During the Maryland Campaign of September 1862, the 79th saw action at the battles of South Mountain and Antietam. During the latter battle, the Highlanders fought near Burnside's Bridge and were deployed as skirmishers leading an advance along the Sharpsburg Road near the Sherrick House. Despite heavy Confederate fire, they pressed on, managing to drive in part of Jones' Division and capturing a battery of artillery. However, the arrival of A. P. Hill's troops drove the 79th back into the suburbs of Sharpsburg, where they engaged in a vicious firefight around the Sherrick House. In spite of heavy fighting, the regiment escaped relatively lightly with only 40 men killed, missing or wounded.