70 years after the bombing of Hiroshima and Nagasaki

The Executive Secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), Lassina Zerbo, concluded a six-day visit to Japan to participate in the ceremonies marking the 70th anniversaries of the bombing of Hiroshima and Nagasaki, on 6 and 9 August 1945 respectively. In Hiroshima, he met with Keiko Ogura, a survivor of the bombing of Hiroshima, and listened to her testimony of the events. Zerbo said: "I am here in Japan because of Hiroshima. To pay tribute to those who suffered, to help tell their story, and I commend Japan for its leadership."

In Nagasaki, Zerbo met Hibakusha Makoto Takahara, aged 87

The 70th anniversary of the bombings of Hiroshima and Nagasaki is an important occasion not only to remember those who suffered and continue to suffer and to recall the dangers of nuclear weapons, but also to renew the call for a total ban on nuclear testing.

In his message to the ceremony, delivered by Kim Won-Soo, Acting High Representative for Disarmament Affairs, UN Secretary Ban Ki-moon said “I pay tribute to the bravery of the Hibakusha and renew my resolve to advance our common cause of achieving a safer and more peaceful world, free of the nuclear shadow.”

On 7 August, Zerbo met Japan's Foreign Minister Fumio Kishida and gave a keynote speech at a symposium on nuclear disarmament issues at the Center for the Promotion of Disarmament and Non-Proliferation (CPDNP) in Tokyo. At the symposium, Zerbo said: "The Iran Deal is an excellent example of a successful multilateral approach. It could serve as a model for moving forward on the entry into force of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). On the CTBT's verification system, we have done our part. Our monitoring system is already far more effective than was originally envisioned. What we need now is political leadership."

Zerbo and Japanese Foreign Minister Fumio Kishida (left)

I thank you dearly for Japan's role and support. We find a source of motivation in your personal leadership.

From 24 to 25 August, the CTBT’s Group of Eminent Persons (GEM) will meet Minister Kishida and Executive Secretary Zerbo to discuss ways to advance the CTBT's entry into force. In his speech at the Hiroshima Peace Ceremony on 6 August, Japanese Prime Minister Shinzo Abe made reference to the upcoming GEM meeting.
Zerbo said: "The upcoming GEM meeting comes at an important time, 70 years since Hiroshima and Nagasaki and on the threshold of the CTBT's 20th anniversary. Following the recent deal with Iran, this is a golden opportunity to move forward and take this vital step towards non-proliferation and disarmament."
The CTBT's early entry into force is a crucial step on the road towards a world free of nuclear weapons

To commemorate the victims of the atomic bombs of Hiroshima and Nagasaki in Vienna, a GENBAKU NO-HI ceremony took place in the Rotunda of the Vienna International Centre on 6 August 2015. For the CTBTO, Jean Du Preez, head of the External Relations Section, delivered a statement .

GENBAKU NO-HI ceremony at the Vienna International Centre

The bombing of Hiroshima and Nagasaki are a reminder of what horrors nuclear weapons can inflict.


On 16 July 1945, U.S. scientists working on the Manhattan Project successfully detonated the first-ever nuclear explosion in the ‘Trinity’ test at Alamogordo, New Mexico. With World War II still dragging on in the Pacific, preparations moved forward to use nuclear bombs against Japan.

The test site after detonation: a crater of fused soil, also known as “Trinite” radiates from ground zero.

On 6 August 1945, at 08:15, the first bomb was dropped on the centre of Hiroshima. ‘Little Boy’ was a gun-type fission bomb, using a conventional explosive charge to fire one sub-critical mass of uranium into another. This kind of device had never been tested before, but the scientists were confident it would work.
And it did. The bomb had an explosive yield of around 13 kilotons. At the moment of detonation, a fireball was generated that raised temperatures to 4,000 degrees Celsius, turning Hiroshima – where many buildings were made of wood and paper - into an inferno. The blast created shock waves faster than the speed of sound. This and the radiation immediately killed everything within one kilometre of the hypocentre.

Pilot Paul Tibbets (centre) had named the aircraft after his mother.

After the blast, those who approached ground zero searching for the missing were exposed to radiation. Black rain, containing large amounts of radioactive fallout, caused widespread contamination. Estimates of casualties vary greatly. A more conservative estimate by the atomic archive lists 66,000 people killed immediately and a total death toll of 135,000, while the U.S.-Japanese Radiation Effects Research Foundation indicates a range of 90,000 to 166,000 deaths within the first four months.

Three days later, on the morning of 9 August, a second U.S. aircraft rose from the airbase at Tinian Island in the Pacific Ocean. The nuclear bomb it carried was code-named ‘Fat Man’. It was a more sophisticated plutonium-based implosion-type bomb which had been tested in the Trinity test. The primary target had been the city of Kokura. However due to a thick layer of clouds, the airplane’s crew reverted to the secondary target - Nagasaki.

'Fat Man' yielded 21 kilotons.

The bomb detonated at an altitude of approximately 500 metres and had a yield of 21 kilotons. Casualty estimates by the Radiation Effects Research Foundation for immediate deaths range from 60,000 to 80,000.
In the weeks that followed the bombings and Japan’s surrender, Hiroshima and Nagasaki became the object of intense studies by U.S. scientists. The Atomic Bomb Casualty Commission was founded to study the effects of radioactive contamination on the victims. Its results, including the extensive film and photo material taken at the time, remained classified for decades.

Nagasaki before and after

The bombings were officially justified as a necessary evil to end the war and avoid an invasion of Japan, which proponents claimed would have led to a greater loss of life. Critics inside and outside of the United States, however, questioned the morality and necessity of the bombings, arguing that the main reason for Japan’s surrender was the Soviet Union entering the war on the side of the allies and that the diplomatic means were not exhausted. Also the possibility of bombing an unpopulated area as a demonstration has been pointed out.

Boy carrying his injured brother a day after the Nagasaki bombing.

With nuclear testing, countries can develop even more powerful nuclear weapons. The CTBT bans all nuclear testing. At the CTBTO, we stand ready to implement this Treaty.

Over 2,000 nuclear tests were carried out after 1945 by different countries. They aided the proliferation of nuclear weapons and helped to develop weapons orders of magnitude more destructive than the Hiroshima and Nagasaki bombs.

Following decades of public campaigning and arduous multilateral negotiations, the Comprehensive Nuclear-Test-Ban Treaty (CTBT) was opened for signature in 1996. It bans all nuclear explosions. The Treaty has yet to enter into force.

The 1951 U.S. 'George' Test was already over 10 times more powerful than the Hiroshima and Nagasaki bombs.