Thomas would earn the undying loyalty of soldiers like Henry Van Ness Boynton, who won the Congressional Medal of Honor fighting under him in 1863. Boynton wrote that Thomas "looked upon the lives of his soldiers as a sacred trust, not to be carelessly imperiled. Whenever he moved to battle, it was certain that everything had been done that prudence, deliberation, thought and cool judgment could do under surrounding circumstances to ensure success commensurate with the cost of the lives of men. And so it came to pass that when the war ended it could be truthfully written of Thomas alone that he never lost a movement or a battle."
But for Thomas, every battlefield success seemed to stir controversy or the jealousy of ambitious rivals. Unlike other noted generals, he had no home-state politicians to lobby on his behalf in Washington. Ulysses S. Grant, for example, was championed by Illinois congressman Elihu Washburne, and Sherman by his brother, Ohio senator John Sherman. For Thomas, every step upward depended solely on his performance in the field.
In one of the war's first skirmishes, he led a brigade in the Shenandoah Valley that bested Confederates under Stonewall Jackson. When the dashing Rebel J.E.B. Stuart heard that Thomas was commanding Union cavalry, he wrote to his wife that "I would like to hang him as a traitor to his native state." Even after that, there was lingering doubt among some Unionists, including Lincoln. Unlike Grant, Sherman, George McClellan and some other ranking Union officers who had broken their military service with years as civilians, Thomas had been a soldier since the day he entered West Point. Yet when his name came up for promotion, the president, restrained by Northern radicals and surrounded in the Federal bureaucracy by Southerners, said, "let the Virginian wait." But Sherman among others vouched for Thomas, and soon the Virginian was elevated to brigadier general and ordered to organize troops away from Virginia, beyond the Appalachians.
There, in January 1862, he sent a bulletin of encouragement to a Union hungry for good news. After an 18-day march on muddy roads, his division confronted Rebels at Mill Springs, Kentucky. Amid cold rain and gun smoke, he led his outnumbered troops in repulsing Confederates under Maj. Gen. George Crittenden and then drove them across the Cumberland River. Though not a massive victory, it was the first notable Northern success of the war, turning back a Confederate move from eastern Tennessee into Kentucky. Thomas was promoted to major general, an advancement that would soon create friction with his old roommate "Cump" Sherman and Grant, who had become so close that an affront to either was resented by both.
After winning praise for capturing Forts Henry and Donelson in western Tennessee, Grant had fallen out of favor for mismanaging and very nearly losing the bloody Battle of Shiloh. He was criticized for taking 13,000 casualties and was suspected of drinking on the job. Sherman, whose excitability and wild overestimates of Rebel strength had caused some to question his sanity, had fought bravely after an initial mistake at Shiloh. When Union forces moved south toward Corinth, Mississippi, that spring, Union general Henry Halleck shunted Grant into a figurehead role and gave Thomas temporary command of the wing that included Grant's Army of the Tennessee. Grant, angered, was talked out of quitting by Sherman. Grant would not forget the incident.
Grant and Sherman would redeem themselves by grasping control of the Mississippi River in the costly, circuitous campaign that resulted in the capture of Vicksburg in mid-1863. While they were operating on the Mississippi, Thomas led a corps in Rosecrans' Army of the Cumberland, earning respect in fights like that at Stones River, where he declared, "This army does not retreat," and backed up his words with actions on the field. There and at Tullahoma, Rosecrans' force pressed the Confederates back into eastern Tennessee.
As Thomas rose, he proved to his men that his addiction to detail and his insistence on preparation saved lives and won battles. His generalship behind the front, before the battle, was generations ahead of his peers. He organized a professional headquarters that made other generals' staff work seem haphazard. His mess and hospital services, his maps and his scouting network were all models of efficiency; he was never surprised as Grant had been at Shiloh. He anticipated modern warfare with his emphasis on logistics, rapidly repairing his railroad supply lines and teaching his soldiers that a battle could turn on the broken linchpin of a cannon. He demanded by-the-book discipline, but taught it by example. He made no ringing pronouncements to the press. His troops came to understand his fatherly concern for their welfare, and when they met the enemy they had faith in his orders.
In late summer, Rosecrans moved against the Rebel stronghold of Chattanooga, a crucial gateway between the eastern and western theaters of war. Confederate general Bragg pulled out of the town onto the dominating nearby mountains, waiting for Maj. Gen. James Longstreet to bring reinforcements from Virginia. When they came, Bragg threw everything into an assault on Union lines along Chickamauga Creek, just inside Georgia. Thomas' corps was dug in on the Union left. On the second day of furious fighting, a misunderstood order opened a wide gap on his right. Longstreet's Rebels crashed through; with the always aggressive John Bell Hood's division leading, they bent the Union line into a horseshoe.
Rosecrans, certain the battle was lost, retreated into Chattanooga with five other generals and thousands of blue-uniformed soldiers. But Thomas inspired his men to stand fast, and only their determined resistance saved his army from destruction. They held all that afternoon against repeated Confederate assaults, withdrawing into Chattanooga after nightfall. It was the greatest of all battles in the West, and since that day, Thomas has been known to history as the Rock of Chickamauga.
For their actions, Rosecrans was fired and Thomas took command of the Army of the Cumberland. But the Union situation remained dire. Bragg, still holding those formidable mountains, laid siege to Chattanooga. Grant, commanding Union armies between the Mississippi and the mountains, ordered Thomas to hold the city "at all costs," and rushed troops east to help.