King was frequently detailed to clerk and quartermaster duties, culminating in his March 1863 promotion to quartermaster sergeant, a rank that nominally precluded involvement in combat. King, however, requested and was granted permission by his brigade commander to join in battle outside his line of duty at Missionary Ridge on November 25, 1863. There, King twice charged ahead of his unit against fortified Confederate positions, entering hand-to-hand combat on the first occasion, and penetrating a gap in Alexander P. Stewart's division on the ridge summit in the second case. King was among the first to crest the ridge, and the piercing of the Confederate battle line triggered Stewart’s retreat from the heights. King was wounded in the process, suffering a gunshot wound to his right arm that inflicted a lifelong disability and nearly necessitated amputation.