In the momentous days in 1975 leading up to the fall of Saigon, Ralph White, then a 27-year-old banker for Chase Manhattan in its South Vietnam office, was tasked with keeping the bank’s staff safe. But within days after his arrival, it became clear his true responsibility would be to evacuate the staff and its families. White, the author of “Getting Out of Saigon,” his account on how he managed to evacuate 113 Vietnamese, will describe the events for members…