Staff writers answer readers' question related to the atomic bomb

(1)Was the atomic bomb really dropped at 8:15am?

I heard that the atomic bomb wasn't dropped at 8:15am, as we learned in school. Is this true?

In the daily log of the former Hiroshima Meteorological Observatory, the time of 8:30 was changed to 8:15.

This question comes from a junior writer. To respond, let's first consider the issue involving the time the bomb was dropped and the time it actually exploded.

At the Peace Memorial Museum in Hiroshima, "8:15am" is stated for both the time the bomb was dropped above the city of Hiroshima and the time the bomb exploded.

The museum's famous pocket watch stopped at 8:15 and 40 seconds. The man who owned the watch was about 1.6 kilometers from the hypocenter. However, a total of 83 watches have been donated to the museum and they display differing times.

Of course, it's hard to trust the accuracy of watches in those days. And we can't really know whether or not the watches stopped immediately after the bomb exploded. We need some type of more dependable evidence. Perhaps the meteorological records of that time will be helpful?

The time was revised from 8:30

The local meteorological observatory in Hiroshima has a record of the change in air pressure noted at that time. This observation was made at the observatory's former site, about 3.7 kilometers from the hypocenter. The handwriting on the graph indicates "blast 8h 18m 6"-apparently, 8:18 and 6 seconds.

There is also a daily log with the note "B29 attacked Hiroshima around 8:15," but it looks like this note was revised and that, originally, a time of "8:30" was recorded. This makes the mystery even more difficult to resolve.

There are different records of the dropped time

Next, I looked into references made in Japan right after the atomic bomb was dropped. At 6:00pm on August 6th, the main radio station in Osaka stated that the bomb was dropped at 8:20. The next day, on August 7th, the Kure Arsenal also reported a time of 8:20. However, the Kure Naval Base first announced a time of 8:10, then later revised this time to 8:16.

Reference	Drop Time	Explosion Time
"Was the Atomic Bomb Really Dropped at 8:15?" by Kazuo Chujo	-	8:06
report concerning the bombing of Hiroshima by Kure Naval Base	-	approximately 8:10 (revised to 8:16 )
material concerning the bombing of Hiroshima by the Military Training Division	approximately 8:15	8:15
exhibit in the Hiroshima Peace Memorial Museum	8:15	8:15
"Ruin from the Air" by Gordon Thomas	8:15:17	exactly 8:16
"The Making of the Atomic Bomb" by Richard Rhodes	43 seconds before the explosion	8:16:02
"Now It Can Be Told: The Story of the Manhattan Project" by Leslie R. Groves and Richard H. Groves	9:15:30 (1 hour time difference)	50 seconds after the drop
the former Hiroshima Meteorological Observatory (record of atmospheric pressure)	-	8:18:06 (the blast)
the former Hiroshima Meteorological Observatory (daily log)	-	approximately 8:30 irevised to 8:15
radio broadcast on August 6th ("30 Years after the Atomic Bomb: the Post-War History of Hiroshima")	8:20	-
opinion paper regarding the new type of bomb by the Commander of the Experimental Weapons Department, Kure Arsenal	about 8:20	-

According to plan?

How about in the United States? According to a book written by the director of the Manhattan Project, Leslie R. Groves, the atomic bomb was dropped at 8:15 and 30 seconds; 50 seconds later, it exploded. A book by an American journalist who interviewed the crew of the Enola Gay indicates a drop-time of 8:15 and 17 seconds, with the bomb exploding exactly at 8:16. Compared to the original flight plan made on the island of Tinian, the difference is less than one minute from this recorded time.

But a former journalist, Kazuo Chujo, 80, doubts that the plane was able to arrive at its destination at the scheduled time. Even today, airplanes have difficulty arriving at their destinations on time. Mr. Chujo grew up in Hiroshima and experienced the atomic bomb when he was 19 years old. He wrote a book in 2001 entitled "Was the Atomic Bomb Really Dropped at 8:15?"

So my research reveals that there are differences in regard to the time the atomic bomb was dropped. Still, it's true that the time of "8:15" has become an accepted fact for the people of Hiroshima. The director of the International Peace Promotion Department at Hiroshima City Hall remarked, "Unless we uncover new evidence, we would never change the time of the silent prayer at the Peace Memorial Ceremony."(Kyoko Morioka, staff writer)

Kure Arsenal
The former Japanese Navy's largest arsenal of weapons. In 1903, the Kure naval arsenal and shipyard were merged and Kure Arsenal was established. In 1941, the "Yamato" battleship was constructed here.
Kure Naval Base
One of the former navy's three local bases. It was established by the Japanese government in 1886 to strengthen forces in this area.
Manhattan Project
An American project to produce atomic bombs during World War II, out of fear that Germany would develop an atomic bomb first. America successfully tested an atomic bomb in July 1945.
Tinian
An island 5 kilometers from Saipan. On August 6th, 1945, the Enola Gay flew from this island with the atomic bomb.