When I first arrived in Vietnam in 1962, common practice was to take a break during the hottest part of the day, usually from about 1:00 p.m. until 3:00 p.m. or so—simply because it was too hot to work. The Vietnamese often slept during those hours, so we Americans referred to the practice as a siesta. The Vietnamese called it giac ngu trua, that is, noon nap.
The Americans, almost all military assigned to the Military Assistance and Advisory Group (MAAG), followed the practice, partly because air conditioning was rare and hard to come by. In the field of combat, of course, no one napped.
When I returned to Vietnam after the 1973 pullout of U.S. troops, the Vietnamese civilian population still followed the siesta practice, but we Americans no longer did. On the one hand, we had air conditioning everywhere—in our offices and our quarters; on the other, and the tense circumstances no longer allowed that kind of leisure. As the situation deteriorated and the North Vietnamese drew close to Saigon, we did well just to get enough time to sleep at night. During the last weeks of April 1975, when we were surrounded and awaiting the final attack on the city, we stopped sleeping altogether.