 The position of Chief of Staff for a general was usually held by a more junior officer , but Garfield 's influence with Rosecrans was greater than usual , with duties extending beyond mere communication of orders to duties that involved actual management of his Army of the Cumberland . Rosecrans had a voracious appetite for conversation , especially when he was 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 . The two became close in spite of Garfield 's being twelve years junior to Rosecrans , and their talks covered all topics , especially religion ; Rosecrans , who had converted from Methodism to Roman Catholicism , succeeded in softening Garfield 's view of his faith . Garfield recommended that Rosecrans replace wing commanders Alexander McCook and Thomas Crittenden , whom he believed ineffective , but Rosecrans ignored the suggestions . 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 . 
