バレー方面作戦
Posey suffered a slight wound at the Battle of Cross Keys in June 1862 during Major General Stonewall Jackson's Valley Campaign. His regiment fought in the Seven Days Battles with the Army of Northern Virginia under General Robert E. Lee. He served as the temporary commander of the brigade of four Mississippi infantry regiments, commanded by Brigadier General Winfield S. Featherston, during the Northern Virginia Campaign and the Maryland Campaign. Posey's regiment fought at Fredericksburg in December 1862, successfully repelling a Union attack.