What is the significance of the battle of lookout mountain?

It was the second action in the battle of Chattanooga and was significant because Gen. Braxton Bragg unexpectedly lost the key position south of the city, called Lookout Mountain, when Union Gen. Hooker succeeded in seizing the top of the mountain opening the first breach in the Confederate defensive system.

Bragg was therefore forced to withdraw his left wing behind the Chattanooga Creek.