From 1970 to 1972, Mackmull was assigned to the office of the army's Assistant Chief of Staff for Force Development as head of the Organization and Unit Training Directorate's Unit Authorizations Division. In this role, he oversaw the army's efforts to improve automated systems that accounted for unit personnel, equipment, vehicles and weapons. From June 1972 to March 1973, Mackmull served in Vietnam for the third time, this time as commander of the
1st Aviation Brigade. As U.S. forces were withdrawing, Mackmull managed the drawdown of aviation units and equipment — 15,000 soldiers and over 1,000 aircraft — with no pause in combat aviation operations. He was promoted to
brigadier general in February 1973. In May 1973, Mackmull was assigned as deputy commander of the Army Aviation Systems Command at
Granite City Army Depot in
St Louis, Missouri. During this posting, he had responsibility for centralizing and automating the army's aviation logistics systems. In May 1974, Mackmull was assigned as assistant division commander (ADC) of the
101st Airborne Division, and he served until May 1976. As ADC, he oversaw design and implementation of the army's Combat Aviation Management System, multiple field manuals on air assault operations, and aviation battle drills. From May 1976 to June 1977, Mackmull was chief of staff for the
XVIII Airborne Corps. In June 1977, Mackmull was assigned as commander of the
John F. Kennedy Special Warfare Center and School, and he was promoted to
major general in July. As head of
Special Forces, Mackmull led post-Vietnam War modernization of equipment, doctrine, tactics, and command relationships. and oversaw organization of
Delta Force and Special Operations aviation doctrine and tactics. Mackmull commanded the 101st Airborne Division from June to 1980 to August 1981, and his accomplishments in this position included organizing Task Force 160, now the
160th Special Operations Aviation Regiment (Airborne). The 160th Aviation Regiment supports Special Operations by helicopter attack, assault, and reconnaissance, frequently on short notice, at night, and at high speed and low altitude. In August 1981, Mackmull was assigned as commander of the XVIII Airborne Corps, and he was promoted to
lieutenant general in September. In 1982, he participated in the Army Aviation Review study project as chairman of the Tactical Employment Committee. The committee's report and recommendations led to recognition of a future requirement for a helicopter that could engage in air-to-air combat and the 1983 establishment of the
Army Aviation Branch. In addition, Mackmull oversaw the training for, planning, and execution of the army's participation in the
United States invasion of Grenada. Mackmull retired in June 1984. ==Retirement and death==