1945: Destruction of Hiroshima and Nagasaki by Atomic Bomb


I offer cordial greetings to the organizers and participants in the seventy-fifth solemn anniversary of the nuclear bombing of Hiroshima in 1945, and in a special way to the hibakusha survivors of the original tragedy.

I was privileged to be able to come in person to the cities of Hiroshima and Nagasaki during my Apostolic Visit in November last year, which allowed me to reflect at the Peace Memorial in Hiroshima and at Hypocenter Park in Nagasaki on the destruction of human life and property wrought in these two cities during those terrible days of war three quarters of a century ago.

Just as I came to Japan as a pilgrim of peace last year, so I continue to hold in my heart the longing of the peoples of our time, especially of young people, who thirst for peace and make sacrifices for peace. I carry too the cry of the poor, who are always among the first victims of violence and conflict.

It has never been clearer that, for peace to flourish, all people need to lay down the weapons of war, and especially the most powerful and destructive of weapons: nuclear arms that can cripple and destroy whole cities, whole countries. I repeat what I said in Hiroshima last year: “The use of atomic energy for purposes of war is immoral, just as the possessing of nuclear weapons is immoral” (Address at the Peace Memorial, 24 November 2019).

May the prophetic voices of the hibakusha survivors of Hiroshima and Nagasaki continue to serve as a warning to us and for coming generations! To them, and to all who work for reconciliation, we make the words of the psalmist our own: “For love of my brethren and friends, I say: Peace upon you!” (Ps 122:8).

Upon all who commemorate this solemn anniversary I willingly invoke abundant divine blessings.

From the Vatican, 15 July 2020

The world is not at war in the same way that it was in 1945, but Pope Francis has warned several times in the last few years that we are in the middle of a third world war fought piecemeal. In addition to this there are still dozens of internal and international armed conflicts going on in our world today.

Pope Paul VI who instituted the World Day of Peace on the first of January each year, did so in the hope that peace would lay the foundation for the year ahead. His theme for the World Day of Peace Message 1972 “If you want peace, work for justice” has become a cornerstone of Catholic Social Teaching.

When Pope St John Paul II visited Hiroshima in 1981, he made a powerful plea for peace. In response, the following year the Catholic Bishops of Japan instituted the Ten Days of Prayer for Peace initiative from 6-15th August each year for everyone to pray for, think about and act for Peace. Last year, in their message commemorating the 75th anniversaries of the bombings of Nagasaki and Hiroshima, the Catholic Bishops of Japan advocated for the protection of all life, the abandoning of war and permanent peace.

While most, if not all, of us are not directly involved in promoting armed conflict, there is one area where we might be complicit: our investments. For those who also want to take action to achieve peace, this is one thing we can do – examine our investments and divest of them if they are in weapons. Pope Francis has recognised that one of the causes of the third world war fought piecemeal is the constant production of ever more destructive weaponry.

Pope Francis has followed in the footsteps of his predecessor Pope St. John XXIII who among other means also sought peace by encouraging complete disarmament: “Unless this process of disarmament be thoroughgoing and complete, and reach men’s very souls, it is impossible to stop the arms race, or to reduce armaments, or – and this is the main thing – ultimately to abolish them entirely.’” (Pacem in Terris, 113). Pope Francis has also declared that it is no longer tolerable to manufacture and traffic in weaponry, especially when that money can be used to treat people and save lives.

So from the 6th-15th of August 2021, we invite you to pray and act for peace in our world.

Please see below the a prayer for nuclear disarmament and peace which was written by the Office for Social Justice.


A Prayer for Nuclear Disarmament

Lord of all creation, make us instruments of your peace.

Let us learn the lessons of the past, and put an end to nuclear weapons.

Where there is hatred, let us sow love.

May our love for each other and for all of your creation

leave no place for making or owning weapons of mass destruction.

Where there is injury, let us be bearers of your healing and pardon.

May we create paths to dialogue, understanding and reconciliation.

Where there is doubt, let us foster faith in you.

May we let the weapons fall from our hands and know that you are God.

Where there is despair, let us hold up hope.

May our lives reflect your love in the face of violence,

knowing that love is stronger than death.

Where there is darkness, let us be bearers of your light.

May our choices show that peace is possible.

Where there is sadness, let us bring the joy of the Gospel.




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d previously unimaginable power of the atom had been demonstrated. In the following years several governments joined the arms race, while internationally, efforts were focused on constraining the threat of nuclear weapons proliferation.

From the 1950s the power of the atom was harnessed increasingly for peaceful uses, notably electricity generation and medicine. Nowhere is the transition from weapons of destruction to power for good better displayed than Hiroshima and Nagasaki in Japan which have come to depend substantially on electricity from nuclear energy.

Today, as the main nuclear arsenals are being dismantled and a comprehensive test ban treaty is in sight, commercial nuclear power provides a significant portion of the world’s electricity. Several factors suggest that nuclear power has a much larger role to play in supplying the world’s future energy needs, and this is supported by every reputable projection.

The first two atomic bombs in 1945

The Hiroshima bomb was made from highly-enriched uranium-235. This was prepared by diffusion enrichment techniques using the very small differences in mass of the two main isotopes: U-235 (originally 0.7% in the uranium) and U-238, the majority. As UF6 , there is about a one percent difference in mass between the molecules, and this enables concentration of the less common isotope. About 64 kilograms of highly-enriched uranium was used in the bomb which had a 16 kiloton yield (i.e. it was equivalent to 16,000 tonnes of TNT). It was released over Hiroshima, Japan’s seventh largest city, on 6 August 1945. Some 90% of the city was destroyed.

The 21 kiloton explosive charge for the bomb detonated over Nagasaki three days later was provided by about 6.2 kilograms of plutonium-239 (>90% Pu-239), and its preparation depended on the operation of special nuclear reactors built for the purpose. During 1942, under conditions of wartime secrecy, the first human-designed reactor* had been constructed, in a squash court at the University of Chicago. It used highly purified graphite to slow the neutrons released in fission to enable further fission. This paved the way for more substantial production reactors at Hanford. The plutonium-239 generated in these could be separated by simple chemical methods, with no need for the complexities of isotope separation.

* Several natural nuclear reactors functioned about 2 billion years ago in Africa.

However, the design of a plutonium bomb is very much more complex than one using enriched uranium. Hence the need to test it, and in fact the plutonium was first used for a test explosion at Alamogordo in New Mexico on 16 July 1945, ushering in the nuclear age with all its threat and promise.

The effects of the Hiroshima and Nagasaki bombs

The devastating effects of both kinds of bombs depended essentially upon the energy released at the moment of the explosion, causing immediate fires, destructive blast pressures, and extreme local radiation exposures. Since the bombs were detonated at a height of some 600 metres above the ground, very little of the fission products were deposited on the ground beneath. Some deposition occurred however in areas near to each city, owing to local rainfall occurring soon after the explosions. This happened at positions a few kilometres to the east of Nagasaki, and in areas to the west and north-west of Hiroshima. For the most part, however, these fission products were carried high into the upper atmosphere by the heat generated in the explosion itself. The majority would have decayed by the time they landed around the globe.

In Hiroshima, of a resident civilian population of 250,000 it was estimated that 45,000 died on the first day and a further 19,000 during the subsequent four months. (Another figure is 78,500 fatalities, with 5 to 15% of the short-term ones being from radiation.) In Nagasaki, out of a population of 174,000, on the first day 22,000 died and another 17,000 within four months. Unrecorded deaths of military personnel and foreign workers may have added considerably to these figures. About 15 square kilometres (over 50%) of the two cities was destroyed.

It is uncertain what proportion of these 103,000 deaths, or of the further deaths in military personnel, were due to radiation exposure rather than to the very high temperatures and blast pressures caused by the explosions – 15 kilotons at Hiroshima and 25 kilotons at Nagasaki. From the estimated radiation levels, however, it is apparent that radiation alone would not have been enough cause death in most of those exposed beyond a kilometre of the ground zero below the bombs. Most deaths were from blast injuries or burns rather than the radiation. Beyond 1.5 km the radiation risk would have been much reduced (and 24 Australian prisoners of war about 1.5 km from the Nagasaki ground zero survived and many lived to a healthy old age).

In comparison, during the period of February 1945 to August 1945, the US bombing of Japanese cities – notably Tokyo, Nagoya, Osaka and Kobe – by B-29s delivered about 100 kilotons of high explosives and incendiaries to urban areas in hundreds of raids, resulting in a large number of deaths and causing widespread destruction. Some 80,000 to 100,000 people were killed in a single 300-bomber raid on Tokyo. About 80 square kilometers of those four cities was destroyed in ten days during March. Overall 67 Japanese cities were partly destroyed, 500,000 people were killed and 5 million more made homeless.

To the 103,000 deaths from the blast or acute radiation exposure at Hiroshima and Nagasaki have since been added those due to radiation induced cancers and leukaemia, which amounted to some 400 within 30 years, and which may ultimately reach about 550. (Some 93,000 exposed survivors were still being monitored 50 years later.) There was an increase in leukaemia beginning about two years later and peaking at four to six years later, and other cancers beginning about ten years later.  There was no evident to suggest an increase in leukaemia at less than 500 mSv acute dose. At an acute dose of 100 mSv, an increased cancer risk of 1.05 times normal was calculated. There was concern about ingestion or inhalation of radionuclides, but fires released far higher levels of non-radioactive carcinogens. Additionally, no genetic damage has been detected in survivors’ children, despite careful and continuing investigation by a joint Japanese-US foundation.

The major source of exposure in both cities was from the penetrating gamma radiations, and to a lesser extent from the neutrons (mostly at Hiroshima), emitted during and shortly after fission. There were two further, and smaller, sources of exposure. One, already mentioned, was due to the ‘black rain’ which fell in some areas, carrying down radioactive materials from within the rising cloud of fission products. The exposures due to these depositions are in general estimated to have been small, but some increased activity from the fission product radionuclide caesium-137 remained detectable for many years in soil and farm products in the Nishiyama district east of Nagasaki.

The second additional form of exposure resulted from the effect of neutrons in inducing radioactivity in various stable chemical elements such as in iron or concrete structures or roofing tiles. The total absorbed doses of radiation from these activation products are estimated to be less than one per cent of that from the neutrons which induced them. They could however have caused a significant exposure of people who entered the city within a few days of the explosions.


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