In the meantime, he served on the court-martial of Fitz John Porter for his tardiness at the Second Battle of Bull Run. He was convinced of Porter's guilt and voted with his fellow generals to convict Porter. The trial lasted almost two months, from November 1862 to January 1863, and, by its end, Garfield had procured an assignment as chief of staff to Major General William S. Rosecrans. Chief of staff for Rosecrans Generals' chiefs of staff were usually more junior officers, but Garfield's influence with Rosecrans was greater than usual, with duties extending beyond communication of orders to actual management of his Army of the Cumberland. Rosecrans had a voracious appetite for conversation, especially when unable to sleep; in Garfield, he found "the first well read person in the Army" and the ideal candidate for discussions that ran deep into the night. They discussed everything, especially religion, and the two became close despite Garfield's being 12 years his junior. Rosecrans, who had converted from Methodism to Roman Catholicism, softened Garfield's view of his faith. Garfield recommended that Rosecrans replace wing commanders Alexander McCook and Thomas Crittenden, as he believed they were ineffective, but Rosecrans ignored the suggestion. With Rosecrans, Garfield devised the Tullahoma Campaign to pursue and trap Confederate General Braxton Bragg in Tullahoma. After initial Union success, Bragg retreated toward Chattanooga, where Rosecrans stalled and requested more troops and supplies. Garfield argued for an immediate advance, in line with demands from Halleck and Lincoln. After a council of war and lengthy deliberations, Rosecrans agreed to attack. At the ensuing Battle of Chickamauga on September 19 and 20, 1863, confusion among the wing commanders over Rosecrans's orders created a gap in the lines, resulting in a rout of the right flank. Rosecrans concluded that the battle was lost and fell back on Chattanooga to establish a defensive line. Garfield, however, 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. Consequently, his ride became legendary and Rosecrans's error reignited criticism about the latter's leadership. While Rosecrans's army had avoided disaster, they were stranded in Chattanooga, surrounded by Bragg's army. Garfield sent a telegram to Secretary of War Edwin M. Stanton alerting Washington to the need for reinforcements to avoid annihilation. Lincoln and Halleck responded to the request for reinforcements by sending 20,000 troops to Garfield by