As the U.S. Marine Corps helicopter lifted from the roof of the American Embassy in Saigon at daybreak on April 30, 1975, I thought about the carnage that would result from a heat-seeking missile fired by Vietnamese Communist forces gradually encircling the besieged capital of the dying Republic of Vietnam. Exhausted by a lack of sleep for the previous week, I no longer felt fear, only curiosity. Tears welled up in my eyes, perhaps due in part to the anguish of witnessing the tragic events unfolding before me, but also from caustic smoke belched out of rooftop incinerators glowing cherry-red...