Chambersburg During the Gettysburg Campaign June 14-July 6, 1863 Chambersburg lay squarely in the middle of the valley up which Lee launched his second and last grand offensive in June 1863. The evacuation of local militia units left the town undefended, and it was rapidly occupied by the advancing Southern army. Chambersburg was used as a central staging area by the Confederates; its importance to their operations increased when the massive confrontation began to develop in Gettysburg, approximately twenty-five miles east across the South Mountain ridge. Following their defeat at Gettysburg, the Confederates withdrew from Chambersburg toward the Potomac River. Hot in pursuit was Samuel's regiment, and Samuel himself was among the first Union soldiers to reenter the town.