Was Chickamauga the bloodiest battle? The Gap in The Union Line at Chickamauga

Was Chickamauga the bloodiest battle? The Gap in The Union Line at Chickamauga

The week of September 15-21, 1863 would see the second bloodiest battle of the American Civil War!

US Civil War


Chickamauga Campaign, movements 10–12 September 1863.

The Battle of Chickamauga was the only authentic confederate victory in the western theater. When Maj Gen William Rosecrans moved to follow up on his almost bloodless tactical victory at Tullahoma, Confederate General Braxton Bragg abandoned Chattanooga.  Rosecrans divided up the army into three columns followed as Bragg went south, into the mountains of Georgia. 

Thinking Bragg was in full retreat, and wouldn’t stop until reaching Rome GA, Rosecrans pursued vigorously. Bragg had in fact concentrated his men at LaFayette, GA.  This location was near a railroad and he was expecting reinforcements to arrive. Also, this town was close to an isolated corps of Rosecrans’s army. When Bragg’s troops crossed Chickamauga Cree to attack, the Federals almost had an entire corps ambushed. Because of the mountainous and forest terrain, neither Bragg nor Rosecrans could ascertain precisely the location of the enemy, leading to many lost opportunities for flanking and attack.

The Battle 


Photograph of Lee and Gordon’s Mills near Chickamauga and Chattanooga National Military Park.

Rosecrans observed Bragg’s movement on September 18 so it was not the surprise Bragg had hoped. Reinforcements were sent to the vulnerable Union corps. The battle began in the morning of September 19. Bragg attacked through numerous fields and woods, but the Union defense held. Bragg’s men gain ground but cannot break the extended Union line despite a series of aggressive attacks. But on day 2, disaster struck. 

Bragg resumed his assault in the morning on the union left flank. He had been reinforced that evening by the arrival of Lt Gen James Longstreet and Hood’s division from the eastern heater after a long and circuitous route that took over a week to accomplish, and they were ordered into action. In the late morning, Rosecrans was under the impression that he had a gap in his line. In moving units to shore up the supposed gap, Rosecrans accidentally created an actual gap, directly in the path of an eight-brigade assault on a narrow front by Confederate Lt. Gen. James Longstreet. 

Gen. Braxton Bragg, CSA

Gen. Braxton Bragg, CSA

His corps was detached from the Army of Northern Virginia and arrived on the battlefield via a detour by railroad. In the resulting rout, Longstreet’s attack drove one-third of the Union army, including Rosecrans himself, from the field. Sheridan’s division made a gallant stand on Lytle Hill, but was swamped by retreating Union soldiers. The Confederates drove Sheridan’s division from the field in confusion. Union units spontaneously rallied to create a defensive line on Horseshoe Ridge (“Snodgrass Hill”), forming a new right wing for the line, and held until twilight. Union forces then retired to Chattanooga while the Confederates occupied the surrounding heights, besieging the city.

The Gap


Confederate troops advancing at Chickamauga (drawing by Alfred R. Waud)

The Confederate victory at Chickamauga was the consequence of this movement error ordered mistakenly by General Rosecrans.  It is commonly said that the gap developed because in the dense woods one of Rosecrans staff officers couldn’t detect the federal division that was actually in place, and reported incorrectly that a gap in the line existed.  This isn’t quite what correct; what happened is much more complicated.

Brig Gen John Brannan’s division was on the front line located between division commanded by Maj Gen Joseph Reynolds!

On his left and Brig Gen Thomas Wood’s on his right. He received one of Maj General George Thomas’s staff officers around 10 AM asking for additional assistance. Brannan knew that if his entire division were withdrawn from the line, it would expose the flanks of the neighboring divisions, so he sought his neighbor, Reynolds’s, assent. Reynolds agreed to the proposed movement, but sent word to Rosecrans warning him of the potential danger of that movement. However, Brannan remained in his position on the line, apparently waiting for Thomas’s request to be approved by Rosecrans. But Thomas’ staff officer believed that Brannan was in motion.


Brig. Gen. Thomas J. Wood chose to obey a questionable order from Rosecrans to reposition his division. In doing so, he opened up a crucial gap in the Union lines.

When Rosecrans received the message, he too was under the assumption that Brannan had left the line, and wanted Wood to fill the hole that would be created. His chief of staff, James A. Garfield, the future president, was engaged writing other orders so Rosecrans’s order was instead written by Frank Bond, his senior aide-de-camp. Bond wrote the following order: “The general commanding directs that you close up on Reynolds as fast as possible, and support him.” This order was sent to Wood directly, bypassing his corps commander. However, Wood’s movement actually opened up a real, very large gap in the line. 

When General Wood received this order at 10:50 AM, he was confused.

Since Brannan was still situated on his left flank, Wood was unable to “close up on” Reynolds (because Brannan’s division was in between). The only way to follow the language of the order was to withdraw from the line, march around behind Brannan and form up behind Reynolds, which would leave division-sized opening in the line. Wood spoke with corps commander McCook, and claimed later, along with members of both his and McCook’s staff, that McCook agreed to this plan.

General Longstreet’s Attack through the Gap on the Union right flank.

The Controversy

The modern version is that Woods knew there wasn’t a gap but moved anyway because he’d been reprimanded twice for disobeying orders that he thought were wrong. Wood questioned the order to move, but McCook reminded him to follow orders — Rosecrans had chewed out Wood twice before in this campaign for not immediately following an order. So Wood moved. 

Exactly what happened next is controversial. Henry Cist reported years later that Wood moved despite knowing that the order was an error. Cozzens standard text repeats this story, in which Wood waved the order, knowing it was an error, vowing to revenge his humiliation from Rosecrans. Cist was a Rosecrans partisan, and was defending him of all charges.  Both Dave Powell and Glenn Robertson in their works on Chickamauga refute Cist’s story.  Another source of the story comes from an unreliable source, Those Fateful Generals by E.V. Westrate, which gives words to the story, but offers zero evidence.  


Horseshoe Ridge, Chickamauga and Chattanooga National Military Park, 2008

It should be noted that Wood was never reprimanded or demoted, which seems inconsistent with an alleged action of such severe consequence that was intentional. 

By coincidence, Lt. Gen. James Longstreet had planned to lead a massive assault in that very area through a heavily forested area. At this moment, Longstreet had set up his part of the Confederate line into a tightly packed bowling ball that attacks right at the section of open line. The Confederates took advantage of the gap to full effect, shattering Rosecrans’s right flank. The resulting attack split the Union line in two. Rosecrans and his troops were routed and forced to retreat. Rosecrans attempted to rally retreating units, but decided to proceed to Chattanooga in order to organize his returning men and the city defenses. Moreover, Rosecrans began to build defensive positions for the expected confederate attack. 

General Thomas’s Defense of Horseshoe Ridge

The Rock of Chickamauga

The Union army escaped complete disaster thanks to the defense organized by Maj. Gen. George H. Thomas, who commanded the remaining forces on Horseshoe Ridge,  also called Snodgrass Hill, heroism that earned him the nickname “Rock of Chickamauga.” The army withdrew that night to fortified positions in Chattanooga. Thomas finally managed to retreat at the end of the day. 

Rosecrans sent Garfield to Maj. Gen. George H. Thomas whose XIV Corps were making a stand on Snodgrass Hill, with orders to take command of the forces remaining at Chickamauga and withdraw. But Garfield thought part of the army had held and, with Rosecrans’s approval, headed across Missionary Ridge to survey the scene. Garfield’s hunch was correct. His ride became legendary, while Rosecrans’s retreat reignited criticism about his leadership. 

Sheridan gathered as many men as he could and withdrew toward Chattanooga, rallying troops along the way. Learning of Thomas’s stand, Sheridan ordered his division back to the fighting, but they took a circuitous route and did not participate in the fighting. 


The Confederate army secured a decisive victory at Chickamauga but lost 20 percent of its force in battle. After two days of fighting, the Rebels forced the Union into a siege at Chattanooga.

Bragg’s leadership deteriorated into outright mutiny among his subordinate officers.

Sheridan’s return to the battlefield ensured that he did not suffer the fate of Rosecrans, who rode off to Chattanooga, leaving the army to its fate, and was soon relieved of command. Within a year, Garfield had been elected to the House of Representatives, accounted a hero for his courageous ride into danger, while Rosecrans had resigned the army, mainly as a consequence of his decisions. Ulysses Grant would take command at the Battle of Chattanooga.

Civil War Historian Dr. Lloyd W Klein

Civil War Historian Dr. Lloyd W Klein Dr. Lloyd W. Klein is Clinical Professor of Medicine in the Cardiology Division of the University of California, San Francisco. In addition, Dr. Klein is an accomplished consultant, author, lecturer and investigator. In addition, with over thirty-five years’ experience and expertise in managing myocardial infarction and tailoring coronary revascularization strategies. 

Moreover, Dr. Klein is a nationally recognized expert in individualizing coronary revascularization strategies. He has published extensively on analyzing operator quality and decision making.

Dr. Klein is also an amateur historian who has read extensively on the Civil War with a particular interest in political and military leadership and their economic ramifications. Furthermore, Dr. Klein has published numerous articles on the Civil War. Moreover, with a special concentration in why decisions were made and the people who made them. Lastly, using his professional experience in appraising leadership, he is especially insightful in evaluating the internal and external motivations which influenced decisions in battle and in the political hall.

Please see Dr. Klein’s Works:

Siege of Vicksburg

The Battle of Shiloh

The Hampton Roads Conference

Sherman’s March To The Sea

Why Did the North Win the Civil War (and, Alternatively, Why Did the South Lose?)

The Atlanta Campaign : The Conundrum of General Joseph E Johnston

The “Lost Order” Of General Lee

What caused the South to start the Civil War?

Was the Reconstruction of the Civil War successful?

Nathan Bedford Forrest’s Greatest Victory


  • https://www.battlefields.org/learn/civil-war/battles/chickamauga
  • https://apps.dtic.mil/dtic/tr/fulltext/u2/a437039.pdf 
  • Cozzens, Peter. This Terrible Sound: The Battle of Chickamauga. Urbana: University of Illinois Press, 1992
  • Robertson, William Glenn. “The Chickamauga Campaign: The Fall of Chattanooga.” Blue & Gray Magazine, Fall 2006.
  • Robertson, William Glenn. “The Chickamauga Campaign: McLemore’s Cove.” Blue & Gray Magazine, Spring 2007.
  • Robertson, William Glenn. “The Chickamauga Campaign: The Armies Collide.” Blue & Gray Magazine, Fall 2007.
  • Robertson, William Glenn. “The Chickamauga Campaign: The Battle of Chickamauga, Day 1.” Blue & Gray Magazine, Spring 2008.
  • Robertson, William Glenn. “The Chickamauga Campaign: The Battle of Chickamauga, Day 2.” Blue & Gray Magazine, Summer 2008.
  • Powell, David A. The Chickamauga Campaign: A Mad Irregular Battle: From the Crossing of Tennessee River Through the Second Day, August 22 – September 19, 1863. El Dorado Hills, CA: Savas Beatie, 2014. 
  • Powell, David A. The Chickamauga Campaign: Glory or the Grave: The Breakthrough, the Union Collapse, and the Defense of Horseshoe Ridge, September 20, 1863. El Dorado Hills, CA: Savas Beatie, 2015.

Was Chickamauga the bloodiest battle? The Gap in The Union Line at Chickamauga