Wilkerson arrived as an Army officer piloting an OH-6A Cayuse observation helicopter and logged about 1100 combat hours over a year. He flew low and slow through South Vietnam, and was involved in one incident in which he says he prevented a war crime by purposely placing his helicopter between a position that was full of civilians, and another helicopter that wanted to launch an attack on the position. He also had many vocal disagreements with his superiors and his own gunner crew over free-fire zones, including an incident in which one of his crew shot a wagon that wound up having a little girl inside it. He went on to Airborne School and Ranger School before receiving his Bachelor of Arts degree in English literature and graduate degrees in international relations and national security. He attended the Naval War College in Newport, Rhode Island, and later returned there to teach. He later served as deputy director of the Marine Corps War College at Quantico.