 Upon entering the Marine Corps, Leftwich completed The Basic School at Marine Corps Base Quantico in Virginia in January 1954, and later served as a rifle platoon commander with the 2nd Marine Division at Camp Lejeune in North Carolina.During 1955–56, he served with the 3rd Marine Division on Okinawa.On his return to the United States, he was stationed at Camp Pendleton in California, where he was promoted to captain in July 1957.