Babcock was part of XXIII Corps, and served under Union engineer Captain Orlando M. Poe. Poe and Union engineers, that included Babcock, built several fortifications in the form of bastioned earthworks near Knoxville. One was Fort Sanders, just west of downtown Knoxville across a creek valley. It was named for Brig. Gen. William P. Sanders, mortally wounded in a skirmish outside Knoxville on November 18, 1863. The fort, had an innovative design, and was a salient in the line of earthworks that surrounded three sides of the city, rose above the surrounding plateau and was protected by a ditch wide and deep. An almost insurmountable vertical wall rose above the ditch, slippery and frozen. Inside the fort were 12 cannons and 440 men of the 79th New York Infantry. In front of the ditch, telegraph wires were strung at knee height across tree stumps, possibly the first use of such wire entanglements in the Civil War, to entangle Confederate soldiers that would assault the Fort.