"...regarded the fighting of late March and much of April 1915 as possibly the most savage along the Inner Line in the entire campaign. While both sides did their best to rotate fresh troops into the defensive trenches, it remained the case that many of the divisions brought off the immediate first line were kept nearby, with Confederates typically getting a mere two weeks leave in nearby Murfreesboro rather than back home, for fear that they might otherwise desert. Conditions in Nashville had gotten bleaker and bleaker, too; the Yankees had brought in specially-built long-range artillery that was meant not for precision but to randomly lob high-explosive shells or chlorine gas canisters behind the Inner Line for psychological purposes, with the risk that they could land anywhere; sometimes, spent shell casings were fired into Nashville just to flatten whatever they landed on and to demonstrate that nowhere behind the defenses was safe. Nashville was closer to a ghost town than a city, with perhaps as much as ninety percent of her prewar free population having been evacuated; slaves were seized by the Army and put to tasks of war, often dealing with sorting through dead bodies to identify them and prepare them for burial.
Something had to break eventually, and the break came on April 26th when the Inner Line finally showed her first crack at Gallatin, about forty kilometers northeast of the Tennessee State House and roughly halfway between the smaller industrial towns of Hendersonville and Hartsville. The wooded hills of the Highland Rim had by April of 1915 been reduced to little more than dead gray no man's land, pockmarked with impact craters, studded with the smoldering black stumps of what once were trees and littered with the occasional corpse that one of the combatants had been unable to safely collect. The destruction of the area's tree cover had, of course, made it much easier to identify from high ground and airplane the weak points in the Confederate line, and Farnsworth, mere days before he was to be cycled back and relieved of command, had deduced that the relatively low hills just north of Gallatin were the weak link in the Inner Line's chain of earthworks, minefields and pillboxes supporting the multiple layers of trenches.
Therefore, on the early morning of April 26th, an unholy artillery fair rained down on this segment of the Line, known as Section D-IV in Yankee planning maps, followed by a thrust straight through it by three Hellfighter regiments that managed to do what no offensive into the maw of the Line had done yet - punch their way through and onto the other side. Despite sustaining grievous casualties, the Hellfighters cracked the defenses at what was once the hamlet of Graball and before they knew it were on the road to Gallatin, with two corps under Lenihan directly to their rear. Lenihan's famed aggressiveness and thirst for high-paced offensives had made him the natural choice to lead American forces into the Battle of Gallatin; that he wanted to seize Nashville before he got sent to Virginia in mid-May to satisfy his ego certainly had something to do with the matter, too. By late in the day on the 27th, Lenihan could see the rooftops of Gallatin, less than two kilometers away; on the 28th, his men fought their way in.
The capture of Gallatin was a disaster for the Confederacy. Not only did it place American troops behind the Inner Line for the first time, it cut off the most direct route along the southern slopes of the Highland Rim to the eastern anchor of the Line in Hartsville, forcing Buck's supplies and men to instead be routed via Lebanon, south of the Cumberland. It gave Lenihan and the troops streaming in behind him once he sent word of his successful breakthrough all of the operational initiative - they could backfill their left flank and march on Hendersonville along the right bank of the Cumberland towards Nashville, they could hold fast and allow reinforcements to swing east and capture Hartsville, or they could cross the Cumberland and continue their effort to cut the Confederate logistics network in half by threatening Lebanon. Unless they were repulsed, and soon, Nashville would collapse.
Buck pulled regiment after regiment off their defenses in the Line to be marched into the eastern sector of the operational theater, electing to concentrate a corps in Hartsville and two in Lebanon; he did this under mobile light artillery fire brought into the "breach" at Graball that could penetrate deep into the Nashville Basin and strafing from airplanes, most lethally the new C-6 model from Curtiss-Wright Company which had built long guns into the fuselage to eliminate the need of a gunner, guns that fired 20mm ammunition rounds (a limited number, of course) and thus allowed for maximum destruction upon dive runs. Harried under this breaking fire, Buck's attempt to arrest the attempted breakout by Lenihan was considerably slowed.
Aware from reconnaissance where Buck was trying to meet him, Lenihan elected to draw Confederate defenses further from central Nashville and on April 30th crossed the Cumberland; on the morning of the 1st, both of his corps as well as two regiments of Hellfighters were successfully across, with an additional two corps now having plugged the gap behind him to defend his rear and prevent an attack from either Hartsville or Hendersonville. The Confederate position was, quite simply, in total collapse..."
- Bleeding Heartland: The Midlands Front of the Great American War
