The 27th was part of Joe Johnston army that was gathered East of the Big Black River to relieve Vicksburg. On July 4th, the very day that Vicksburg surrender Grant sent Sherman's troops east across the Big Black to attack Johnston smaller army. Johnston retreated to Jackson Miss. This is the retreat where RW was captured.
"The Darkest Days of the War' by Peter Cozzens includes a description of the actions of the 27th at the Battle of Iuka in the Fall of 1862. Also the latest issue of "Blue & Gray" magazine deals with the Holly Springs Raid, which the 27th took part in as part of Griffith's Texas Brigade.