Ordered to the Republic of Vietnam in July 1965, General Trainor was assigned as an advisor to a Vietnamese special operations group. After a year in Vietnam, he was promoted to lieutenant colonel and returned to Quantico, where he served for three years as an instructor at the Command and Staff College. In 1969, Trainor attended the Air War College, Maxwell Air Force Base, Alabama. During his War College course he was awarded the Anderson Memorial Award for the "best paper dealing with politico-military thought" and designated a "Distinguished Graduate" upon completion of the course in June 1970. He then served another tour in the Republic of Vietnam, where he commanded the 1st Battalion 5th Marines, and later the 1st Reconnaissance Battalion of the 1st Marine Division. Following his return to the United States in 1971, Trainor was assigned to Headquarters Marine Corps, where he served as a plans officer. During this tour, he was promoted to colonel on January 3, 1972. From July 1974 through June 1975, he served as Deputy Director of the 1st Marine Corps District, headquartered in New York. On July 1, 1975, he assumed duties as Director and held this post until his advancement to brigadier general in April 1976. At this time, he assumed duties as assistant depot commander, Marine Corps Recruit Depot Parris Island, South Carolina. On April 14, 1978, he assumed the duties of deputy for education/director, education center, Marine Corps Development and Education Command, Quantico. During this tour of duty, he was promoted to major general. He was subsequently transferred to Headquarters Marine Corps in April 1981 and assigned duty as director, Plans Division, Plans, Policies and Operations Department. Upon promotion to lieutenant general on June 15, 1983, he was assigned duty as the deputy chief of staff for plans, policies and operations, Headquarters Marine Corps. He served in this capacity until his retirement on July 1, 1985. General Trainor worked for "The New York Times" as chief military correspondent from 1986 to 1990, covering events in Central America and Africa. He then joined Harvard University's John F. Kennedy School of Government as Director of the National Security Program from 1990 to 1996. Later, he was a Senior Fellow for National Security for the Council on Foreign Relations. During that time, Trainor appeared frequently on national news media as an expert on military and foreign affairs. He covered the invasion of Iraq for NBC and MSNBC. He and Michael R. Gordon have written three books together: "The Generals' War", which covers the 1991 Gulf War, "Cobra II", which covers the Iraq War begun in 2003 and concludes with "".