August 6, 1945 the explosion of an atomic bomb over the city ofHiroshima, at Japan, precipitates the end of World War II. Since then, fear has hovered over the world that a nuclear conflict could degenerate into the total destruction of humanity.

An old project

Atomic bomb over Hiroshima

Atomic bomb over Hiroshima

Even before World War II, Americans worried about the risk of the Nazis developing a bomb of exceptional lethal power thanks to the principle of nuclear fission.

Wishing to get ahead of them at all costs, President Roosevelt inaugurates a secret A-bomb development program in 1942. As the Americans finalize the bomb, Nazi Germany is preparing to surrender unconditionally.

Only Japan still poses a threat, but its military, industrial and scientific power is much lower than that of Germany.

Desperate resistance from Japan

Led by die-hard generals, Japan persists in a desperate resistance, which conventional bombardments do not weaken. The simple capture of the island ofOkinawa cost the US military 7,600 lives. The American staff fears losing 500,000 soldiers to conquer Honshu, the main island of the archipelago.

This is how the idea ofuse the atomic bomb against the Empire of the Rising Sun, to break its resistance cheaply. President Roosevelt died on April 12, 1945 and his successor, Harry truman, takes over this project.

It offers the Americans the advantage of annihilating Japan without the help of Stalin, who has not yet declared war on it, and of displaying all their military might before the Soviet dictator.

On July 16, 1945, the Americans carried out a first nuclear test in the New Mexico desert. The experiment is fully successful, but due to lack of experience, scientists do not precisely measure the effects of the atomic bomb on populations.

On July 26, the United States, Britain and China issue an ultimatum to Japan that implicitly alludes to a terrifying weapon.

Hiroshima after the bomb

Hiroshima after the bomb

The bombardment

Hiroshima city chosen as target because it has not yet suffered air raids: it constitutes an ideal zone to evaluate the impact of the bomb. The center of the city has several reinforced concrete buildings, as well as less solid constructions.

On the outskirts, wooden houses sit alongside small shops, forming a dense collection of lightweight structures. A few factories are located in the suburbs.

Fire risk is high in Hiroshima: the concentration of buildings and the materials used were conducive to maximum destruction thanks to the thermal effects of the bomb.

Information on the number of people present in the city during the bombing varies widely, ranging from 255,000 to 348,000 inhabitants. Estimates given by troops and workers are probably imprecise.

The American report indicating 255,000 inhabitants based on rice rationing statistics from June 1945. Hiroshima is the priority target for the bombing.

On August 6, 1945, the weather was clear over the city. Several B-29s (including Jabbit III for Kokura and Full House for Nagasaki) had been sent to the other targets if the mission to Hiroshima were to be hijacked, but the other towns were all covered in clouds.

The B-29 piloted by Paul Tibbets left at 2:45 am from Tinian Island. The plane carries the bomb with it Little boy. It is armed in flight by Navy Captain William Parsons after take off.

About an hour before the bombardment, the Japanese detected the approach of an American plane on the south of the archipelago. The alert was triggered with announcements for the population and a shutdown of radio programs in several towns. The plane flies over Hiroshima and disappears.

This aircraft is in fact the reconnaissance B-29, Straight Flush, which signals good visibility conditions for the bombardment.

Japanese radars then detected a new group of planes at high altitude, but their small number, only three, caused the alert to be lifted after ten minutes. The recommendations for the population were to reach the shelters if a B-29 was visible, but no raids were expected other than reconnaissance.

Hiroshima survivors

Hiroshima survivors

It is in fact the three B-29 of the raid on Hiroshima which evolve at more than 9,500 meters of altitude:

  • Enola Gay (bombing raid)
  • The Great Artist (measurements and data collection)
  • Necessary Evil (photographs, films)

The second lieutenant, Morris R. Jeppson, was the last to touch the bomb when placing the weapon fuses. Shortly before 8:15 am, Enola Gay arrives above the city. The order to bomb is given by Tibbets, Major Thomas Ferebee does so by aiming at the Aioi “T” -shaped bridge, which constitutes an ideal landmark in the center of the city.

Shortly after 8:15 am, the bomb Little boy comes out of the cargo hold at an altitude of 9,450 m. At 8:16 m2, after about 43 seconds of free fall, activated by the altitude sensors and its radars, it exploded 580 meters above the Shima hospital, in the heart of Hiroshima, 170 m southeast of the target bridge, releasing an energy equivalent to approximately 15,000 tonnes of TNT.

A huge bubble of glowing gas over 400 meters in diameter forms in fractions of a second, emitting a powerful heat radiation. Below, near the hypocenter, the temperature of the surfaces exposed to this radiation rises for a brief moment, very superficially, to perhaps 4.000 ° C.

Fires break out, even several kilometers away. People exposed to this flash are burned. Those protected inside or by the shadow of buildings are buried or injured by projections of debris when, a few seconds later, the shock wave is coming on them.

Winds of 300 to 800 km / h devastate streets and homes. The long ordeal of the survivors has only just begun, as the atomic mushroom, sucking up dust and debris, begins its ascent of several kilometers.

A huge, generalized fire breaks out quickly with temperature spikes in some places.

If some areas are spared during the explosion, they will subsequently have to face a deluge of fire caused by the intense movements of air masses. This “firestorm” is similar to those observed during the incendiary bombardments on German cities.

Atomic bomb victim

Atomic bomb victim

Enola Gay has meanwhile made a sharp 155 ° turn to the northwest and turned back. Members of the crew, protected by glasses, can witness the explosion.

Bob Lewis, Enola Gay’s co-pilot, exclaims: “ My God, what have we done? Even though I live a hundred years, I’ll forever keep those few minutes in mind “.

The bomber returns to Tinian where the crew is decorated for their mission and where a big party awaits them.

The other two B-29s tasked with collecting data remained around the site of the explosion long enough to photograph the atomic mushroom and the damage, film the surroundings and gather information on the mission.

The dropping of an atomic bomb by an American B-29 plane on the Japanese city of Hiroshima on August 6, 1945, then another on Nagasaki, three days later, contributed, along with other factors, to the surrender. of Japan and at the end of World War II.

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