During the Vietnam War, Garrison participated in the notorious Phoenix Program. According to Mark Bowden, " had served two tours in Vietnam, part of it helping to run the infamously brutal Phoenix Program, which ferreted out and killed Viet Cong village leaders." From 1981 to 1983, Garrison commanded the 1st Battalion, 505th Infantry, 82d Airborne Division, at Ft Bragg NC. In 1982 he led an 808 man task force, TF 1/505, on the first six month Sinai mission as part of the Multinational Force and Observers, serving as a buffer between Israel and Egypt, and was present when Israel handed over the Sinai to Egypt. Garrison spent most of his career in special operations units, including the U.S. Army's Intelligence Support Activity as the commander of its operations squadron and the 1st Special Forces Operational Detachment-Delta from 1985 to 1989. His last command was the John F. Kennedy Special Warfare Center. He is known for being the commander in charge of Task Force Ranger during Operation Gothic Serpent in Somalia. Garrison took full responsibility for the tactical setbacks experienced in Operation Gothic Serpent, which effectively ended his military career. Mark Bowden, the author of Black Hawk Down: A Story of Modern War, described Garrison as a military ascetic. According to Bowden's description Garrison tirelessly worked to serve his country and would do anything for his soldiers. Some of Garrison's subordinates have also spoken publicly about their former commander. Staff Sergeant Dan Schilling, an Air Force Combat Controller who took part in Operation Gothic Serpent, shared his feelings about Garrison in the book The Battle of Mogadishu: Firsthand Accounts From The Men of Task Force Ranger. On page 187 of the text Schilling stated "I should pause here for a moment to say a few words about General Garrison. Many know his record and command history. I'm not the person to expound on his exploits; in fact I don't knowthe man very well. But I will say he is the finest general officer I have ever worked for and probably ever will. He understood his men and how we thought, what we wanted and needed, and understood the situation anywhere he was, immediately and completely. He is the finest leader an operator could ask for. It wasn't a shame that his career was derailed after our deployment; it was a criminal act committed by political cowards." By September 1996, Garrison had retired at the rank of major general and settled into a ranch near the community of Hico, Texas.
