 While at Georgia Tech, he took a job as a graduate teaching assistant.In 1973, McGarrah received his naval commission, and served in the United States Navy and the United States Navy Reserve for a total of 33 years.From 1973 to 1976, he served on the USS "Belknap" (CG-26) as Electronic Warfare Officer and Damage Control Assistant, and on the USS "Hoist" (ARS-40) after the "Belknap"s collision with the "John F. Kennedy" in 1975.