By April 25, 1951, he was a private first class serving with Company I of the 7th Infantry Regiment, 3rd Infantry Division. On that day, near Tongmang-ni, his company came under attack from a numerically superior Chinese force. From his defensive position, Gilliland had a clear view of the defile through which many of the attackers were approaching. Using his automatic rifle, he fired continuously into the defile, even after suffering a severe head wound while chasing down two Chinese soldiers who had breached the defensive line. When orders came to pull back, he voluntarily stayed behind and provided covering fire so that the rest of his unit could withdraw. He was never seen again.