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| Damage Surveys Immediately after the Bombing
First surveys: looking through the confusion to confirm an "atomic bomb"
Immediately after the atomic bombing, the Kure Naval Base, the Army Marine Training Division and other military units stationed near Hiroshima sent relief teams to the city and immediately began investigating the disaster. These investigations were for the purpose of measuring the destructive power of the new type of weapon and recommend countermeasures.
Sixteen hours after the bomb exploded, the US announced to the world that it had dropped an atomic bomb. The Japanese government and military leaders learned from this "Truman statement" that the bomb had been "atomic." The government and Imperial Headquarters hurriedly dispatched to Hiroshima a survey team made up primarily of scientists who had been involved in Japan's A-bomb research. Their task was to confirm Truman's statement. One after the next, other army and navy units sent teams made up mainly of doctors and university researchers.
The Imperial Headquarters Survey Team held a joint army-navy meeting on August 10, and this body confirmed that Hiroshima had been destroyed by an atomic bomb. They immediately sent a telegraph to headquarters and prepared a written report.
In response, the government and the military issued statements to the international community criticizing the US for using such a bomb, but at home, they sought to hide the fact that an atomic bomb had been used. They sought to continue the war. However, the fact that atomic bombs had been dropped led to a decision in the Imperial Council in the morning of August 10 to accept the Potsdam Declaration. This decision took the form of an official document issued by the emperor ending the war on the 15th. However, it was not until August 14, the day before the end of the war, that the Japanese government told its own people about the atomic bomb. Meanwhile, most of the survey teams in Hiroshima continued their investigations even after it was clear that the bomb was atomic.
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Survey activities by the Kure Naval Base
"Naval Base" in the Japanese imperial navy were assigned to manage police and affiliated organizations in a given naval district. The Kure Naval Base controlled the Kure Naval Arsenal, where the Battleship Yamato and other famous ships were built. It also employed many engineering officers.
Immediately after the bombing, the Kure Naval Base sent a time in for rescue and relief, but also organized a survey team that went in on the day of the bombing and stayed to investigate the situation until the next day. They returned on the 7th to write a sophisticated scientific report.
The survey team from the Kure Naval Base took part in a joint investigation on the 8th with the team from the Imperial Headquarters Navy Team. A conference was held that evening. This report displayed a profound understanding of the heat ray burns and other aspects of the A-bomb. Having already heard about the Truman statement, this group stopped just short of a positive conclusion that Hiroshima had been destroyed by an atomic bomb. Their estimates of hypocenter location and altitude were quite accurate, even compared to subsequent studies.
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Opinion paper regarding the new type of bomb written by the commander, Experimental Dept. of the Electrical Weapons of the Kure Naval Arsenal
August 7, 1945
Collection of Kure City Planning Department Maritime Museum Promotion Office
Report regarding Hiroshima air raid damage by Kure Naval Base
August 8, 1945
Collection of Kure City Planning Department Maritime Museum Promotion Office
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Survey activities by the Army Marine Training Division
The Marine Training Division retrained soldiers originally trained for land shipping tasks. The main training task at that time was the training of suicide bombers expected attack ships with small boats filled with explosives during the decisive battle for the mainland. This facility, previously a thread factory was in Ujina-machi (Ujina-higashi 5-chome, Minami-ku) about 4 km from the hypocenter. Because it was only slightly damaged, crowds of survivors arrived there after the bombing, and the building became a hospital. Later, it served as the base for various survey teams.
History is based on listening. Interviews may be only a first step in an investigation, but they offer quick information of enormous value. This material states that the destructive power of the bomb was enormous, but with sufficient preparation and safety measures, it is nothing to be afraid of.
Statement by the US that it had dropped an atomic bomb
Sixteen hours after the dropping of the atomic bomb, the US president himself announced to the world that an atomic bomb was dropped in Hiroshima. He called on Japan to accept the Potsdam Declaration. In Japan, this statement was immediately translated and conveyed to government and military leaders.
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Army Marine Shipping Training Division, material regarding the Hiroshima Bombing
August 8, 1945
Collection of Hiroshima Peace Memorial Museum
Donated by Seiichi Niizuma
Enemy information (Truman Statement)
August 7, 1945
Collection of Nishina Memorial Foundation
The Domei News Agency translated and distributed the Truman Statement.
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Imperial Headquarters Survey Team -Confirming the atomic bomb
After learning of the Truman statement, Imperial Headquarters dispatched a team to Hiroshima to confirm that the bomb was atomic.
That team, led by Lieutenant General Seizo Arisue of the Joint Staff, included Yoshio Nishina from the Institute of Physical and Chemical Research and seven other officers who had been involved in the Ni Project (A-bomb research).
They arrived by military plane at the Yoshijima Air Field on August 8. They surveyed military facilities in the city and received reports from the organizations that had arrived ahead of them.
Based on this information, they held a joint army-navy meeting on the 10th and came to the conclusion that Hiroshima had been destroyed by an atomic bomb.
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Fourth Report of the War Department Hiroshima Damage Survey Team（telegram）
August 9, 1945
Collection of Hiroshima University Research Institute for Radiation Biology and Medicine
Initial draft of a report on the special bomb
Collection of Hiroshima Peace Memorial Museum Donated by Seiichi Niizuma
Based on the findings of various military organizations, those present at this meeting concluded that Hiroshima had been destroyed by an atomic bomb.
Sand and other specimens sent by Yoshio Nishina
Collection of Hiroshima Peace Memorial Museum
Donated by Shinji Okano
Journal written by Motoharu Kimura showing the levels of radiation found in the samples sent by Yoshio Nishina.
Collection of Hiroshima Peace Memorial Museum
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Survey activities by the War Department Hiroshima Damage Survey Team
The War Department Hiroshima Damage Survey Team＊ observed the air-raid damage to the city and the condition of patients in the hospitals on August 9. In the process, they discovered that X-ray film at the Red Cross Hospital had been exposed. From this, they recognized the need to investigate radiation. They sent a telegram requesting a radiation expert. This report, dated the 9th, describes the damage and relief activities in the city, focusing on the situation at army hospitals. However, it does mention the exposure of the X-ray films at the Red Cross Hospital and called for further study.
＊ The Army Medical School was the source of the War Department Hiroshima Damage Survey Team.
Joint meeting sponsored by Imperial Headquarters
The Hiroshima Army Ordnance Supply Depot stood southeast of Hijiyama Hill, where it was shielded from the bomb and escaped the fire. On August 10 at 10 a.m. a joint Army-Navy Meeting was held by Imperial Headquarters.
This conference heard reports from the Second Army, the Marine Headquarters, the Kure Naval Base and other organizations.
Based on the findings of various military organizations, those present at this meeting concluded that Hiroshima had been destroyed by an atomic bomb. Lieutenant Colonel Seiichi Niizuma of the Imperial Headquarters Survey Team prepared the draft report from the joint meeting. In his initial draft written clearly in pencil he clearly stated, "We conclude it was an atomic bomb."
This finding was quickly telegraphed to central headquarters.
The Imperial headquarters Survey Team ended its activities after this report, but other teams dispatched by military organizations remained in Hiroshima and continued their investigations.
Yoshio Nishina of the Institute of Physical and Chemical Research measuring radiation
On instructions from Yoshio Nishina of the Institute of Physical and Chemical Research, his team, who entered the city with the Imperial Headquarters Survey Team on August 9, took samples from 28 locations (specimens from 26 of those locations exist today). He sent them by air to the Institute of Physical and Chemical Research. After putting the sand in the bottles, he wrote the location from which the sample was taken.
By the evening of the 10th, Motoharu Kimura, a researcher at the Institute of Physical and Chemical Research, had measured the copper radiation from the samples sent by the Imperial Headquarters Survey Team with a Lauritsen electroscope. The readings showed that the copper in those samples had become radioactive after being hit by neutrons released by the nuclear fission of the atomic bomb. These measurements were definitive evidence that the bomb dropped on Hiroshima was atomic. The report goes on to say, "When measured again the next day, no measurable radiation was found because of the short half-life." It is believed that these were the first scientific measurements of A-bomb radiation.
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