Exactly 8:15 a.m. Local Time on August 6, 1945 -- conclusion of World War II (Pacific Theater, Japan)

from Writer's Almanac dot-org (American Public Media, Garrison Keillor):
Seventy years ago today, in 1945, the United States dropped an atomic bomb on the Japanese city of Hiroshima. The American B-29 bomber Enola Gay released the bomb, which was nicknamed “Little Boy,” at 8:16 in the morning, local time. Sixty-two thousand buildings were destroyed by the blast, which was equivalent to more than 12,000 tons of TNT. Eighty thousand people were killed on impact, and 35,000 died over the next week of their injuries or radiation poisoning. Sixty thousand more died over the next year. The bomb exploded over a hospital, and 90 percent of the city’s doctors were killed in the blast. It was the beginning of the end of World War II; Germany had already surrendered and Japan would follow after the U.S. dropped a second bomb on Nagasaki three days later.
A year later, The New Yorker devoted an entire issue to the publication of an article by John Hersey. The article, called simply “Hiroshima,” followed the lives of six survivors of the blast. The magazine’s founder and editor Harold Ross wrote to E.B. White: “Hersey has written thirty thousand words on the bombing of Hiroshima [...] one hell of a story, and we are wondering what to do about it [...] [William Shawn, managing editor] wants to wake people up, and says we are the people with a chance to do it, and probably the only people that will do it, if it is done.”
“Hiroshima” begins: “At exactly fifteen minutes past eight in the morning, on August 6th, 1945, Japanese time, at the moment when the atomic bomb flashed above Hiroshima, Miss Toshiko Sasaki, a clerk in the personnel department at the East Asia Tin Works, had just sat down at her place in the plant office and was turning her head to speak to the girl at the next desk.”