meagher's division continued organizing at Chattanooga. Before leaving, Steedman had worried about Confederate attacks coming from Atlanta, and had placed a reinforced regiment at Dalton under Colonel Joshua B. Culver. (It wasn't Culver's 13th Michigan, since Culver was one of the miscellaneous officers from Sherman's army -- his regiment was at Savannah.)
After the Battle of Nashville, Cruft's division returned to Chattanooga. The provisional troops (all the aforementioned detritus) were ordered to Sherman, and departed for North Carolina under Meagher's command. They would fight as the composite units they were at the Battle of Wyse Fork. Cruft remained behind with the original Garrison Brigade, the Regulars, and the Reserve Artillery. That month, and in early 1865, the states of Illinois, Indiana, and Ohio organized a combined total of over sixty new regiments. Roughly a quarter of these were sent to Chattanooga, and by April, 1865, the forces in Chattanooga constituted two divisions of three brigades each, half of which were new troops. The garrison had grown so large that the District of the Etowah could finally expand, and brigades regarrisoned Dalton and other points closer to Atlanta.
At the very end of the war, the garrison of Chattanooga consisted of the remaining members of the former Garrison Brigade: the 29th, 32nd, and 44th Indiana, along with the 68th Indiana and a composite unit, the 18th Ohio Veterans. The Regulars still garrisoned Lookout, and the Artillery Reserve under Maj. John Mendenhall camped outside the city. A brigade of USCT, most of whom had fought at Nashville, also guarded the city.
HTHs