The blast of strings of exploding firecrackers jerked me awake as Vietnamese neighbors continued their celebrations into the early hours of the morning. It was Saigon, January 31, 1968, the first day of the year of the traditional lunar calendar, Tet Nguyen Dan, and the most important Vietnamese festival. Amid the cacophony I noticed a loud, methodical rat-tat-tat that shook our apartment shutters as though someone was banging on them with a hammer. I’d heard that sound before in the battlefield, the roar of a heavy-caliber machine gun, and it seemed to be shooting up Pasteur Street just three room-lengths away. A weapon that lethal had not been discharged in Saigon since the overthrow of President Ngo Dinh Diem four years earlier.