Rosecrans’ feigned move on the western end of the Confederate line had left the eastern mountain passes lightly defended, and Colonel John T. Wilder's mounted infantry achieved total surprise when they attacked Hoover's Gap.

Success was attributed both to Rosecrans’ brilliant deception tactics and the high morale of Wilder’s "Lightning Brigade", equipped with the new Spencer repeating rifle.

Following the Battle of Stones River, Maj. Gen. William Rosecrans, commanding the Union Army of the Cumberland, remained in the Murfreesboro, Tennessee, area for over five months.

In an effort to block further Union progress, Confederate Gen. Braxton Bragg, commander of the Army of Tennessee, established a fortified line along the Duck River from Shelbyville to Wartrace.

On the Confederate right, infantry and artillery detachments guarded Liberty, Hoover's, and Bellbuckle Gaps through the Highland Rim (near Beechgrove, Tennessee).

Rosecrans's superiors, fearing that Bragg might detach large numbers of men to help break the Siege of Vicksburg, urged him to attack the Confederate positions.

Having witnessed a demonstration of a new repeating rifle by Christopher Miner Spencer in March, Wilder determined to arm his brigade with that weapon.

[4] As Butler's unit fell back the entire 7 mi (11 km) mile length of Hoover's Gap, it ran into Brig.

[4] Although slowed by rain, Rosecrans moved on, forcing Bragg to retreat from his defensive line and fall back to Tullahoma.