Lieutenant General Merryman's Army Aviation career spanned from Second Lieutenant, flying the border ASA fixed-wing pilot in Germany to Lieutenant General, Deputy Chief of Staff of the Army for Research, Development, and Acquisition. Between these two mileposts he also was a great combat commander in Vietnam, the Director of Army Aviation, and the Commanding General of the U.S. Army Aviation Center.

In 1961, he was assigned as the first Aviation Officer at the Field Artillery School where he gained approval for establishing an Aerial Field Artillery Battery. He served on the "Howze Board" in 1962, developing methods to evaluate the capabilities of various aerial firepower systems. From 1964 to 1966 he was with the FAA. In 1967, he went to Vietnam, where he was S-4, 12th Combat Aviation group for two months, followed by command of the 269th Combat Aviation Battalion. His innovations in command and control, the use of gunships, and aerial medical evacuation techniques were well known.

He returned to Washington after a highly successful tour and was assigned to ACSFOR and DCSOPS, Operations Directorate until 1971 when he returned to Vietnam to command the 17th Combat Aviation Group. He then served as Executive to the Assistant Secretary of the Army for R&D. In this assignment, he advised the Army Secretariat on all matters pertaining to aviation programs and was intimately involved in developing and securing approval of aviation programs such as the AH-64 APACHE.

In August 1973, he became Director of Army Aviation. In January 1977 while assigned to DCSPER TRADOC, he managed and emphasized the improvement of career patterns of Aviation Warrant Officers. He was then elevated to Deputy Chief of Staff for Combat Developments at TRADOC. From December 1978 to July 1980, as CG of the U.S. Army Aviation Center, he established Fort Rucker as the focal point for Army Aviation organization, doctrine, and material requirements.

From July 1980 to August 1984, General Merryman served as Assistant Deputy Chief of Staff and Deputy Chief of Staff for Research, Development and Acquisition. In these positions, he contributed to the successful development and acceptance of Army Aviation materiel. The greatest achievement of his career was changing the organizational structure of Army Aviation where through his personal efforts an Aviation Brigade was approved for all Divisions in the Army.